Internet Engineering Task Force (IETF)                        R. Danyliw
Request for Comments: 7970                                          CERT
Obsoletes: 5070, 6685                                      November 2016
Category: Standards Track
ISSN: 2070-1721

The Incident Object Description Exchange Format Version 2

Abstract

   The Incident Object Description Exchange Format (IODEF) defines a
   data representation for security incident reports and indicators
   commonly exchanged by operational security teams for mitigation and
   watch and warning.  This document describes an updated information
   model for the IODEF and provides an associated data model specified
   with the XML schema.  This new information and data model obsoletes
   RFCs 5070 and 6685.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7970.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Contributions published or made publicly available before November
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   Without obtaining an adequate license from the person(s) controlling
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   it for publication as an RFC or to translate it into languages other
   than English.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.2.  Notations . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  About the IODEF Data Model  . . . . . . . . . . . . . . .   7
     1.4.  Changes from RFC 5070 . . . . . . . . . . . . . . . . . .   7
   2.  IODEF Data Types  . . . . . . . . . . . . . . . . . . . . . .   9
     2.1.  Integers  . . . . . . . . . . . . . . . . . . . . . . . .   9
     2.2.  Real Numbers  . . . . . . . . . . . . . . . . . . . . . .   9
     2.3.  Characters and Strings  . . . . . . . . . . . . . . . . .   9
     2.4.  Multilingual Strings  . . . . . . . . . . . . . . . . . .   9
     2.5.  Binary Strings  . . . . . . . . . . . . . . . . . . . . .  10
       2.5.1.  Base64 Bytes  . . . . . . . . . . . . . . . . . . . .  10
       2.5.2.  Hexadecimal Bytes . . . . . . . . . . . . . . . . . .  11
     2.6.  Enumerated Types  . . . . . . . . . . . . . . . . . . . .  11
     2.7.  Date-Time String  . . . . . . . . . . . . . . . . . . . .  11
     2.8.  Timezone String . . . . . . . . . . . . . . . . . . . . .  11
     2.9.  Port Lists  . . . . . . . . . . . . . . . . . . . . . . .  11
     2.10. Postal Address  . . . . . . . . . . . . . . . . . . . . .  12
     2.11. Telephone Number  . . . . . . . . . . . . . . . . . . . .  12
     2.12. Email String  . . . . . . . . . . . . . . . . . . . . . .  12
     2.13. Uniform Resource Locator Strings  . . . . . . . . . . . .  12
     2.14. Identifiers and Identifier References . . . . . . . . . .  12
     2.15. Software  . . . . . . . . . . . . . . . . . . . . . . . .  13
       2.15.1.  SoftwareReference Class  . . . . . . . . . . . . . .  14
     2.16. Extension . . . . . . . . . . . . . . . . . . . . . . . .  15
   3.  The IODEF Information Model . . . . . . . . . . . . . . . . .  18
     3.1.  IODEF-Document Class  . . . . . . . . . . . . . . . . . .  18
     3.2.  Incident Class  . . . . . . . . . . . . . . . . . . . . .  20
     3.3.  Common Attributes . . . . . . . . . . . . . . . . . . . .  23
       3.3.1.  restriction Attribute . . . . . . . . . . . . . . . .  23
       3.3.2.  observable-id Attribute . . . . . . . . . . . . . . .  25
     3.4.  IncidentID Class  . . . . . . . . . . . . . . . . . . . .  25
     3.5.  AlternativeID Class . . . . . . . . . . . . . . . . . . .  26
     3.6.  RelatedActivity Class . . . . . . . . . . . . . . . . . .  27
     3.7.  ThreatActor Class . . . . . . . . . . . . . . . . . . . .  28
     3.8.  Campaign Class  . . . . . . . . . . . . . . . . . . . . .  29
     3.9.  Contact Class . . . . . . . . . . . . . . . . . . . . . .  30
       3.9.1.  RegistryHandle Class  . . . . . . . . . . . . . . . .  34
       3.9.2.  PostalAddress Class . . . . . . . . . . . . . . . . .  35
       3.9.3.  Email Class . . . . . . . . . . . . . . . . . . . . .  36
       3.9.4.  Telephone Class . . . . . . . . . . . . . . . . . . .  37
     3.10. Discovery Class . . . . . . . . . . . . . . . . . . . . .  38
       3.10.1.  DetectionPattern Class . . . . . . . . . . . . . . .  40
     3.11. Method Class  . . . . . . . . . . . . . . . . . . . . . .  41
       3.11.1.  Reference Class  . . . . . . . . . . . . . . . . . .  42

     3.12. Assessment Class  . . . . . . . . . . . . . . . . . . . .  43
       3.12.1.  SystemImpact Class . . . . . . . . . . . . . . . . .  45
       3.12.2.  BusinessImpact Class . . . . . . . . . . . . . . . .  48
       3.12.3.  TimeImpact Class . . . . . . . . . . . . . . . . . .  50
       3.12.4.  MonetaryImpact Class . . . . . . . . . . . . . . . .  52
       3.12.5.  Confidence Class . . . . . . . . . . . . . . . . . .  53
     3.13. History Class . . . . . . . . . . . . . . . . . . . . . .  54
       3.13.1.  HistoryItem Class  . . . . . . . . . . . . . . . . .  54
     3.14. EventData Class . . . . . . . . . . . . . . . . . . . . .  57
       3.14.1.  Relating the Incident and EventData Classes  . . . .  59
       3.14.2.  Recursive Definition of EventData  . . . . . . . . .  59
     3.15. Expectation Class . . . . . . . . . . . . . . . . . . . .  60
     3.16. Flow Class  . . . . . . . . . . . . . . . . . . . . . . .  63
     3.17. System Class  . . . . . . . . . . . . . . . . . . . . . .  64
     3.18. Node Class  . . . . . . . . . . . . . . . . . . . . . . .  67
       3.18.1.  Address Class  . . . . . . . . . . . . . . . . . . .  68
       3.18.2.  NodeRole Class . . . . . . . . . . . . . . . . . . .  69
       3.18.3.  Counter Class  . . . . . . . . . . . . . . . . . . .  73
     3.19. DomainData Class  . . . . . . . . . . . . . . . . . . . .  75
       3.19.1.  Nameservers Class  . . . . . . . . . . . . . . . . .  77
       3.19.2.  DomainContacts Class . . . . . . . . . . . . . . . .  78
     3.20. Service Class . . . . . . . . . . . . . . . . . . . . . .  79
       3.20.1.  ServiceName Class  . . . . . . . . . . . . . . . . .  80
       3.20.2.  ApplicationHeader Class  . . . . . . . . . . . . . .  81
     3.21. EmailData Class . . . . . . . . . . . . . . . . . . . . .  82
     3.22. Record Class  . . . . . . . . . . . . . . . . . . . . . .  83
       3.22.1.  RecordData Class . . . . . . . . . . . . . . . . . .  84
       3.22.2.  RecordPattern Class  . . . . . . . . . . . . . . . .  85
     3.23. WindowsRegistryKeysModified Class . . . . . . . . . . . .  87
       3.23.1.  Key Class  . . . . . . . . . . . . . . . . . . . . .  88
     3.24. CertificateData Class . . . . . . . . . . . . . . . . . .  89
       3.24.1.  Certificate Class  . . . . . . . . . . . . . . . . .  90
     3.25. FileData Class  . . . . . . . . . . . . . . . . . . . . .  90
       3.25.1.  File Class . . . . . . . . . . . . . . . . . . . . .  91
     3.26. HashData Class  . . . . . . . . . . . . . . . . . . . . .  92
       3.26.1.  Hash Class . . . . . . . . . . . . . . . . . . . . .  94
       3.26.2.  FuzzyHash Class  . . . . . . . . . . . . . . . . . .  95
     3.27. SignatureData Class . . . . . . . . . . . . . . . . . . .  95
     3.28. IndicatorData Class . . . . . . . . . . . . . . . . . . .  96
     3.29. Indicator Class . . . . . . . . . . . . . . . . . . . . .  96
       3.29.1.  IndicatorID Class  . . . . . . . . . . . . . . . . .  99
       3.29.2.  AlternativeIndicatorID Class . . . . . . . . . . . . 100
       3.29.3.  Observable Class . . . . . . . . . . . . . . . . . . 101
       3.29.4.  IndicatorExpression Class  . . . . . . . . . . . . . 106
       3.29.5.  Expressions with IndicatorExpression . . . . . . . . 108
       3.29.6.  ObservableReference Class  . . . . . . . . . . . . . 110
       3.29.7.  IndicatorReference Class . . . . . . . . . . . . . . 110
       3.29.8.  AttackPhase Class  . . . . . . . . . . . . . . . . . 111

   4.  Processing Considerations . . . . . . . . . . . . . . . . . . 112
     4.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . 112
     4.2.  IODEF Namespace . . . . . . . . . . . . . . . . . . . . . 112
     4.3.  Validation  . . . . . . . . . . . . . . . . . . . . . . . 112
     4.4.  Incompatibilities with v1 . . . . . . . . . . . . . . . . 113
   5.  Extending the IODEF . . . . . . . . . . . . . . . . . . . . . 114
     5.1.  Extending the Enumerated Values of Attributes . . . . . . 114
       5.1.1.  Private Extension of Enumerated Values  . . . . . . . 114
       5.1.2.  Public Extension of Enumerated Values . . . . . . . . 115
     5.2.  Extending Classes . . . . . . . . . . . . . . . . . . . . 115
     5.3.  Deconflicting Private Extensions  . . . . . . . . . . . . 117
   6.  Internationalization Issues . . . . . . . . . . . . . . . . . 118
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . 119
     7.1.  Minimal Example . . . . . . . . . . . . . . . . . . . . . 119
     7.2.  Indicators from a Campaign  . . . . . . . . . . . . . . . 120
   8.  The IODEF Data Model (XML Schema) . . . . . . . . . . . . . . 121
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . 161
     9.1.  Security  . . . . . . . . . . . . . . . . . . . . . . . . 161
     9.2.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 162
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 163
     10.1.  Namespace and Schema . . . . . . . . . . . . . . . . . . 163
     10.2.  Enumerated Value Registries  . . . . . . . . . . . . . . 163
     10.3.  Expert Review of IODEF-Related XML Registry Entries  . . 166
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . 167
     11.1.  Normative References . . . . . . . . . . . . . . . . . . 167
     11.2.  Informative References . . . . . . . . . . . . . . . . . 170
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 171
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 172

1. Introduction

   Organizations require help from other parties to mitigate malicious
   activity targeting their network and to gain insight into potential
   threats.  This coordination might entail working with an ISP to
   filter attack traffic, contacting a remote site to take down a
   botnet, or sharing watch lists of known malicious indicators in a
   consortium.

   The Incident Object Description Exchange Format (IODEF) is a format
   for representing computer security information commonly exchanged
   between Computer Security Incident Response Teams (CSIRTs) or other
   operational security teams.  It provides an XML representation for
   conveying:

   o  indicators to characterize a threat;

   o  security incident reports to document attacks against an
      organization;

   o  response activity taken or that could be taken in response to an
      incident; and

   o  metadata so that these various classes of information can be
      exchanged among parties.

   The purpose of the IODEF is to enhance the operational capabilities
   of CSIRTs.  Adoption of the IODEF will improve the ability of a CSIRT
   to resolve security incidents; understand threats; and coordinate
   response activities and proactive mitigations by simplifying
   collaboration and data sharing with its partners.  This structured
   format provided by the IODEF allows for:

   o  machine-to-machine exchange of incident and indicator data;

   o  automated processing of this data whereby allowing more rapid
      execution of appropriate courses of action; and

   o  the development of an ecosystem of interoperable tools enabling
      security operations.

   Sharing and coordinating with other organizations is not strictly a
   technical problem.  There are numerous procedural, cultural, legal,
   and trust-related barriers to overcome.  The IODEF does not attempt
   to address them directly.  However, operational implementations of
   the IODEF will need to consider these challenges.

   Section 1 provides the background for the IODEF.  Sections 3 and 8
   specify the IODEF information and data model, respectively.  The data
   types used in this document are described in Section 2.  Processing
   considerations, extending the specification, internationalization,
   and security issues are covered in Sections 4, 5, 6, and 9,
   respectively.  Examples are listed in Section 7.

1.1. Terminology

   The key words "MUST," "MUST NOT," "REQUIRED," "SHALL," "SHALL NOT,"
   "SHOULD," "SHOULD NOT," "RECOMMENDED," "MAY," and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2. Notations

   The IODEF is specified as an Extensible Markup Language (XML)
   [W3C.XML] schema [W3C.SCHEMA].  The normative IODEF data model is
   found in the XML schema in Section 8.  To aid in the understanding of
   the data elements, Section 3 also depicts the underlying information
   model using Unified Modeling Language (UML).  This abstract
   presentation of the IODEF is not normative.

   For clarity in this document, the term "XML document" will be used
   when referring generically to any instance of an XML document.  The
   term "IODEF document" will be used to refer to an XML document
   conforming to the IODEF specification.  The terms "schema" will be
   used to refer to Section 8 of this document.  The terms "data model"
   and "schema" will be used interchangeably.  The terms "class" and
   "element" will be used to reference either the corresponding data
   element in the UML-based information or XML schema-based data models,
   respectively.

1.3. About the IODEF Data Model

   A number of considerations were made in the design of the IODEF data
   model.

   o  The data model found in this document is an evolution of the one
      previously specified in [RFC5070].  New fields were added to
      represent additional information.  [RFC5070] was developed
      primarily to represent incident reports.  This document builds
      upon it by adding support for indicators and revising it to
      reflect the current challenges faced by CSIRTs.  An attempt was
      made to preserve backward compatibility, but this was not possible
      in all cases.  See Section 4.4.  This document obsoletes
      [RFC5070].

   o  The IODEF is a transport format.  Therefore, the data model may
      not be the optimal archival or in-memory processing format.

   o  The IODEF is intended to be a framework to convey only commonly
      exchanged information.  It ensures that there are mechanisms for
      extensibility to support organization-specific information and
      techniques to reference information kept outside of the data
      model.

   o  Not all commonly exchanged information has a well-defined format
      or taxonomy.  The IODEF attempts to strike a balance between
      enforcing sufficient structure to allow automated processing and
      supporting free-form content that enables maximum flexibility.

   o  The IODEF fits into a broader ecosystem of standards and
      conventions.  An attempt was made to harmonize the data model with
      this context.

1.4. Changes from RFC 5070

   A detailed list of additions made to the data model in [RFC5070] are
   enumerated in this section.  See Section 4.4 for a list of
   incompatible changes.

   o  Updated the data types (Section 2) to improve
      internationalization, clarify ambiguity, and ensure consistency in
      extensions.

   o  Added the observable-id attribute (Section 3.3.2) and
      IndicatorData class (Section 3.28) to represent indicators.

   o  Added the private-enum-name and private-enum-id attributes to the
      IODEF-Document class (Section 3.1) to disambiguate private
      extensions.

   o  Updated the Incident class (Section 3.2) to represent additional
      timing and workflow information.

   o  Added the ThreatActor (Section 3.7) and Campaign (Section 3.8)
      classes to represent attack attribution information.

   o  Updated the Contact class (Section 3.9) and its children to
      improve internationalization and represent additional information
      about an entity.

   o  Updated the Method class (Section 3.11) to improve extensibility
      through externally referenced resources.

   o  Added the Discovery class (Section 3.10) to describe how an
      incident was discovered.

   o  Updated the Assessment class (Section 3.12) to enable more
      descriptive characterizations of the impact of an incident.

   o  Updated the HistoryItem (Section 3.13.1) and Expectation
      (Section 3.15) classes to support a reference to a course of
      action.

   o  Updated the EventData class (Section 3.14) with additional
      metadata added to the Incident class.

   o  Updated the System class (Section 3.17) with additional metadata.

   o  Updated the Counter class (Section 3.18.3) to support additional
      rate metrics.

   o  Added DomainData (Section 3.19), EmailData (Section 3.21),
      WindowsRegistryKeysModified (Section 3.23), CertificateData
      (Section 3.24), and FileData (Section 3.25) classes to improve the
      description of an incident and support this data as indicators.

   o  Added the SignatureData (Section 3.27) and HashData (Section 3.26)
      classes to represent digital signatures and hashes.

   o  Added support for public enumerated attribute extensions using
      IANA registries (Section 5.1.2).

   o  Updated numerous enumerated attributes for completeness.

2. IODEF Data Types

The IODEF uses a number of simple and complex types. This section
describes these data types.

2.1. Integers

   An integer is represented in the information model by the INTEGER
   data type.  Integer data MUST be encoded in Base 10.

   The INTEGER data type is implemented in the data model as an
   "xs:integer" type per Section 3.3.13 of [W3C.SCHEMA.DTYPES].

2.2. Real Numbers

   A real (floating-point) number is represented in the information
   model by the REAL data type.  Real data MUST be encoded in Base 10.

   The REAL data type is implemented in the data model as an "xs:float"
   type per Section 3.2.4 of [W3C.SCHEMA.DTYPES].

2.3. Characters and Strings

   A single character is represented in the information model by the
   CHARACTER data type.  A string is represented by the STRING data
   type.  Special characters MUST be encoded using entity references.
   See Section 4.1.

   The CHARACTER and STRING data types are implemented in the data model
   as an "xs:string" type per Section 3.2.1 of [W3C.SCHEMA.DTYPES].

2.4. Multilingual Strings

   A string that needs to be represented in a human-readable language
   different than the default encoding of the document is represented in
   the information model by the ML_STRING data type.

   The ML_STRING data type is implemented in the data model as the
   "iodef:MLStringType" type.  This type extends the "xs:string" to
   include two attributes.

   +------------------------+
   | iodef:MLStringType     |
   +------------------------+
   | xs:string              |
   |                        |
   | ENUM xml:lang          |
   | STRING translation-id  |
   +------------------------+

                   Figure 1: The iodef:MLStringType Type

   The content of the class is a character string of type "xs:string"
   whose language MAY be specified by the xml:lang attribute.

   The attributes of the iodef:MLStringType type are:

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and format are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   translation-id
      Optional.  STRING.  An identifier to relate other instances of
      this class with the same parent as translations of this text.  The
      scope of this identifier is limited to all of the direct, peer
      child classes of a given parent class.

   Using this class enables representing translations of the same text
   in multiple languages.  Each translation is a distinct instance of
   this class with a common parent.  A group of classes each with a
   translated instance of text is related by setting a common identifier
   in the translation-id attribute.  The language of a given class is
   set by the xml:lang attribute.  See Section 6 for more details on
   representing translations of free-form text.

2.5. Binary Strings

Binary octets can be represented with two encodings.

2.5.1. Base64 Bytes

   A binary octet encoded with base64 is represented in the information
   model by the BYTE data type.  A sequence of these octets is of the
   BYTE[] data type.

   The BYTE and BYTE[] data types are implemented in the data model as
   an "xs:base64Binary" type per Section 3.2.16 of [W3C.SCHEMA.DTYPES].

2.5.2. Hexadecimal Bytes

   A binary octet encoded as a character tuple consistent of two
   hexadecimal digits is represented in the information model by the
   HEXBIN data type.  A sequence of these octets is of the HEXBIN[] data
   type.

   The HEXBIN and HEXBIN[] data types are implemented in the data model
   as an "xs:hexBinary" type per Section 3.2.15 of [W3C.SCHEMA.DTYPES].

2.6. Enumerated Types

   An enumerated type is represented in the information model by the
   ENUM data type.  It is an ordered list of acceptable string values.
   Each value has a representative keyword.  Within the data model, the
   enumerated type keywords are used as attribute values.

   The ENUM data type is implemented in the data model as values of an
   "xs:NMTOKEN" type per Section 3.3.4 of [W3C.SCHEMA.DTYPES].

2.7. Date-Time String

   A date-time string that describes a particular instant in time is
   represented in the information model by the DATETIME data type.
   Ranges are not supported.

   The DATETIME data type is implemented in the data model as an
   "xs:dateTime" type per Section 3.2.7 of [W3C.SCHEMA.DTYPES].

2.8. Timezone String

   A timezone offset from UTC is represented in the information model by
   the TIMEZONE data type.  It is formatted according to the following
   regular expression: "Z|[\+\-](0[0-9]|1[0-4]):[0-5][0-9]".

   The TIMEZONE data type is implemented in the data model as an
   "iodef:TimezoneType" type.

2.9. Port Lists

   A list of network ports is represented in the information model by
   the PORTLIST data type.  A PORTLIST consists of a comma-separated
   list of numbers and ranges (N-M means ports N through M, inclusive).
   It is formatted according to the following regular expression:
   "\d+(\-\d+)?(,\d+(\-\d+)?)*".  For example,
   "2,5-15,30,32,40-50,55-60".

The PORTLIST data type is implemented in the data model as an
"iodef:PortlistType" type.

2.10. Postal Address

   A postal address is represented in the information model by the
   POSTAL data type.  The format of the POSTAL data type is documented
   in Section 2.23 of [RFC4519] as a free-form multi-line string
   separated by the "$" character.

   The POSTAL data type is implemented in the data model as an
   "iodef:MLStringType" type.

2.11. Telephone Number

   A telephone number is represented in the information model by the
   PHONE data type.  The format of the PHONE data type is documented in
   [E.164].

   The PHONE data type is implemented in the data model as an
   "xs:string" type per Section 3.2.1 of [W3C.SCHEMA.DTYPES].

2.12. Email String

   An email address is represented in the information model by the EMAIL
   data type.  The format of the EMAIL data type is documented in
   Section 3.4.1 of [RFC5322] and Section 3.3 of [RFC6531].

   The EMAIL data type is implemented in the data model as an
   "xs:string" type per Section 3.2.1 of [W3C.SCHEMA.DTYPES].

2.13. Uniform Resource Locator Strings

   A uniform resource locator (URL) is represented in the information
   model by the URL data type.  The format of the URL data type is
   documented in [RFC3986].

   The URL data type is implemented as an "xs:anyURI" type per
   Section 3.2.17 of [W3C.SCHEMA.DTYPES].

2.14. Identifiers and Identifier References

   An identifier unique to the IODEF document is represented in the
   information model by the ID data type.  A reference to this
   identifier is represented by the IDREF data type.

   The ID and IDREF data types are implemented in the model as "xs:ID"
   and "xs:IDREF" types per Sections 3.3.8 and 3.3.9 of
   [W3C.SCHEMA.DTYPES].

2.15. Software

   A particular version of software is represented in the information
   model by the SOFTWARE data type.  This software can be described by
   using a reference, a URL, or with free-form text.

   The SOFTWARE data type is implemented in the data model as the
   "iodef:SoftwareType" type.

   +--------------------+
   | iodef:SoftwareType |
   +--------------------+
   |                    |<>--{0..1}--[ SoftwareReference ]
   |                    |<>--{0..*}--[ URL               ]
   |                    |<>--{0..*}--[ Description       ]
   +--------------------+

                      Figure 2: The SoftwareType Type

   The aggregate classes of the SoftwareType type are:

   SoftwareReference
      Zero or one.  Reference to a software application.  See
      Section 2.15.1.

   URL
      Zero or more.  URL.  A URL to a resource describing the software.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      software.

   At least one of these classes MUST be present.

   The iodef:SoftwareType type has no attributes.

2.15.1. SoftwareReference Class

   The SoftwareReference class is a reference to a particular version of
   software.

   +----------------------+
   | SoftwareReference    |
   +----------------------+
   | xs:any               |
   |                      |
   | ENUM spec-name       |
   | STRING ext-spec-name |
   | ENUM dtype           |
   | STRING ext-dtype     |
   +----------------------+

                   Figure 3: The SoftwareReference Class

   The element content varies according to the value of the spec-name
   attribute.  It is defined in the data model as "xs:any" per
   [W3C.SCHEMA].

   The attributes of the SoftwareReference class are:

   spec-name
      Required.  ENUM.  Identifies the format and semantics of the
      element body of this class.  Formal standards and specifications
      can be referenced as well as a free-form text description with a
      user-provided data type.  These values are maintained in the
      "SoftwareReference-spec-id" IANA registry per Section 10.2

      1.  custom.  The element content is free-form and of the data type
          specified by the dtype attribute.  If this value is selected,
          then the dtype attribute MUST be set.

      2.  cpe.  The element content describes a Common Platform
          Enumeration (CPE) entry per [NIST.CPE].

3. swid. The element content describes a software identification
(SWID) tag per [ISO19770].

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-spec-name
      Optional.  STRING.  A means by which to extend the spec-name
      attribute.  See Section 5.1.1.

   dtype
      Optional.  ENUM.  The data type of the element content.  The
      permitted values for this attribute are shown below.  The default
      value is "string".  These values are maintained in the
      "SoftwareReference-dtype" IANA registry per Section 10.2.

      1.  bytes.  The element content is of type HEXBIN.

      2.  integer.  The element content is of type INTEGER.

      3.  real.  The element content is of type REAL.

4. string. The element content is of type STRING.

5. xml. The element content is XML. See Section 5.2.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-dtype
      Optional.  STRING.  A means by which to extend the dtype
      attribute.  See Section 5.1.1.

2.16. Extension

   Information not otherwise represented in the IODEF can be added using
   the EXTENSION data type.  This data type is a generic extension
   mechanism.

   The EXTENSION data type is implemented in the data model as the
   "iodef:ExtensionType" type.

   The data type of an EXTENSION is described by the dtype attribute.
   For simple information, atomic data types (e.g., integers, strings)
   are supported.  Their semantics are further described by the meaning
   and formatid attributes.  Encapsulating XML documents conforming to
   another schema is also supported.  A detailed discussion of extending
   the schema can be found in Section 5.  Additional coordination may be
   required to ensure that a recipient of a document using this type can
   parse and process it.

   +------------------------+
   | iodef:ExtensionType    |
   +------------------------+
   | xs:any                 |
   |                        |
   | STRING name            |
   | ENUM dtype             |
   | STRING ext-dtype       |
   | STRING meaning         |
   | STRING formatid        |
   | ENUM restriction       |
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                  Figure 4: The iodef:ExtensionType Type

   The element content of this type is the extension being added to the
   data model.  This content is defined in the data model as "xs:any"
   per [W3C.SCHEMA].

   The attributes of the iodef:ExtensionType type are:

   name
      Optional.  STRING.  A free-form name of the field or data element.

   dtype
      Required.  ENUM.  The data type of the element content.  The
      default value is "string".  These values are maintained in the
      "ExtensionType-dtype" IANA registry per Section 10.2.

      1.   boolean.  The element content is of type BOOLEAN.

      2.   byte.  The element content is of type BYTE.

      3.   bytes.  The element content is of type HEXBIN.

      4.   character.  The element content is of type CHARACTER.

      5.   date-time.  The element content is of type DATETIME.

6. ntpstamp. Same as date-time.

7. integer. The element content is of type INTEGER.

8. portlist. The element content is of type PORTLIST.

9. real. The element content is of type REAL.

10. string. The element content is of type STRING.

11. file. The element content is a base64-encoded binary file
encoded as a BYTE[] type.

12. path. The element content is a file-system path encoded as a
STRING type.

13. frame. The element content is a Layer 2 frame encoded as a
HEXBIN type.

14. packet. The element content is a Layer 3 packet encoded as a
HEXBIN type.

15. ipv4-packet. The element content is an IPv4 packet encoded
as a HEXBIN type.

16. ipv6-packet. The element content is an IPv6 packet encoded
as a HEXBIN type.

17. url. The element content is of type URL.

18. csv. The element content is a comma-separated value (CSV)
list per Section 2 of [RFC4180] encoded as a STRING type.

19. winreg. The element content is a Microsoft Windows registry
key encoded as a STRING type.

20. xml. The element content is XML. See Section 5.2.

      21.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-dtype
      Optional.  STRING.  A means by which to extend the dtype
      attribute.  See Section 5.1.1.

   meaning
      Optional.  STRING.  A free-form text description of the element
      content.

   formatid
      Optional.  STRING.  An identifier referencing the format or
      semantics of the element content.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.  The IODEF Information Model

   The specifics of the IODEF information model are discussed in this
   section.  Each class and its relationships with the other classes is
   described.  When necessary, clarifications are made about translating
   this information model to the schema in Section 8.

3.1. IODEF-Document Class

   The IODEF-Document class is the top level class in the IODEF data
   model.  All IODEF documents are an instance of this class.

   +--------------------------+
   | IODEF-Document           |
   +--------------------------+
   | STRING version           |<>--{1..*}--[ Incident       ]
   | ENUM xml:lang            |<>--{0..*}--[ AdditionalData ]
   | STRING format-id         |
   | STRING private-enum-name |
   | STRING private-enum-id   |
   +--------------------------+

                    Figure 5: The IODEF-Document Class

   The aggregate classes of the IODEF-Document class are:

   Incident
      One or more.  The information related to a single incident.  See
      Section 3.2.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the IODEF-Document class are:

   version
      Required.  STRING.  The IODEF specification version number to
      which this IODEF document conforms.  The value of this attribute
      MUST be "2.00".

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   format-id
      Optional.  STRING.  A free-form string to convey processing
      instructions to the recipient of the document.  Its semantics must
      be negotiated out of band.

   private-enum-name
      Optional.  STRING.  A globally unique identifier for the CSIRT
      generating the document to deconflict private extensions used in
      the document.  The fully qualified domain name (FQDN) associated
      with the CSIRT MUST be used as the identifier.  See Section 5.3.

   private-enum-id
      Optional.  STRING.  An organizationally unique identifier for an
      extension used in the document.  If this attribute is set, the
      private-enum-name MUST also be set.  See Section 5.3.

3.2. Incident Class

   The Incident class describes commonly exchanged information when
   reporting or sharing derived analysis from security incidents.

   +-------------------------+
   | Incident                |
   +-------------------------+
   | ENUM purpose            |<>----------[ IncidentID      ]
   | STRING ext-purpose      |<>--{0..1}--[ AlternativeID   ]
   | ENUM status             |<>--{0..*}--[ RelatedActivity ]
   | STRING ext-status       |<>--{0..1}--[ DetectTime      ]
   | ENUM xml:lang           |<>--{0..1}--[ StartTime       ]
   | ENUM restriction        |<>--{0..1}--[ EndTime         ]
   | STRING ext-restriction  |<>--{0..1}--{ RecoveryTime    ]
   | ID observable-id        |<>--{0..1}--[ ReportTime      ]
   |                         |<>----------[ GenerationTime  ]
   |                         |<>--{0..*}--[ Description     ]
   |                         |<>--{0..*}  [ Discovery       ]
   |                         |<>--{0..*}--[ Assessment      ]
   |                         |<>--{0..*}--[ Method          ]
   |                         |<>--{1..*}--[ Contact         ]
   |                         |<>--{0..*}--[ EventData       ]
   |                         |<>--{0..1}--[ IndicatorData   ]
   |                         |<>--{0..1}--[ History         ]
   |                         |<>--{0..*}--[ AdditionalData  ]
   +-------------------------+

                       Figure 6: The Incident Class

   The aggregate classes of the Incident class are:

   IncidentID
      One.  An incident tracking number assigned to this incident by the
      CSIRT that generated the IODEF document.  See Section 3.4.

   AlternativeID
      Zero or one.  The incident tracking numbers used by other CSIRTs
      to refer to the incident described in the document.  See
      Section 3.5.

   RelatedActivity
      Zero or more.  Related activity and attribution of this activity.
      See Section 3.6.

   DetectTime
      Zero or one.  DATETIME.  The time the incident was first detected.

   StartTime
      Zero or one.  DATETIME.  The time the incident started.

   EndTime
      Zero or one.  DATETIME.  The time the incident ended.

   RecoveryTime
      Zero or one.  DATETIME.  The time the site recovered from the
      incident.

   ReportTime
      Zero or one.  DATETIME.  The time the incident was reported.

   GenerationTime
      One.  DATETIME.  The time the content in this Incident class was
      generated.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      incident.

   Discovery
      Zero or more.  The means by which this incident was detected.  See
      Section 3.10.

   Assessment
      Zero or more.  A characterization of the impact of the incident.
      See Section 3.12.

   Method
      Zero or more.  The techniques used by the threat actor in the
      incident.  See Section 3.11.

   Contact
      One or more.  Contact information for the parties involved in the
      incident.  See Section 3.9.

   EventData
      Zero or more.  Description of the events comprising the incident.
      See Section 3.14.

   IndicatorData
      Zero or one.  Indicators from the analysis of an incident.  See
      Section 3.28.

   History
      Zero or one.  A log of significant events or actions that occurred
      during the course of handling the incident.  See Section 3.13.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the Incident class are:

   purpose
      Required.  ENUM.  The purpose attribute describes the rationale
      for documenting the information in this class.  It is closely
      related to the Expectation class (Section 3.15).  These values are
      maintained in the "Incident-purpose" IANA registry per
      Section 10.2.  This attribute is defined as an enumerated list:

      1.  traceback.  The incident was sent for trace-back purposes.

      2.  mitigation.  The incident was sent to request aid in
          mitigating the described activity.

      3.  reporting.  The incident was sent to comply with reporting
          requirements.

      4.  watch.  The incident was sent to convey indicators that should
          be monitored.

      5.  other.  The incident was sent for purposes specified in the
          Expectation class.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-purpose
      Optional.  STRING.  A means by which to extend the purpose
      attribute.  See Section 5.1.1.

   status
      Optional.  ENUM.  The status attribute conveys the state in a
      workflow where the incident is currently found.  These values are
      maintained in the "Incident-status" IANA registry per
      Section 10.2.  This attribute is defined as an enumerated list:

      1.  new.  The incident is newly reported, and no action has been
          taken.

      2.  in-progress.  The incident is under investigation.

      3.  forwarded.  The incident has been forwarded to another party
          for handling.

      4.  resolved.  The investigation into the activity in this
          incident has concluded.

      5.  future.  The described activity has not yet been detected.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-status
      Optional.  STRING.  A means by which to extend the status
      attribute.  See Section 5.1.1.

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "private".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.3. Common Attributes

There are a number of recurring attributes used in the information
model. They are documented in this section.

3.3.1. restriction Attribute

   The restriction attribute indicates the disclosure guidelines to
   which the sender expects the recipient to adhere for the information
   represented in this class and its children.  This guideline provides
   no security since there are no technical means to ensure that the
   recipient of the document handles the information as the sender
   requested.

   The value of this attribute is logically inherited by the children of
   this class.  That is to say, the disclosure rules applied to this
   class also apply to its children.

   It is possible to set a granular disclosure policy, since all of the
   high-level classes (i.e., children of the Incident class) have a
   restriction attribute.  Therefore, a child can override the
   guidelines of a parent class, be it to restrict or relax the
   disclosure rules (e.g., a child has a weaker policy than an ancestor;
   or an ancestor has a weak policy, and the children selectively apply
   more rigid controls).  The implicit value of the restriction
   attribute for a class that did not specify one can be found in the
   closest ancestor that did specify a value.

   This attribute is defined as an enumerated value with a default value
   of "private".  Note that the default value of the restriction
   attribute is only defined in the context of the Incident class.  In
   other classes where this attribute is used, no default is specified.

   These values are maintained in the "Restriction" IANA registry per
   Section 10.2.

   1.   public.  The information can be freely distributed without
        restriction.

   2.   partner.  The information may be shared within a closed
        community of peers, partners, or affected parties, but cannot be
        openly published.

   3.   need-to-know.  The information may be shared only within the
        organization with individuals that have a need to know.

   4.   private.  The information may not be shared.

   5.   default.  The information can be shared according to an
        information disclosure policy pre-arranged by the communicating
        parties.

   6.   white.  Same as 'public'.

   7.   green.  Same as 'partner'.

   8.   amber.  Same as 'need-to-know'.

   9.   red.  Same as 'private'.

   10.  ext-value.  A value used to indicate that this attribute is
        extended and the actual value is provided using the
        corresponding ext-* attribute.  See Section 5.1.1.

3.3.2. observable-id Attribute

   The observable-id attribute tags information in the document as an
   observable so that it can be referenced later in the description of
   an indicator.  The value of this attribute is a unique identifier in
   the scope of the document.  It is used by the ObservableReference
   class to enumerate observables when defining an indicator with the
   IndicatorData class.

3.4. IncidentID Class

   The IncidentID class represents a tracking number that is unique in
   the context of the CSIRT.  It serves as an identifier for an incident
   or a document identifier when sharing indicators.  This identifier
   would serve as an index into a CSIRT's incident handling or knowledge
   management system.

   The combination of the name attribute and the string in the element
   content MUST be a globally unique identifier describing the activity.
   Documents generated by a given CSIRT MUST NOT reuse the same value
   unless they are referencing the same incident.

   +------------------------+
   | IncidentID             |
   +------------------------+
   | STRING                 |
   |                        |
   | STRING name            |
   | STRING instance        |
   | ENUM restriction       |
   | STRING ext-restriction |
   +------------------------+

                      Figure 7: The IncidentID Class

   The content of the class is an incident identifier of type STRING.

   The attributes of the IncidentID class are:

   name
      Required.  STRING.  An identifier describing the CSIRT that
      created the document.  In order to have a globally unique CSIRT
      name, the fully qualified domain name associated with the CSIRT
      MUST be used.

   instance
      Optional.  STRING.  An identifier referencing a subset of the
      named incident.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.5. AlternativeID Class

   The AlternativeID class lists the tracking numbers used by CSIRTs,
   other than the one generating the document, to refer to the identical
   activity described in the IODEF document.  A tracking number listed
   as an AlternativeID references the same incident detected by another
   CSIRT.  The tracking numbers of the CSIRT that generated the IODEF
   document must never be considered an AlternativeID.

   +------------------------+
   | AlternativeID          |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ IncidentID ]
   | STRING ext-restriction |
   +------------------------+

                     Figure 8: The AlternativeID Class

   The aggregate class of the AlternativeID class is:

   IncidentID
      One or more.  The tracking number of another CSIRT.  See
      Section 3.4.

   The attributes of the AlternativeID class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.6. RelatedActivity Class

   The RelatedActivity class relates the information described in the
   rest of the document to previously observed incidents or activity and
   allows attribution to a specific actor or campaign.

   +------------------------+
   | RelatedActivity        |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ IncidentID     ]
   | STRING ext-restriction |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ ThreatActor    ]
   |                        |<>--{0..*}--[ Campaign       ]
   |                        |<>--{0..*}--[ IndicatorID    ]
   |                        |<>--{0..1}--[ Confidence     ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                    Figure 9: The RelatedActivity Class

   The aggregate classes of the RelatedActivity class are:

   IncidentID
      Zero or more.  The tracking number of a related incident.  See
      Section 3.4.

   URL
      Zero or more.  URL.  A URL to activity related to this incident.

   ThreatActor
      Zero or more.  The threat actor to whom the incident activity is
      attributed.  See Section 3.7.

   Campaign
      Zero or more.  The campaign of a given threat actor to whom the
      described activity is attributed.  See Section 3.8.

   IndicatorID
      Zero or more.  A reference to a related indicator.  See
      Section 3.4.

   Confidence
      Zero or one.  An estimate of the confidence in attributing this
      RelatedActivity to the events described in the document.  See
      Section 3.12.5.

   Description
      Zero or more.  ML_STRING.  A description of how these
      relationships were derived.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The RelatedActivity class MUST have at least one instance of any of
   the following child classes: IncidentID, URL, ThreatActor, Campaign,
   Description, or AdditionalData.

   The attributes of the RelatedActivity class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.7. ThreatActor Class

   The ThreatActor class describes a threat actor.

   +------------------------+
   | ThreatActor            |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ ThreatActorID  ]
   | STRING ext-restriction |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                     Figure 10: The ThreatActor Class

   The aggregate classes of the ThreatActor class are:

   ThreatActorID
      Zero or more.  STRING.  An identifier for the threat actor.

   URL
      Zero or more.  URL.  A URL to a reference describing the threat
      actor.

   Description
      Zero or more.  ML_STRING.  A description of the threat actor.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The ThreatActor class MUST have at least one instance of a child
   class.

   The attributes of the ThreatActor class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.8. Campaign Class

   The Campaign class describes a campaign of attacks by a threat actor.

   +------------------------+
   | Campaign               |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ CampaignID     ]
   | STRING ext-restriction |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                       Figure 11: The Campaign Class

   The aggregate classes of the Campaign class are:

   CampaignID
      Zero or more.  STRING.  An identifier for the campaign.

   URL
      Zero or more.  URL.  A URL to a reference describing the campaign.

   Description
      Zero or more.  ML_STRING.  A description of the campaign.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The Campaign class MUST have at least one instance of a child class.

   The attributes of the Campaign class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.9. Contact Class

   The Contact class describes contact information for organizations and
   personnel involved in the incident.  This class allows for the naming
   of the involved party, specifying contact information for them, and
   identifying their role in the incident.

   People and organizations are treated interchangeably as contacts; one
   can be associated with the other using the recursive definition of
   the class (the Contact class is aggregated into the Contact class).
   The type attribute disambiguates the type of contact information
   being provided.

   The recursive definition of Contact provides a way to relate
   information without requiring the explicit use of identifiers or
   duplication of data.  A complete point of contact is derived by a
   particular traversal from the root Contact class to the leaf Contact
   class.  Each child Contact class logically inherits contact
   information from its ancestors.

   +------------------------+
   | Contact                |
   +------------------------+
   | ENUM role              |<>--{0..*}--[ ContactName    ]
   | STRING ext-role        |<>--{0..*}--[ ContactTitle   ]
   | ENUM type              |<>--{0..*}--[ Description    ]
   | STRING ext-type        |<>--{0..*}--[ RegistryHandle ]
   | ENUM restriction       |<>--{0..*}--[ PostalAddress  ]
   | STRING ext-restriction |<>--{0..*}--[ Email          ]
   |                        |<>--{0..*}--[ Telephone      ]
   |                        |<>--{0..1}--[ Timezone       ]
   |                        |<>--{0..*}--[ Contact        ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                       Figure 12: The Contact Class

   The aggregate classes of the Contact class are:

   ContactName
      Zero or more.  ML_STRING.  The name of the contact.  The contact
      may either be an organization or a person.  The type attribute
      disambiguates the semantics.

   ContactTitle
      Zero or more.  ML_STRING.  The title for the individual named in
      the ContactName.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      contact.

   RegistryHandle
      Zero or more.  A handle name into the registry of the contact.
      See Section 3.9.1.

   PostalAddress
      Zero or more.  The postal address of the contact.  See
      Section 3.9.2.

   Email
      Zero or more.  The email address of the contact.  See
      Section 3.9.3.

   Telephone
      Zero or more.  The telephone number of the contact.  See
      Section 3.9.4.

   Timezone
      Zero or one.  TIMEZONE.  The timezone in which the contact
      resides.

   Contact
      Zero or more.  A recursive definition of the Contact class.  This
      definition can be used to group common data pertaining to multiple
      points of contact and is especially useful when listing multiple
      contacts at the same organization.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   At least one of the aggregate classes MUST be present in an instance
   of the Contact class.

   The attributes of the Contact class are:

   role
      Required.  ENUM.  Indicates the role the contact fulfills.  These
      values are maintained in the "Contact-role" IANA registry per
      Section 10.2.

      1.   creator.  The entity that generates the document.

      2.   reporter.  The entity that reported the information.

      3.   admin.  An administrative contact or business owner for an
           asset or organization.

      4.   tech.  An entity responsible for the day-to-day management of
           technical issues for an asset or organization.

      5.   provider.  An external hosting provider for an asset.

      6.   user.  An end-user of an asset or part of an organization.

      7.   billing.  An entity responsible for billing issues for an
           asset or organization.

      8.   legal.  An entity responsible for legal issues related to an
           asset or organization.

      9.   irt.  An entity responsible for handling security issues for
           an asset or organization.

      10.  abuse.  An entity responsible for handling abuse originating
           from an asset or organization.

      11.  cc.  An entity that is to be kept informed about the events
           related to an asset or organization.

      12.  cc-irt.  A CSIRT or information-sharing organization
           coordinating activity related to an asset or organization.

      13.  leo.  A law enforcement organization supporting the
           investigation of activity affecting an asset or organization.

      14.  vendor.  The vendor that produces an asset.

      15.  vendor-support.  A vendor that provides services.

      16.  victim.  A victim in the incident.

      17.  victim-notified.  A victim in the incident who has been
           notified.

      18.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-role
      Optional.  STRING.  A means by which to extend the role attribute.
      See Section 5.1.1.

   type
      Required.  ENUM.  Indicates the type of contact being described.
      This attribute is defined as an enumerated list.  These values are
      maintained in the "Contact-type" IANA registry per Section 10.2.

      1.  person.  The information for this contact references an
          individual.

      2.  organization.  The information for this contact references an
          organization.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.9.1. RegistryHandle Class

   The RegistryHandle class represents a handle into an Internet
   registry or community-specific database.

   +---------------------+
   | RegistryHandle      |
   +---------------------+
   | STRING              |
   |                     |
   | ENUM registry       |
   | STRING ext-registry |
   +---------------------+

                    Figure 13: The RegistryHandle Class

   The content of the class is a handle into a registry of type STRING.

   The attributes of the RegistryHandle class are:

   registry
      Required.  ENUM.  The database to which the handle belongs.  These
      values are maintained in the "RegistryHandle-registry" IANA
      registry per Section 10.2.  The possible values are:

      1.  internic.  Internet Network Information Center

      2.  apnic.  Asia Pacific Network Information Center

      3.  arin.  American Registry for Internet Numbers

      4.  lacnic.  Latin American and Caribbean Internet Addresses
          Registry

      5.  ripe.  Reseaux IP Europeens

      6.  afrinic.  African Network Information Center

      7.  local.  A database local to the CSIRT

      8.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-registry
      Optional.  STRING.  A means by which to extend the registry
      attribute.  See Section 5.1.1.

3.9.2. PostalAddress Class

   The PostalAddress class specifies a postal address and associated
   annotation.

   +--------------------+
   | PostalAddress      |
   +--------------------+
   | ENUM type          |<>----------[ PAddress         ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                    Figure 14: The PostalAddress Class

   The aggregate classes of the PostalAddress class are:

   PAddress
      One.  POSTAL.  A postal address.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      address.

   The attributes of the PostalAddress class are:

   type
      Optional.  ENUM.  Categorizes the type of address described in the
      PAddress class.  These values are maintained in the
      "PostalAddress-type" IANA registry per Section 10.2.

      1.  street.  An address describing a physical location.

      2.  mailing.  An address to which correspondence should be sent.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.9.3. Email Class

   The Email class specifies an email address and associated annotation.

   +--------------------+
   | Email              |
   +--------------------+
   | ENUM type          |<>----------[ EmailTo          ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                        Figure 15: The Email Class

   The aggregate classes of the Email class are:

   EmailTo
      One.  EMAIL.  An email address.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      email address.

   The attributes of the Email class are:

   type
      Optional.  ENUM.  Categorizes the type of email address described
      in the EmailTo class.  These values are maintained in the "Email-
      type" IANA registry per Section 10.2.

      1.  direct.  An email address of an individual.

      2.  hotline.  An email address regularly monitored for operational
          purposes.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.9.4. Telephone Class

   The Telephone class describes a telephone number and associated
   annotation.

   +--------------------+
   | Telephone          |
   +--------------------+
   | ENUM type          |<>----------[ TelephoneNumber  ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                      Figure 16: The Telephone Class

   The aggregate classes of the Telephone class are:

   TelephoneNumber
      One.  PHONE.  A telephone number.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      phone number.

   The attributes of the Telephone class are:

   type
      Optional.  ENUM.  Categorizes the type of telephone number
      described in the TelephoneNumber class.  These values are
      maintained in the "Telephone-type" IANA registry per Section 10.2.

      1.  wired.  A number of a wire-line (land-line) phone.

      2.  mobile.  A number of a mobile phone.

      3.  fax.  A number to a fax machine.

      4.  hotline.  A number to a regularly monitored operational
          hotline.

      5.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.10. Discovery Class

   The Discovery class describes how an incident was detected.

   +------------------------+
   | Discovery              |
   +------------------------+
   | ENUM source            |<>--{0..*}--[ Description      ]
   | STRING ext-source      |<>--{0..*}--[ Contact          ]
   | ENUM restriction       |<>--{0..*}--[ DetectionPattern ]
   | STRING ext-restriction |
   +------------------------+

                      Figure 17: The Discovery Class

   The aggregate classes of the Discovery class are:

   Description
      Zero or more.  ML_STRING.  A free-form text description of how
      this incident was detected.

   Contact
      Zero or more.  Contact information for the party that discovered
      the incident.  See Section 3.9.

   DetectionPattern
      Zero or more.  Describes an application-specific configuration
      that detected the incident.  See Section 3.10.1.

   The attributes of the Discovery class are:

   source
      Optional.  ENUM.  Categorizes the techniques used to discover the
      incident.  These values are partially derived from Table 3-1 of
      [NIST800.61rev2].  These values are maintained in the "Discovery-
      source" IANA registry per Section 10.2.

      1.   nidps.  Network Intrusion Detection or Prevention System.

      2.   hips.  Host-based Intrusion Prevention System.

      3.   siem.  Security Information and Event Management System.

      4.   av.  Antivirus or antispam software.

      5.   third-party-monitoring.  Contracted third-party monitoring
           service.

      6.   incident.  The activity was discovered while investigating an
           unrelated incident.

      7.   os-log.  Operating system logs.

      8.   application-log.  Application logs.

      9.   device-log.  Network device logs.

      10.  network-flow.  Network flow analysis.

      11.  passive-dns.  Passive DNS analysis.

      12.  investigation.  Manual investigation initiated based on
           notification of a new vulnerability or exploit.

      13.  audit.  Security audit.

      14.  internal-notification.  A party within the organization
           reported the activity.

      15.  external-notification.  A party outside of the organization
           reported the activity.

      16.  leo.  A law enforcement organization notified the victim
           organization.

      17.  partner.  A customer or business partner reported the
           activity to the victim organization.

      18.  actor.  The threat actor directly or indirectly reported this
           activity to the victim organization.

      19.  unknown.  Unknown detection approach.

      20.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-source
      Optional.  STRING.  A means by which to extend the source
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.10.1. DetectionPattern Class

   The DetectionPattern class describes a configuration or signature
   that can be used by an Intrusion Detection System (IDS) / Intrusion
   Prevention System (IPS), SIEM, antivirus, endpoint protection,
   network analysis, malware analysis, or host forensics tool to
   identify a particular phenomenon.  This class requires the
   identification of the target application and allows the configuration
   to be described in either free form or machine-readable form.

   +------------------------+
   | DetectionPattern       |
   +------------------------+
   | ENUM restriction       |<>----------[ Application            ]
   | STRING ext-restriction |<>--{0..*}--[ Description            ]
   | ID observable-id       |<>--{0..*}--[ DetectionConfiguration ]
   +------------------------+

                   Figure 18: The DetectionPattern Class

   The aggregate classes of the DetectionPattern class are:

   Application
      One.  SOFTWARE.  The application for which the
      DetectionConfiguration or Description is being provided.

   Description
      Zero or more.  ML_STRING.  A free-form text description of how to
      use the information provided in the Application or
      DetectionConfiguration classes.

   DetectionConfiguration
      Zero or more.  STRING.  A machine-consumable configuration to find
      a pattern of activity.

   An instance of either the Description or DetectionConfiguration class
   MUST be present.

   The attributes of the DetectionPattern class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.11. Method Class

   The Method class describes the tactics, techniques, procedures, or
   weakness used by the threat actor in an incident.  This class
   consists of both a list of references describing the attack methods
   and weaknesses and a free-form text description.

   +------------------------+
   | Method                 |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ Reference         ]
   | STRING ext-restriction |<>--{0..*}--[ Description       ]
   |                        |<>--{0..*}--[ sci:AttackPattern ]
   |                        |<>--{0..*}--[ sci:Vulnerability ]
   |                        |<>--{0..*}--[ sci:Weakness      ]
   |                        |<>--{0..*}--[ AdditionalData    ]
   +------------------------+

                        Figure 19: The Method Class

   The aggregate classes of the Method class are:

   Reference
      Zero or more.  A reference to a vulnerability, malware sample,
      advisory, or analysis of an attack technique.  See Section 3.11.1.

   Description
      Zero or more.  ML_STRING.  A free-form text description of
      techniques, tactics, or procedures used by the threat actor.

   sci:AttackPattern
      Zero or more.  A reference to a pattern of attack or exploitation
      per [RFC7203].

   sci:Vulnerability
      Zero or more.  A reference to a vulnerability per [RFC7203].

   sci:Weakness
      Zero or more.  A reference to the exploited weakness per
      [RFC7203].

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   An instance of one of these children MUST be present.

   The attributes of the Method class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.11.1. Reference Class

   The Reference class is an external reference to relevant information
   such as a vulnerability, IDS alert, malware sample, advisory, or
   attack technique.

   +-------------------------+
   | Reference               |
   +-------------------------+
   | ID observable-id        |<>--{0..1}--[ enum:ReferenceName ]
   |                         |<>--{0..*}--[ URL                ]
   |                         |<>--{0..*}--[ Description        ]
   +-------------------------+

                      Figure 20: The Reference Class

   The aggregate classes of the Reference class are:

   enum:ReferenceName
      Zero or one.  Reference identifier per [RFC7495].

   URL
      Zero or more.  URL.  A URL to a reference.

   Description
      Zero or more.  ML_STRING.  A free-form text description of this
      reference.

   At least one of these classes MUST be present.

   The attribute of the Reference class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.12. Assessment Class

   The Assessment class describes the repercussions of the incident to
   the victim.

   +-------------------------+
   | Assessment              |
   +-------------------------+
   | ENUM occurrence         |<>--{0..*}--[ IncidentCategory ]
   | ENUM restriction        |<>--{0..*}--[ SystemImpact     ]
   | STRING ext-restriction  |<>--{0..*}--[ BusinessImpact   ]
   | ID observable-id        |<>--{0..*}--[ TimeImpact       ]
   |                         |<>--{0..*}--[ MonetaryImpact   ]
   |                         |<>--{0..*}--[ IntendedImpact   ]
   |                         |<>--{0..*}--[ Counter          ]
   |                         |<>--{0..*}--[ MitigatingFactor ]
   |                         |<>--{0..*}--[ Cause            ]
   |                         |<>--{0..1}--[ Confidence       ]
   |                         |<>--{0..*}--[ AdditionalData   ]
   +-------------------------+

                      Figure 21: The Assessment Class

   The aggregate classes of the Assessment class are:

   IncidentCategory
      Zero or more.  ML_STRING.  A free-form text description
      categorizing the type of incident.

   SystemImpact
      Zero or more.  A technical characterization of the impact of the
      incident activity on the victim's enterprise.  See Section 3.12.1.

   BusinessImpact
      Zero or more.  Impact of the incident activity on the business
      functions of the victim organization.  See Section 3.12.2.

   TimeImpact
      Zero or more.  A characterization of the victim organization due
      to the incident activity as a function of time.  See
      Section 3.12.3.

   MonetaryImpact
      Zero or more.  The financial loss due to the incident activity.
      See Section 3.12.4.

   IntendedImpact
      Zero or more.  The intended outcome to the victim sought by the
      threat actor.  Defined identically to the BusinessImpact defined
      in Section 3.12.2 but describes intent rather than the realized
      impact.

   Counter
      Zero or more.  A counter with which to summarize the magnitude of
      the activity.  See Section 3.18.3.

   MitigatingFactor
      Zero or more.  ML_STRING.  A description of a mitigating factor
      relative to the impact on the victim organization.

   Cause
      Zero or more.  ML_STRING.  A description of an underlying cause of
      the impact.

   Confidence
      Zero or one.  An estimate of confidence in the impact assessment.
      See Section 3.12.5.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   At least one instance of the possible five impact classes (i.e.,
   SystemImpact, BusinessImpact, TimeImpact, MonetaryImpact, or
   IntendedImpact) MUST be present.

   The attributes of the Assessment class are:

   occurrence
      Optional.  ENUM.  Specifies whether the assessment is describing
      actual or potential outcomes.

      1.  actual.  This assessment describes activity that has occurred.

      2.  potential.  This assessment describes potential activity that
          might occur.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.12.1. SystemImpact Class

   The SystemImpact class describes the technical impact of the incident
   to the systems on the network.

   +-----------------------+
   | SystemImpact          |
   +-----------------------+
   | ENUM severity         |<>--{0..*}--[ Description ]
   | ENUM completion       |
   | ENUM type             |
   | STRING ext-type       |
   +-----------------------+

                     Figure 22: The SystemImpact Class

   The aggregate class of the SystemImpact class is:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      impact to the system.

   The attributes of the SystemImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   completion
      Optional.  ENUM.  An indication whether the described activity was
      successful.  The permitted values are shown below.  There is no
      default value.

      1.  failed.  The attempted activity was not successful.

      2.  succeeded.  The attempted activity succeeded.

   type
      Required.  ENUM.  Classifies the impact.  The permitted values are
      shown below.  The default value is "unknown".  These values are
      maintained in the "SystemImpact-type" IANA registry per
      Section 10.2.

      1.   takeover-account.  Control was taken of a given account.

      2.   takeover-service.  Control was taken of a given service.

      3.   takeover-system.  Control was taken of a given system.

      4.   cps-manipulation.  A cyber-physical system was manipulated.

      5.   cps-damage.  A cyber-physical system was damaged.

      6.   availability-data.  Access to particular data was degraded or
           denied.

      7.   availability-account.  Access to an account was degraded or
           denied.

      8.   availability-service.  Access to a service was degraded or
           denied.

      9.   availability-system.  Access to a system was degraded or
           denied.

      10.  damaged-system.  Hardware on a system was irreparably
           damaged.

      11.  damaged-data.  Data on a system was deleted.

      12.  breach-proprietary.  Sensitive or proprietary information was
           accessed or exfiltrated.

      13.  breach-privacy.  Personally identifiable information was
           accessed or exfiltrated.

      14.  breach-credential.  Credential information was accessed or
           exfiltrated.

      15.  breach-configuration.  System configuration or data inventory
           was access or exfiltrated.

      16.  integrity-data.  Data on the system was modified.

      17.  integrity-configuration.  Application or system configuration
           was modified.

      18.  integrity-hardware.  Firmware of a hardware component was
           modified.

      19.  traffic-redirection.  Network traffic on the system was
           redirected

      20.  monitoring-traffic.  Network traffic emerging from a host or
           enclave was monitored.

21. monitoring-host. System activity (e.g., running processes,
keystrokes) were monitored.

22. policy. Activity violated the system owner's acceptable use
policy.

23. unknown. The impact is unknown.

      24.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.12.2. BusinessImpact Class

   The BusinessImpact class describes and characterizes the degree to
   which the function of the organization was impacted by the incident.

   +-------------------------+
   | BusinessImpact          |
   +-------------------------+
   | ENUM severity           |<>--{0..*}--[ Description ]
   | STRING ext-severity     |
   | ENUM type               |
   | STRING ext-type         |
   +-------------------------+

                    Figure 23: The BusinessImpact Class

   The aggregate class of the BusinessImpact class is:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      impact to the organization.

   The attributes of the BusinessImpact class are:

   severity
      Optional.  ENUM.  Characterizes the severity of the incident on
      business functions.  The permitted values are shown below.  They
      were derived from Table 3-2 of [NIST800.61rev2].  The default
      value is "unknown".  These values are maintained in the
      "BusinessImpact-severity" IANA registry per Section 10.2.

      1.  none.  No effect to the organization's ability to provide all
          services to all users.

      2.  low.  Minimal effect as the organization can still provide all
          critical services to all users but has lost efficiency.

      3.  medium.  The organization has lost the ability to provide a
          critical service to a subset of system users.

      4.  high.  The organization is no longer able to provide some
          critical services to any users.

      5.  unknown.  The impact is not known.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-severity
      Optional.  STRING.  A means by which to extend the severity
      attribute.  See Section 5.1.1.

   type
      Required.  ENUM.  Characterizes the effect this incident had on
      the business.  The permitted values are shown below.  The default
      value is "unknown".  These values are maintained in the
      "BusinessImpact-type" IANA registry per Section 10.2.

      1.   breach-proprietary.  Sensitive or proprietary information was
           accessed or exfiltrated.

      2.   breach-privacy.  Personally identifiable information was
           accessed or exfiltrated.

      3.   breach-credential.  Credential information was accessed or
           exfiltrated.

      4.   loss-of-integrity.  Sensitive or proprietary information was
           changed or deleted.

      5.   loss-of-service.  Service delivery was disrupted.

      6.   theft-financial.  Money was stolen.

      7.   theft-service.  Services were misappropriated.

      8.   degraded-reputation.  The reputation of the organization's
           brand was diminished.

      9.   asset-damage.  A cyber-physical system was damaged.

      10.  asset-manipulation.  A cyber-physical system was manipulated.

      11.  legal.  The incident resulted in legal or regulatory action.

      12.  extortion.  The incident resulted in actors extorting the
           victim organization.

      13.  unknown.  The impact is unknown.

      14.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.12.3. TimeImpact Class

   The TimeImpact class describes the impact of the incident on an
   organization as a function of time.  It provides a way to convey down
   time and recovery time.

   +---------------------+
   | TimeImpact          |
   +---------------------+
   | REAL                |
   |                     |
   | ENUM severity       |
   | ENUM metric         |
   | STRING ext-metric   |
   | ENUM duration       |
   | STRING ext-duration |
   +---------------------+

                      Figure 24: The TimeImpact Class

   The content of the class is of type REAL and specifies an amount of
   time.  The duration attribute provides units for this content, and
   the metric attribute explains what this content is measuring.

   The attributes of the TimeImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   metric
      Required.  ENUM.  Defines the meaning of the value in the element
      content.  These values are maintained in the "TimeImpact-metric"
      IANA registry per Section 10.2.

      1.  labor.  Total staff time to recovery from the activity (e.g.,
          2 employees working 4 hours each would be 8 hours).

      2.  elapsed.  Elapsed time from the beginning of the recovery to
          its completion (i.e., wall-clock time).

      3.  downtime.  Duration of time for which some provided service(s)
          was not available.

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-metric
      Optional.  STRING.  A means by which to extend the metric
      attribute.  See Section 5.1.1.

   duration
      Optional.  ENUM.  Defines the unit of time for the value in the
      element content.  The default value is "hour".  These values are
      maintained in the "TimeImpact-duration" IANA registry per
      Section 10.2.

      1.  second.  The unit of the element content is seconds.

      2.  minute.  The unit of the element content is minutes.

      3.  hour.  The unit of the element content is hours.

      4.  day.  The unit of the element content is days.

      5.  month.  The unit of the element content is months.

      6.  quarter.  The unit of the element content is quarters.

      7.  year.  The unit of the element content is years.

      8.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-duration
      Optional.  STRING.  A means by which to extend the duration
      attribute.  See Section 5.1.1.

3.12.4. MonetaryImpact Class

   The MonetaryImpact class describes the financial impact of the
   activity on an organization.  For example, this impact may consider
   losses due to the cost of the investigation or recovery, diminished
   productivity of the staff, or a tarnished reputation that will affect
   future opportunities.

   +------------------+
   | MonetaryImpact   |
   +------------------+
   | REAL             |
   |                  |
   | ENUM severity    |
   | STRING currency  |
   +------------------+

                    Figure 25: The MonetaryImpact Class

   The content of the class is of type REAL and specifies a quantity of
   money.  The currency attribute defines the currency of this value.

   The attributes of the MonetaryImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   currency
      Optional.  STRING.  Defines the currency in which the value in the
      element content is expressed.  The permitted values are defined in
      "Codes for the representation of currencies" [ISO4217].  There is
      no default value.

3.12.5. Confidence Class

   The Confidence class represents an estimate of the validity and
   accuracy of data expressed in the document.  This estimate can be
   expressed as a category or a numeric calculation.

   +-------------------+
   | Confidence        |
   +-------------------+
   | REAL              |
   |                   |
   | ENUM rating       |
   | STRING ext-rating |
   +-------------------+

                      Figure 26: The Confidence Class

   The content of the class is of type REAL and specifies a numerical
   assessment in the confidence of the data when the value of the rating
   attribute is "numeric".  Otherwise, this element MUST be empty.

   The attributes of the Confidence class are:

   rating
      Required.  ENUM.  A qualitative assessment of confidence.  These
      values are maintained in the "Confidence-rating" IANA registry per
      Section 10.2

      1.  low.  Low confidence.

      2.  medium.  Medium confidence.

      3.  high.  High confidence.

      4.  numeric.  The element content contains a number that conveys
          the confidence of the data.  The semantics of this number is
          outside the scope of this specification.

      5.  unknown.  The confidence rating value is not known.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-rating
      Optional.  STRING.  A means by which to extend the rating
      attribute.  See Section 5.1.1.

3.13. History Class

   The History class is a log of the significant events or actions
   performed by the involved parties during the course of handling the
   incident.

   The level of detail maintained in this log is left up to the
   discretion of those handling the incident.

   +------------------------+
   | History                |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ HistoryItem ]
   | STRING ext-restriction |
   +------------------------+

                       Figure 27: The History Class

   The aggregate classes of the History class are:

   HistoryItem
      One or more.  An entry in the history log of significant events or
      actions performed by the involved parties.  See Section 3.13.1.

   The attributes of the History class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.13.1. HistoryItem Class

   The HistoryItem class is an entry in the History (Section 3.13) log
   that documents a particular action or event that occurred in the
   course of handling the incident.  The details of the entry are a
   free-form text description, but each can be categorized with the type
   attribute.

   +-------------------------+
   | HistoryItem             |
   +-------------------------+
   | ENUM action             |<>----------[ DateTime       ]
   | STRING ext-action       |<>--{0..1}--[ IncidentID     ]
   | ENUM restriction        |<>--{0..1}--[ Contact        ]
   | STRING ext-restriction  |<>--{0..*}--[ Description    ]
   | ID observable-id        |<>--{0..*}--[ DefinedCOA     ]
   |                         |<>--{0..*}--[ AdditionalData ]
   +-------------------------+

                     Figure 28: The HistoryItem Class

   The aggregate classes of the HistoryItem class are:

   DateTime
      One.  DATETIME.  A timestamp of this entry in the history log.

   IncidentID
      Zero or one.  In a history log created by multiple parties, the
      IncidentID provides a mechanism to specify which CSIRT created a
      particular entry and references this organization's tracking
      number.  When a single organization is maintaining the log, this
      class can be ignored.  See Section 3.4.

   Contact
      Zero or one.  Provides contact information for the entity that
      performed the action documented in this class.  See Section 3.9.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      action or event.

   DefinedCOA
      Zero or more.  STRING.  An identifier meaningful to the sender and
      recipient of this document that references a course of action
      (COA).  This class MUST be present if the action attribute is set
      to "defined-coa".

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The attributes of the HistoryItem class are:

   action
      Required.  ENUM.  Classifies a performed action or occurrence
      documented in this history log entry.  As activity will likely
      have been instigated either through a previously conveyed
      expectation or through an internal investigation, this attribute
      is identical to the action attribute of the Expectation class.
      The difference is only one of tense.  When an action is in this
      class, it has been completed.  See Section 3.15.

   ext-action
      Optional.  STRING.  A means by which to extend the action
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.14. EventData Class

   The EventData class is a container class to organize data about
   events that occurred during an incident.

   +-------------------------+
   | EventData               |
   +-------------------------+
   | ENUM restriction        |<>--{0..*}--[ Description    ]
   | STRING ext-restriction  |<>--{0..1}--[ DetectTime     ]
   | ID observable-id        |<>--{0..1}--[ StartTime      ]
   |                         |<>--{0..1}--[ EndTime        ]
   |                         |<>--{0..1}--[ RecoveryTime   ]
   |                         |<>--{0..1}--[ ReportTime     ]
   |                         |<>--{0..*}--[ Contact        ]
   |                         |<>--{0..*}--[ Discovery      ]
   |                         |<>--{0..1}--[ Assessment     ]
   |                         |<>--{0..*}--[ Method         ]
   |                         |<>--{0..*}--[ Flow           ]
   |                         |<>--{0..*}--[ Expectation    ]
   |                         |<>--{0..1}--[ Record         ]
   |                         |<>--{0..*}--[ EventData      ]
   |                         |<>--{0..*}--[ AdditionalData ]
   +-------------------------+

                      Figure 29: The EventData Class

   The aggregate classes of the EventData class are:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      event.

   DetectTime
      Zero or one.  DATETIME.  The time the event was detected.

   StartTime
      Zero or one.  DATETIME.  The time the event started.

   EndTime
      Zero or one.  DATETIME.  The time the event ended.

   RecoveryTime
      Zero or one.  DATETIME.  The time the site recovered from the
      event.

   ReportTime
      Zero or one.  DATETIME.  The time the event was reported.

   Contact
      Zero or more.  Contact information for the parties involved in the
      event.  See Section 3.9.

   Discovery
      Zero or more.  The means by which the event was detected.  See
      Section 3.10.

   Assessment
      Zero or one.  The impact of the event on the victim and the
      actions taken.  See Section 3.12.

   Method
      Zero or more.  The technique used by the threat actor in the
      event.  See Section 3.11.

   Flow
      Zero or more.  A description of the systems or networks involved.
      See Section 3.16.

   Expectation
      Zero or more.  The expected action to be performed by the
      recipient for the described event.  See Section 3.15.

   Record
      Zero or one.  Supportive data (e.g., log files) that provides
      additional information about the event.  See Section 3.22.

   EventData
      Zero or more.  A recursive definition of the EventData class.  See
      Section 3.14.2 for an explanation on using this class.

   AdditionalData
      Zero or more.  EXTENSION.  An extension mechanism for data not
      explicitly represented in the data model.

   At least one of the aggregate classes MUST be present in an instance
   of the EventData class.

   The attributes of the EventData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "default".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

observable-id
Optional. ID. See Section 3.3.2.

3.14.1. Relating the Incident and EventData Classes

   There is substantial overlap in the child classes aggregated in the
   Incident and EventData classes.  Nevertheless, the semantics of these
   classes are quite different.  The Incident class provides summary
   information about the entire incident, while the EventData class
   provides information about the individual events comprising the
   incident.  In the common case, the EventData class will provide more
   specific information for the general description provided in the
   Incident class.  However, in the case where the summarized
   information in the Incident class conflicts with the detailed
   information in an EventData class, the more specific EventData class
   MUST supersede the more generic information provided in the Incident
   class.

3.14.2. Recursive Definition of EventData

   The EventData class is a container for the properties of an event in
   an incident.  These properties include: the hosts involved, impact of
   the incident activity on the hosts, forensic logs, etc.  The
   recursive definition of EventData allows for the grouping of related
   information with common properties.  This approach eliminates the
   need for explicit identifiers to relate information or duplicate it.
   Instead, the relative depth (nesting) of a class is used to group
   (relate) information.

   For example, consider a case where two hosts experience different
   impacts during an incident.  However, these two hosts have common
   contact information.  A depiction of how this situation would be
   represented can be found in Figure 30.  EventData (2) and (3) group
   each of the two hosts with their unique impact.  EventData (1)
   describes the common Contact class these two hosts share.

3.15. Expectation Class

   The Expectation class conveys to the recipient of the IODEF document
   the actions the sender is requesting.

   +-------------------------+
   | Expectation             |
   +-------------------------+
   | ENUM action             |<>--{0..*}--[ Description ]
   | STRING ext-action       |<>--{0..*}--[ DefinedCOA  ]
   | ENUM severity           |<>--{0..1}--[ StartTime   ]
   | ENUM restriction        |<>--{0..1}--[ EndTime     ]
   | STRING ext-restriction  |<>--{0..1}--[ Contact     ]
   | ID observable-id        |
   +-------------------------+

                     Figure 31: The Expectation Class

   The aggregate classes of the Expectation class are:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      desired action(s).

   DefinedCOA
      Zero or more.  STRING.  A unique identifier meaningful to the
      sender and recipient of this document that references a course of
      action.  This class MUST be present if the action attribute is set
      to "defined-coa".

   StartTime
      Zero or one.  DATETIME.  The time at which the sender would like
      the action performed.  A timestamp that is earlier than the
      ReportTime specified in the Incident class denotes that the sender
      would like the action performed as soon as possible.  The absence
      of this element indicates no expectations of when the recipient
      would like the action performed.

   EndTime
      Zero or one.  DATETIME.  The time by which the sender expects the
      recipient to complete the action.  If the recipient cannot
      complete the action before EndTime, the recipient MUST NOT carry
      out the action.  Because of transit delays and clock drift, the
      sender MUST be prepared for the recipient to have carried out the
      action, even if it completes past EndTime.

   Contact
      Zero or one.  The entity expected to perform the action.  See
      Section 3.9.

   The attributes of the Expectation class are:

   action
      Optional.  ENUM.  Classifies the type of action requested.  The
      default value of "other".  These values are maintained in the
      "Expectation-action" IANA registry per Section 10.2.

      1.   nothing.  No action is requested.  Do nothing with the
           information.

      2.   contact-source-site.  Contact the site(s) identified as the
           source of the activity.

      3.   contact-target-site.  Contact the site(s) identified as the
           target of the activity.

      4.   contact-sender.  Contact the originator of the document.

      5.   investigate.  Investigate the system(s) listed in the event.

      6.   block-host.  Block traffic from the machine(s) listed as
           sources in the event.

      7.   block-network.  Block traffic from the network(s) lists as
           sources in the event.

      8.   block-port.  Block the port listed as sources in the event.

      9.   rate-limit-host.  Rate-limit the traffic from the machine(s)
           listed as sources in the event.

      10.  rate-limit-network.  Rate-limit the traffic from the
           network(s) lists as sources in the event.

      11.  rate-limit-port.  Rate-limit the port(s) listed as sources in
           the event.

      12.  redirect-traffic.  Redirect traffic from the intended
           recipient for further analysis.

      13.  honeypot.  Redirect traffic from systems listed in the event
           to a honeypot for further analysis.

      14.  upgrade-software.  Upgrade or patch the software or firmware
           on an asset listed in the event.

      15.  rebuild-asset.  Reinstall the operating system or
           applications on an asset listed in the event.

      16.  harden-asset.  Change the configuration of an asset listed in
           the event to reduce the attack surface.

      17.  remediate-other.  Remediate the activity in a way other than
           by rate-limiting or blocking.

      18.  status-triage.  Confirm receipt and begin triaging the
           incident.

      19.  status-new-info.  Notify the sender when new information is
           received for this incident.

      20.  watch-and-report.  Watch for the described activity or
           indicators, and notify the sender when seen.

      21.  training.  Train user to identify or mitigate the described
           threat.

      22.  defined-coa.  Perform a predefined course of action (COA).
           The COA is named in the DefinedCOA class.

      23.  other.  Perform a custom action described in the Description
           class.

      24.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-action
      Optional.  STRING.  A means by which to extend the action
      attribute.  See Section 5.1.1.

   severity
      Optional.  ENUM.  Indicates the desired priority of the action.
      This attribute is an enumerated list with no default value, and
      the semantics of these relative measures are context dependent.

      1.  low.  Low priority

      2.  medium.  Medium priority

      3.  high.  High priority

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "default".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.16. Flow Class

   The Flow class describes the systems and networks involved in the
   incident and the relationships between them.

   +------------------+
   | Flow             |
   +------------------+
   |                  |<>--{1..*}--[ System   ]
   +------------------+

                         Figure 32: The Flow Class

   The aggregate class of the Flow class is:

   System
      One or More.  A host or network involved in an event.  See
      Section 3.17.

   The Flow class has no attributes.

3.17. System Class

   The System class describes a system or network involved in an event.

   +------------------------+
   | System                 |
   +------------------------+
   | ENUM category          |<>----------[ Node            ]
   | STRING ext-category    |<>--{0..*}--[ NodeRole        ]
   | STRING interface       |<>--{0..*}--[ Service         ]
   | ENUM spoofed           |<>--{0..*}--[ OperatingSystem ]
   | ENUM virtual           |<>--{0..*}--[ Counter         ]
   | ENUM ownership         |<>--{0..*}--[ AssetID         ]
   | STRING ext-ownership   |<>--{0..*}--[ Description     ]
   | ENUM restriction       |<>--{0..*}--[ AdditionalData  ]
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                        Figure 33: The System Class

   The aggregate classes of the System class are:

   Node
      One.  A host or network involved in the incident.  See
      Section 3.18.

   NodeRole
      Zero or more.  The intended purpose of the system.  See
      Section 3.18.2.

   Service
      Zero or more.  A network service running on the system.  See
      Section 3.20.

   OperatingSystem
      Zero or more.  SOFTWARE.  The operating system running on the
      system.

   Counter
      Zero or more.  A counter with which to summarize properties of
      this host or network.  See Section 3.18.3.

   AssetID
      Zero or more.  STRING.  An asset identifier for the System.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      System.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The attributes of the System class are:

   category
      Optional.  ENUM.  Classifies the role the host or network played
      in the incident.  These values are maintained in the "System-
      category" IANA registry per Section 10.2.

      1.  source.  The System was the source of the event.

      2.  target.  The System was the target of the event.

      3.  intermediate.  The System was an intermediary in the event.

      4.  sensor.  The System was a sensor monitoring the event.

      5.  infrastructure.  The System was an infrastructure node of the
          IODEF document exchange.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

   interface
      Optional.  STRING.  Specifies the interface on which the event(s)
      on this System originated.  If the Node class specifies a network
      rather than a host, this attribute has no meaning.

   spoofed
      Optional.  ENUM.  An indication of confidence in whether this
      System was the true target or attacking host.  The permitted
      values for this attribute are shown below.  The default value is
      "unknown".

      1.  unknown.  The accuracy of the category attribute value is
          unknown.

      2.  yes.  The category attribute value is likely incorrect.  In
          the case of a source, the System is likely a decoy; with a
          target, the System was likely not the intended victim.

      3.  no.  The category attribute value is believed to be correct.

   virtual
      Optional.  ENUM.  Indicates whether this System is a virtual or
      physical device.  The default value is "unknown".

      1.  yes.  The System is a virtual device.

      2.  no.  The System is a physical device.

      3.  unknown.  It is not known if the System is virtual.

   ownership
      Optional.  ENUM.  Describes the ownership of this System relative
      to the victim in the incident.  These values are maintained in the
      "System-ownership" IANA registry per Section 10.2.

      1.  organization.  Corporate or enterprise owned.

      2.  personal.  Personally owned by an employee or affiliate of the
          corporation or enterprise.

      3.  partner.  Owned by a partner of the corporation or enterprise.

      4.  customer.  Owned by a customer of the corporation or
          enterprise.

      5.  no-relationship.  Owned by an entity that has no known
          relationship with the victim organization.

      6.  unknown.  Ownership is unknown.

      7.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-ownership
      Optional.  STRING.  A means by which to extend the ownership
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.18. Node Class

   The Node class identifies a system, asset, or network and its
   location.

   +---------------+
   | Node          |
   +---------------+
   |               |<>--{0..*}--[ DomainData    ]
   |               |<>--{0..*}--[ Address       ]
   |               |<>--{0..1}--[ PostalAddress ]
   |               |<>--{0..*}--[ Location      ]
   |               |<>--{0..*}--[ Counter       ]
   +---------------+

                         Figure 34: The Node Class

   The aggregate classes of the Node class are:

   DomainData
      Zero or more.  The domain (DNS) information associated with this
      node.  If an Address is not provided, at least one DomainData MUST
      be specified.  See Section 3.19.

   Address
      Zero or more.  The hardware, network, or application address of
      the node.  If a DomainData is not provided, at least one Address
      MUST be specified.  See Section 3.18.1.

   PostalAddress
      Zero or one.  POSTAL.  The postal address of the node.

   Location
      Zero or more.  ML_STRING.  A free-form text description of the
      physical location of the node.  This description may provide a
      more detailed description of where at the address specified by the
      PostalAddress class this node is found (e.g., room number, rack
      number, or slot number in a chassis).

   Counter
      Zero or more.  A counter with which to summarize properties of
      this host or network.  See Section 3.18.3.

   The Node class has no attributes.

3.18.1. Address Class

   The Address class represents a hardware (Layer 2), network (Layer 3),
   or application (Layer 7) address.

   +-------------------------+
   | Address                 |
   +-------------------------+
   | STRING                  |
   |                         |
   | ENUM category           |
   | STRING ext-category     |
   | STRING vlan-name        |
   | INTEGER vlan-num        |
   | ID observable-id        |
   +-------------------------+

                       Figure 35: The Address Class

   The content of the class is an address of type STRING whose semantics
   are determined by the category attribute.

   The attributes of the Address class are:

   category
      Required.  ENUM.  The type of address represented.  The default
      value is "ipv6-addr".  These values are maintained in the
      "Address-category" IANA registry per Section 10.2.

      1.   asn.  Autonomous System Number.

      2.   atm.  Asynchronous Transfer Mode (ATM) address.

      3.   e-mail.  Email address, per the EMAIL data type.

      4.   ipv4-addr.  IPv4 host address in dotted-decimal notation
           (i.e., a.b.c.d).

      5.   ipv4-net.  IPv4 network address in dotted-decimal notation,
           slash, significant bits (i.e., a.b.c.d/nn).

      6.   ipv4-net-masked.  A sanitized IPv4 address with significant
           bits per "ipv4-net" but with the character 'x' replacing any
           digit(s) in the address or prefix.

      7.   ipv4-net-mask.  IPv4 network address in dotted-decimal
           notation, slash, network mask in dotted-decimal notation
           (i.e., a.b.c.d/w.x.y.z).

      8.   ipv6-addr.  IPv6 host address per Section 4 of [RFC5952].

      9.   ipv6-net.  IPv6 network address, slash, prefix per
           Section 2.3 of [RFC4291].

      10.  ipv6-net-masked.  A sanitized IPv6 address and prefix per
           "ipv6-net" but with the character 'x' replacing any
           hexadecimal digit(s) in the address or digit(s) in the
           prefix.

      11.  mac.  Media Access Control (MAC) address (i.e.,
           aa:bb:cc:dd:ee:ff).

      12.  site-uri.  A URL or URI for a resource, per the URL data
           type.

      13.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

   vlan-name
      Optional.  STRING.  The name of the Virtual LAN to which the
      address belongs.

   vlan-num
      Optional.  INTEGER.  The number of the Virtual LAN to which the
      address belongs.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.18.2. NodeRole Class

The NodeRole class describes the function performed by or role of a
particular system, asset, or network.

   +-----------------------+
   | NodeRole              |
   +-----------------------+
   | ENUM category         |<>--{0..*}--[ Description ]
   | STRING ext-category   |
   +-----------------------+

                       Figure 36: The NodeRole Class

   The aggregate class of the NodeRole class is:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      role of the system.

   The attributes of the NodeRole class are:

   category
      Required.  ENUM.  Function or role of a node.  These values are
      maintained in the "NodeRole-category" IANA registry per
      Section 10.2.

      1.   client.  Client computer.

      2.   client-enterprise.  Client computer on the enterprise
           network.

      3.   client-partner.  Client computer on network of a partner.

      4.   client-remote.  Client computer remotely connected to the
           enterprise network.

      5.   client-kiosk.  Client computer serving as a kiosk.

      6.   client-mobile.  Mobile device.

      7.   server-internal.  Server with internal services.

      8.   server-public.  Server with public services.

      9.   www.  WWW server.

      10.  mail.  Mail server.

      11.  webmail.  Web mail server.

      12.  messaging.  Messaging server (e.g., NNTP, IRC, IM).

      13.  streaming.  Streaming-media server.

      14.  voice.  Voice server (e.g., SIP, H.323).

      15.  file.  File server.

      16.  ftp.  FTP server.

      17.  p2p.  Peer-to-peer node.

      18.  name.  Name server (e.g., DNS, WINS).

      19.  directory.  Directory server (e.g., LDAP, finger, whois).

      20.  credential.  Credential server (e.g., domain controller,
           Kerberos).

      21.  print.  Print server.

      22.  application.  Application server.

      23.  database.  Database server.

24. backup. Backup server.

25. dhcp. DHCP server.

26. assessment. Assessment server (e.g., vulnerability scanner,
endpoint assessment).

27. source-control. Source code control server.

28. config-management. Configuration management server.

29. monitoring. Security monitoring server (e.g., IDS).

30. infra. Infrastructure server (e.g., router, firewall, DHCP).

31. infra-firewall. Firewall.

32. infra-router. Router.

33. infra-switch. Switch.

34. camera. Camera and video system.

35. proxy. Proxy server.

36. remote-access. Remote access server.

37. log. Log server (e.g., syslog).

38. virtualization. Server running virtual machines.

39. pos. Point-of-sale device.

40. scada. Supervisory control and data acquisition (SCADA)
system.

41. scada-supervisory. Supervisory system for a SCADA.

42. sinkhole. Traffic sinkhole destination.

43. honeypot. Honeypot server.

44. anonymization. Anonymization server (e.g., Tor node).

45. c2-server. Malicious command and control server.

46. malware-distribution. Server that distributes malware

47. drop-server. Server to which exfiltrated content is
uploaded.

48. hop-point. Intermediary server used to get to a victim.

49. reflector. A system used in a reflector attack.

50. phishing-site. Site hosting phishing content.

51. spear-phishing-site. Site hosting spear-phishing content.

52. recruiting-site. Site to recruit.

53. fraudulent-site. Fraudulent site.

      54.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

3.18.3. Counter Class

   The Counter class summarizes multiple occurrences of an event or
   conveys counts or rates of various features.

   The complete semantics of this class are context dependent based on
   the class in which it is aggregated.

   +---------------------+
   | Counter             |
   +---------------------+
   | REAL                |
   |                     |
   | ENUM type           |
   | STRING ext-type     |
   | ENUM unit           |
   | STRING ext-unit     |
   | STRING meaning      |
   | ENUM duration       |
   | STRING ext-duration |
   +---------------------+

                       Figure 37: The Counter Class

   The content of the class is a value of type REAL whose meaning and
   units are determined by the type and duration attributes,
   respectively.  If the duration attribute is present, the element
   content is a rate.  Otherwise, it is a simple counter.

   The attributes of the Counter class are:

   type
      Required.  ENUM.  Specifies the type of counter specified in the
      element content.  These values are maintained in the "Counter-
      type" IANA registry per Section 10.2.

      1.  count.  The Counter class value is a counter.

      2.  peak.  The Counter class value is a peak value.

      3.  average.  The Counter class value is an average.

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   unit
      Required.  ENUM.  Specifies the units of the element content.
      These values are maintained in the "Counter-unit" IANA registry
      per Section 10.2.

      1.   byte.  Bytes transferred.

      2.   mbit.  Megabits (Mbits) transferred.

      3.   packet.  Packets.

      4.   flow.  Network flow records.

      5.   session.  Sessions.

      6.   alert.  Notifications generated by another system (e.g., IDS
           or SIEM system).

      7.   message.  Messages (e.g., mail messages).

      8.   event.  Events.

      9.   host.  Hosts.

      10.  site.  Site.

      11.  organization.  Organizations.

      12.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-unit
      Optional.  STRING.  A means by which to extend the unit attribute.
      See Section 5.1.1.

   meaning
      Optional.  STRING.  A free-form text description of the metric
      represented by the Counter.

   duration
      Optional.  ENUM.  If present, the Counter class represents a rate.
      This attribute specifies a unit of time over which the rate whose
      units are specified in the unit attribute is being conveyed.  This
      attribute is the denominator of the rate (where the unit attribute
      specified the nominator).  The possible values of this attribute
      are defined in the duration attribute of Section 3.12.3

   ext-duration
      Optional.  STRING.  A means by which to extend the duration
      attribute.  See Section 5.1.1.

3.19. DomainData Class

   The DomainData class describes a domain name and metadata associated
   with this domain.

   +--------------------------+
   | DomainData               |
   +--------------------------+
   | ENUM system-status       |<>----------[ Name                 ]
   | STRING ext-system-status |<>--{0..1}--[ DateDomainWasChecked ]
   | ENUM domain-status       |<>--{0..1}--[ RegistrationDate     ]
   | STRING ext-domain-status |<>--{0..1}--[ ExpirationDate       ]
   | ID observable-id         |<>--{0..*}--[ RelatedDNS           ]
   |                          |<>--{0..*}--[ Nameservers          ]
   |                          |<>--{0..1}--[ DomainContacts       ]
   +--------------------------+

                      Figure 38: The DomainData Class

   The aggregate classes of the DomainData class are:

   Name
      One.  STRING.  The domain name of a system.

   DateDomainWasChecked
      Zero or one.  DATETIME.  A timestamp of when the domain listed in
      the Name class was resolved.

   RegistrationDate
      Zero or one.  DATETIME.  A timestamp of when domain listed in the
      Name class was registered.

   ExpirationDate
      Zero or one.  DATETIME.  A timestamp of when the domain listed in
      the Name class is set to expire.

   RelatedDNS
      Zero or more.  EXTENSION.  Additional DNS records associated with
      this domain.

   Nameservers
      Zero or more.  The nameservers identified for the domain listed in
      the Name class.  See Section 3.19.1.

   DomainContacts
      Zero or one.  Contact information for the domain listed in the
      Name class supplied by the registrar or through a whois query.

   The attributes of the DomainData class are:

   system-status
      Required.  ENUM.  Assesses the domain's involvement in the event.
      These values are maintained in the "DomainData-system-status" IANA
      registry per Section 10.2.

      1.  spoofed.  This domain was spoofed.

      2.  fraudulent.  This domain was operated with fraudulent
          intentions.

      3.  innocent-hacked.  This domain was compromised by a third
          party.

      4.  innocent-hijacked.  This domain was deliberately hijacked.

      5.  unknown.  No categorization for this domain known.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-system-status
      Optional.  STRING.  A means by which to extend the system-status
      attribute.  See Section 5.1.1.

   domain-status
      Required.  ENUM.  Categorizes the registry status of the domain at
      the time the document was generated.  These values and their
      associated descriptions are derived from Section 3.2.2 of
      [RFC3982].  These values are maintained in the
      "DomainData-domain-status" IANA registry per Section 10.2.

      1.   reservedDelegation.  The domain is permanently inactive.

      2.   assignedAndActive.  The domain is in a normal state.

      3.   assignedAndInactive.  The domain has an assigned
           registration, but the delegation is inactive.

      4.   assignedAndOnHold.  The domain is in dispute.

      5.   revoked.  The domain is in the process of being purged from
           the database.

      6.   transferPending.  The domain is pending a change in
           authority.

      7.   registryLock.  The domain is on hold by the registry.

      8.   registrarLock.  Same as "registryLock".

      9.   other.  The domain has a known status, but it is not one of
           the redefined enumerated values.

      10.  unknown.  The domain has an unknown status.

      11.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-domain-status
      Optional.  STRING.  A means by which to extend the domain-status
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.19.1. Nameservers Class

   The Nameservers class describes the nameservers associated with a
   given domain.

   +--------------------+
   | Nameservers        |
   +--------------------+
   |                    |<>----------[ Server  ]
   |                    |<>--{1..*}--[ Address ]
   +--------------------+

                     Figure 39: The Nameservers Class

   The aggregate classes of the Nameservers class are:

   Server
      One.  STRING.  The domain name of the nameserver.

   Address
      One or more.  The address of the nameserver.  The value of the
      category attribute MUST be either "ipv4-addr" or "ipv6-addr".  See
      Section 3.18.1.

   The Nameservers class has no attributes.

3.19.2. DomainContacts Class

   The DomainContacts class describes the contact information for a
   given domain provided either by the registrar or through a whois
   query.

   This contact information can be explicitly described through a
   Contact class, or a reference can be provided to a domain with
   identical contact information.  Either a single SameDomainContact or
   one or more Contact classes MUST be present.

   +--------------------+
   | DomainContacts     |
   +--------------------+
   |                    |<>--{0..1}--[ SameDomainContact ]
   |                    |<>--{1..*}--[ Contact ]
   +--------------------+

                    Figure 40: The DomainContacts Class

   The aggregate classes of the DomainContacts class are:

   SameDomainContact
      Zero or one.  STRING.  A domain name already cited in this
      document or through previous exchange that contains the identical
      contact information as the domain name in question.  The domain
      contact information associated with this domain should be used
      instead of an explicit definition with the Contact class.

   Contact
      One or more.  Contact information for the domain.  See
      Section 3.9.

   The DomainContacts class has no attributes.

3.20. Service Class

   The Service class describes a network service.  The service is
   described by a protocol, port, protocol header field, and application
   providing or using the service.

   +-------------------------+
   | Service                 |
   +-------------------------+
   | INTEGER ip-protocol     |<>--{0..1}--[ ServiceName       ]
   | ID observable-id        |<>--{0..1}--[ Port              ]
   |                         |<>--{0..1}--[ Portlist          ]
   |                         |<>--{0..1}--[ ProtoCode         ]
   |                         |<>--{0..1}--[ ProtoType         ]
   |                         |<>--{0..1}--[ ProtoField        ]
   |                         |<>--{0..1}--[ ApplicationHeader ]
   |                         |<>--{0..1}--[ EmailData         ]
   |                         |<>--{0..1}--[ Application       ]
   +-------------------------+

                       Figure 41: The Service Class

   The aggregate classes of the Service class are:

   ServiceName
      Zero or one.  A protocol name.

   Port
      Zero or one.  INTEGER.  A port number.

   Portlist
      Zero or one.  PORTLIST.  A list of port numbers.

   ProtoCode
      Zero or one.  INTEGER.  A transport-layer (Layer 4) protocol-
      specific code field (e.g., ICMP code field).

   ProtoType
      Zero or one.  INTEGER.  A transport-layer (Layer 4) protocol-
      specific type field (e.g., ICMP type field).

   ProtoField
      Zero or one.  INTEGER.  A transport-layer (Layer 4) protocol-
      specific flag field (e.g., TCP flag field).

   ApplicationHeader
      Zero or one.  A protocol header.  See Section 3.20.2.

   EmailData
      Zero or one.  Headers associated with an email message.  See
      Section 3.21.

   Application
      Zero or one.  SOFTWARE.  The application acting as either the
      client or the server for the service.

   At least one of these classes MUST be present.

   When a given System class with category="source" and another with
   category="target" are aggregated into a single Flow class, and each
   of these System classes has a Service and Portlist class, an implicit
   relationship between these Portlists exists.  If N ports are listed
   for a System@category="source", and M ports are listed for
   System@category="target", the number of ports in N must be equal to
   M.  Likewise, the ports MUST be listed in an identical sequence such
   that the n-th port in the source corresponds to the n-th port of the
   target.  If N is greater than 1, a given instance of a Flow class
   MUST only have a single instance of a System@category="source" and
   System@category="target".

   The attributes of the Service class are:

   ip-protocol
      Optional.  INTEGER.  The IANA-assigned IP protocol number per
      [IANA.Protocols].  The attribute MUST be set if a Port, Portlist,
      ProtoCode, ProtoType, or ProtoField class is present.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.20.1. ServiceName Class

   The ServiceName class identifies an application protocol.  It can be
   described by referencing an IANA-registered protocol, by referencing
   a URL, or with free-form text.

   +--------------------+
   | ServiceName        |
   +--------------------+
   |                    |<>--{0..1}--[ IANAService       ]
   |                    |<>--{0..*}--[ URL               ]
   |                    |<>--{0..*}--[ Description       ]
   +--------------------+

                     Figure 42: The ServiceName Class

   The aggregate classes of the ServiceName class are:

   IANAService
      Zero or one.  STRING.  The name of the service per the "Service
      Name" field of the registry [IANA.Ports].

   URL
      Zero or more.  URL.  A URL to a resource describing the service.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      service.

   At least one of these classes MUST be present.

   The ServiceName class has no attributes.

3.20.2. ApplicationHeader Class

   The ApplicationHeader class describes arbitrary fields from a
   protocol header and its corresponding value.

   +--------------------------+
   | ApplicationHeader        |
   +--------------------------+
   |                          |<>--{1..*}--[ ApplicationHeaderField ]
   +--------------------------+

                  Figure 43: The ApplicationHeader Class

   The aggregate class of the ApplicationHeader class is:

   ApplicationHeaderField
      One or more.  EXTENSION.  A field name and value in a protocol
      header.  The name attribute MUST be set to the field name.  The
      field value MUST be set in the element content.

   The ApplicationHeader class has no attributes.

3.21. EmailData Class

   The EmailData class describes headers from an email message and
   cryptographic hashes and signatures applied to it.

   +-------------------------+
   | EmailData               |
   +-------------------------+
   | ID observable-id        |<>--{0..*}--[ EmailTo          ]
   |                         |<>--{0..1}--[ EmailFrom        ]
   |                         |<>--{0..1}--[ EmailSubject     ]
   |                         |<>--{0..1}--[ EmailX-Mailer    ]
   |                         |<>--{0..*}--[ EmailHeaderField ]
   |                         |<>--{0..1}--[ EmailHeaders     ]
   |                         |<>--{0..1}--[ EmailBody        ]
   |                         |<>--{0..1}--[ EmailMessage     ]
   |                         |<>--{0..*}--[ HashData         ]
   |                         |<>--{0..*}--[ SignatureData    ]
   +-------------------------+

                        Figure 44: EmailData Class

   The aggregate classes of the EmailData class are:

   EmailTo
      Zero or more.  EMAIL.  The value of the "To:" header field
      (Section 3.6.3 of [RFC5322]) in an email.

   EmailFrom
      Zero or one.  EMAIL.  The value of the "From:" header field
      (Section 3.6.2 of [RFC5322]) in an email.

   EmailSubject
      Zero or one.  STRING.  The value of the "Subject:" header field in
      an email.  See Section 3.6.5 of [RFC5322].

   EmailX-Mailer
      Zero or one.  STRING.  The value of the "X-Mailer:" header field
      in an email.

   EmailHeaderField
      Zero or more.  EXTENSION.  The header name and value of an
      arbitrary header field of the email message.  The name attribute
      MUST be set to the header name.  The header value MUST be set in
      the element body.  The dtype attribute MUST be set to "string".

   EmailHeaders
      Zero or one.  STRING.  The headers of an email message.

   EmailBody
      Zero or one.  STRING.  The body of an email message.

   EmailMessage
      Zero or one.  STRING.  The headers and body of an email message.

   HashData
      Zero or more.  Hash(es) associated with this email message.  See
      Section 3.26.

   SignatureData
      Zero or more.  Signature(s) associated with this email message.
      See Section 3.27.

   The attribute of the EmailData class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.22. Record Class

   The Record class is a container class for log and audit data that
   provides supportive information about the events in an incident.  The
   source of this data will often be the output of monitoring tools.
   These logs substantiate the activity described in the document.

   +------------------------+
   | Record                 |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ RecordData ]
   | STRING ext-restriction |
   +------------------------+

                        Figure 45: The Record Class

   The aggregate classes of the Record class are:

   RecordData
      One or more.  Log or audit data generated by a particular tool.
      Separate instances of the RecordData class SHOULD be used for each
      type of log.  See Section 3.22.1.

   The attributes of the Record class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.22.1. RecordData Class

   The RecordData class describes or references log or audit data from a
   given type of tool and provides a means to annotate the output.

   +------------------------+
   | RecordData             |
   +------------------------+
   | ENUM restriction       |<>--{0..1}--[ DateTime               ]
   | STRING ext-restriction |<>--{0..*}--[ Description            ]
   | ID observable-id       |<>--{0..1}--[ Application            ]
   |                        |<>--{0..*}--[ RecordPattern          ]
   |                        |<>--{0..*}--[ RecordItem             ]
   |                        |<>--{0..*}--[ URL                    ]
   |                        |<>--{0..*}--[ FileData               ]
   |                        |<>--{0..*}--
   |                        |       [ WindowsRegistryKeysModified ]
   |                        |<>--{0..*}--[ CertificateData        ]
   |                        |<>--{0..*}--[ AdditionalData         ]
   +------------------------+

                      Figure 46: The RecordData Class

   The aggregate classes of the RecordData class are:

   DateTime
      Zero or one.  DATETIME.  A timestamp of the data found in the
      RecordItem or URL classes.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      data provided in the RecordItem or URL classes.

   Application
      Zero or one.  SOFTWARE.  Identifies the tool used to generate the
      data in the RecordItem or URL classes.

   RecordPattern
      Zero or more.  A search string to precisely find the relevant data
      in the RecordItem or URL classes.  See Section 3.22.2.

   RecordItem
      Zero or more.  EXTENSION.  Log, audit, or forensic data to support
      the conclusions made during the course of analyzing the incident.

   URL
      Zero or more.  URL.  A URL reference to a log or audit data.

   FileData
      Zero or one.  The files involved in the incident.  See
      Section 3.25.

   WindowsRegistryKeysModified
      Zero or more.  The registry keys that were involved in the
      incident.  See Section 3.23.

   CertificateData
      Zero or more.  The certificates that were involved in the
      incident.  See Section 3.24.

   AdditionalData
      Zero or more.  EXTENSION.  An extension mechanism for data not
      explicitly represented in the data model.

   At least one of the following classes MUST be present: RecordItem,
   URL, FileData, WindowsRegistryKeysModified, CertificateData, or
   AdditionalData.

   The attributes of the RecordData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.22.2. RecordPattern Class

   The RecordPattern class describes where in the log data provided or
   referenced in the RecordData class relevant information can be found.
   It provides a way to reference subsets of information, identified by
   a pattern, in a large log file, audit trail, or forensic data.

   +-----------------------+
   | RecordPattern         |
   +-----------------------+
   | STRING                |
   |                       |
   | ENUM type             |
   | STRING ext-type       |
   | INTEGER offset        |
   | ENUM offsetunit       |
   | STRING ext-offsetunit |
   | INTEGER instance      |
   +-----------------------+

                    Figure 47: The RecordPattern Class

   The content of the class is of type STRING and specifies a search
   pattern.

   The attributes of the RecordPattern class are:

   type
      Required.  ENUM.  Describes the type of pattern being specified in
      the element content.  The default is "regex".  These values are
      maintained in the "RecordPattern-type" IANA registry per
      Section 10.2.

      1.  regex.  Regular expression as defined by POSIX Extended
          Regular Expressions (ERE) in Chapter 9 of [IEEE.POSIX].

      2.  binary.  Binhex-encoded binary pattern, per the HEXBIN data
          type.

      3.  xpath.  XML Path (XPath) [W3C.XPATH].

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   offset
      Optional.  INTEGER.  Amount of units (determined by the offsetunit
      attribute) to seek into the RecordItem data before matching the
      pattern.

   offsetunit
      Optional.  ENUM.  Describes the units of the offset attribute.
      The default is "line".  These values are maintained in the
      "RecordPattern-offsetunit" IANA registry per Section 10.2.

      1.  line.  Offset is a count of lines.

      2.  byte.  Offset is a count of bytes.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-offsetunit
      Optional.  STRING.  A means by which to extend the offsetunit
      attribute.  See Section 5.1.1.

   instance
      Optional.  INTEGER.  Number of times to apply the specified
      pattern.

3.23. WindowsRegistryKeysModified Class

   The WindowsRegistryKeysModified class describes Windows operating
   system registry keys and the operations that were performed on them.
   This class was derived from [RFC5901].

   +-----------------------------+
   | WindowsRegistryKeysModified |
   +-----------------------------+
   | ID observable-id            |<>--{1..*}--[ Key ]
   +-----------------------------+

             Figure 48: The WindowsRegistryKeysModified Class

   The aggregate classes of the WindowsRegistryKeysModified class are:

   Key
      One or more.  The Windows registry key.  See Section 3.23.1.

   The attribute of the WindowsRegistryKeysModified class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.23.1. Key Class

   The Key class describes a Windows operating system registry key name
   and value pair, as well as the operation performed on it.

   +---------------------------+
   | Key                       |
   +---------------------------+
   | ENUM registryaction       |<>----------[ KeyName  ]
   | STRING ext-registryaction |<>--{0..1}--[ KeyValue ]
   | ID observable-id          |
   +---------------------------+

                         Figure 49: The Key Class

   The aggregate classes of the Key class are:

   KeyName
      One.  STRING.  The name of a Windows operating system registry key
      (e.g., [HKEY_LOCAL_MACHINE\Software\Test\KeyName]).

   KeyValue
      Zero or one.  STRING.  The value of the registry key identified in
      the KeyName class encoded per the .reg file format [KB310516].

   The attributes of the Key class are:

   registryaction
      Optional.  ENUM.  The type of action taken on the registry key.
      These values are maintained in the "Key-registryaction" IANA
      registry per Section 10.2.

      1.  add-key.  Registry key added.

      2.  add-value.  Value added to a registry key.

      3.  delete-key.  Registry key deleted.

      4.  delete-value.  Value deleted from a registry key.

      5.  modify-key.  Registry key modified.

      6.  modify-value.  Value modified in a registry key.

      7.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-registryaction
      Optional.  STRING.  A means by which to extend the registryaction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.24. CertificateData Class

   The CertificateData class describes X.509 certificates.

   +------------------------+
   | CertificateData        |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ Certificate    ]
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                   Figure 50: The CertificateData Class

   The aggregate classes of the CertificateData class are:

   Certificate
      One or more.  A description of an X.509 certificate or certificate
      chain.  See Section 3.24.1.

   The attributes of the CertificateData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.24.1. Certificate Class

   The Certificate class describes a given X.509 certificate or
   certificate chain.

   +--------------------------+
   | Certificate              |
   +--------------------------+
   | ID observable-id         |<>----------[ ds:X509Data    ]
   |                          |<>--{0..*}--[ Description    ]
   +--------------------------+

                     Figure 51: The Certificate Class

   The aggregate classes of the Certificate class are:

   ds:X509Data
      One.  A given X.509 certificate or chain.  See Section 4.4.4 of
      [W3C.XMLSIG].

   Description
      Zero or more.  ML_STRING.  A free-form text description explaining
      the context of this certificate.

   The attributes of the Certificate class are:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.25. FileData Class

   The FileData class describes a file or set of files.

   +------------------------+
   | FileData               |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ File      ]
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                       Figure 52: The FileData Class

   The aggregate classes of the FileData class are:

   File
      One or more.  A description of a file.  See Section 3.25.1.

   The attributes of the FileData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.25.1. File Class

   The File class describes a file; its associated metadata; and
   cryptographic hashes and signatures applied to it.

   +-----------------------+
   | File                  |
   +-----------------------+
   | ID observable-id      |<>--{0..1}--[ FileName           ]
   |                       |<>--{0..1}--[ FileSize           ]
   |                       |<>--{0..1}--[ FileType           ]
   |                       |<>--{0..*}--[ URL                ]
   |                       |<>--{0..1}--[ HashData           ]
   |                       |<>--{0..1}--[ SignatureData      ]
   |                       |<>--{0..1}--[ AssociatedSoftware ]
   |                       |<>--{0..*}--[ FileProperties     ]
   +-----------------------+

                         Figure 53: The File Class

   The aggregate classes of the File class are:

   FileName
      Zero or one.  STRING.  The name of the file.

   FileSize
      Zero or one.  INTEGER.  The size of the file in bytes.

   FileType
      Zero or one.  STRING.  The type of file per the IANA "Media Types"
      registry [IANA.Media].  Valid values correspond to the text in the
      "Template" column (e.g., "application/pdf").

   URL
      Zero or more.  URL.  A URL reference to the file.

   HashData
      Zero or one.  Hash(es) associated with this file.  See
      Section 3.26.

   SignatureData
      Zero or one.  Signature(s) associated with this file.  See
      Section 3.27.

   AssociatedSoftware
      Zero or one.  SOFTWARE.  The software application or operating
      system to which this file belongs or by which it can be processed.

   FileProperties
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model to describe properties of the file.

   The attributes of the File class are:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.26. HashData Class

   The HashData class describes different types of hashes on a given
   object (e.g., file, part of a file, email).

   +--------------------------+
   | HashData                 |
   +--------------------------+
   | ENUM scope               |<>--{0..1}--[ HashTargetID ]
   |                          |<>--{0..*}--[ Hash         ]
   |                          |<>--{0..*}--[ FuzzyHash    ]
   +--------------------------+

                       Figure 54: The HashData Class

   The aggregate classes of the HashData class are:

   HashTargetID
      Zero or one.  STRING.  An identifier that references a subset of
      the object being hashed.  The semantics of this identifier are
      specified by the scope attribute.

   Hash
      Zero or more.  The hash of an object.  See Section 3.26.1.

   FuzzyHash
      Zero or more.  The fuzzy hash of an object.  See Section 3.26.2.

   At least one instance of either Hash or FuzzyHash MUST be present.

   The attribute of the HashData class is:

   scope
      Required.  ENUM.  Describes on which part of the object the hash
      should be applied.  These values are maintained in the "HashData-
      scope" IANA registry per Section 10.2.

      1.  file-contents.  A hash computed over the entire contents of a
          file.

      2.  file-pe-section.  A hash computed on a given section of a
          Windows Portable Executable (PE) file.  If set to this value,
          the HashTargetID class MUST identify the section being hashed.
          A section is identified by an ordinal number (starting at 1)
          corresponding to the order in which the given section header
          was defined in the Section Table of the PE file header.

      3.  file-pe-iat.  A hash computed on the Import Address
          Table (IAT) of a PE file.  As IAT hashes are often tool
          dependent, if this value is set, the Application class of
          either the Hash or FuzzyHash classes MUST specify the tool
          used to generate the hash.

      4.  file-pe-resource.  A hash computed on a given resource in a PE
          file.  If set to this value, the HashTargetID class MUST
          identify the resource being hashed.  A resource is identified
          by an ordinal number (starting at 1) corresponding to the
          order in which the given resource is declared in the Resource
          Directory of the Data Dictionary in the PE file header.

      5.  file-pdf-object.  A hash computed on a given object in a
          Portable Document Format (PDF) file.  If set to this value,
          the HashTargetID class MUST identify the object being hashed.
          This object is identified by its offset in the PDF file.

      6.  email-hash.  A hash computed over the headers and body of an
          email message.

      7.  email-headers-hash.  A hash computed over all of the headers
          of an email message.

      8.  email-body-hash.  A hash computed over the body of an email
          message.

      9.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-scope
      Optional.  STRING.  A means by which to extend the scope
      attribute.  See Section 5.1.1.

3.26.1. Hash Class

   The Hash class describes a cryptographic hash value; the algorithm
   and application used to generate it; and the canonicalization method
   applied to the object being hashed.

   +----------------+
   | Hash           |
   +----------------+
   |                |<>----------[ ds:DigestMethod            ]
   |                |<>----------[ ds:DigestValue             ]
   |                |<>--{0..1}--[ ds:CanonicalizationMethod  ]
   |                |<>--{0..1}--[ Application                ]
   +----------------+

                         Figure 55: The Hash Class

   The aggregate classes of the Hash class are:

   ds:DigestMethod
      One.  The hash algorithm used to generate the hash.  See
      Section 4.3.3.5 of [W3C.XMLSIG].

   ds:DigestValue
      One.  The computed hash value.  See Section 4.3.3.6 of
      [W3C.XMLSIG].

   ds:CanonicalizationMethod
      Zero or one.  The canonicalization method used on the object being
      hashed.  See Section 4.3.1 of [W3C.XMLSIG].

   Application
      Zero or one.  SOFTWARE.  The application used to calculate the
      hash.

   The HashData class has no attributes.

3.26.2. FuzzyHash Class

   The FuzzyHash class describes a fuzzy hash and the application used
   to generate it.

   +--------------------------+
   | FuzzyHash                |
   +--------------------------+
   |                          |<>--{1..*}--[ FuzzyHashValue ]
   |                          |<>--{0..1}--[ Application    ]
   |                          |<>--{0..*}--[ AdditionalData ]
   +--------------------------+

                      Figure 56: The FuzzyHash Class

   The aggregate classes of the FuzzyHash class are:

   FuzzyHashValue
      One or more.  EXTENSION.  The computed fuzzy hash value.

   Application
      Zero or one.  SOFTWARE.  The application used to calculate the
      hash.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The FuzzyData class has no attributes.

3.27. SignatureData Class

   The SignatureData class describes different types of digital
   signatures on an object.

   +--------------------------+
   | SignatureData            |
   +--------------------------+
   |                          |<>--{1..*}--[ ds:Signature ]
   +--------------------------+

                    Figure 57: The SignatureData Class

   The aggregate class of the SignatureData class is:

   Signature
      One or more.  A given signature.  See Section 4.2 of [W3C.XMLSIG].

   The SignatureData class has no attributes.

3.28. IndicatorData Class

   The IndicatorData class describes indicators and metadata associated
   with them.

   +--------------------------+
   | IndicatorData            |
   +--------------------------+
   |                          |<>--{1..*}--[ Indicator      ]
   +--------------------------+

                    Figure 58: The IndicatorData Class

   The aggregate class of the IndicatorData class is:

   Indicator
      One or more.  A description of an indicator.  See Section 3.29.

   The IndicatorData class has no attributes.

3.29. Indicator Class

   The Indicator class describes an indicator.  An indicator consists of
   observable features and phenomenon that aid in the forensic or
   proactive detection of malicious activity and associated metadata.
   An indicator can be described outright by referencing or composing
   previously defined indicators or by referencing observables described
   in the incident report found in this document.

   +------------------------+
   | Indicator              |
   +------------------------+
   | ENUM restriction       |<>----------[ IndicatorID            ]
   | STRING ext-restriction |<>--{0..*}--[ AlternativeIndicatorID ]
   |                        |<>--{0..*}--[ Description            ]
   |                        |<>--{0..1}--[ StartTime              ]
   |                        |<>--{0..1}--[ EndTime                ]
   |                        |<>--{0..1}--[ Confidence             ]
   |                        |<>--{0..*}--[ Contact                ]
   |                        |<>--{0..1}--[ Observable             ]
   |                        |<>--{0..1}--[ ObservableReference    ]
   |                        |<>--{0..1}--[ IndicatorExpression    ]
   |                        |<>--{0..1}--[ IndicatorReference     ]
   |                        |<>--{0..*}--[ NodeRole               ]
   |                        |<>--{0..*}--[ AttackPhase            ]
   |                        |<>--{0..*}--[ Reference              ]
   |                        |<>--{0..*}--[ AdditionalData         ]
   +------------------------+

                      Figure 59: The Indicator Class

   The aggregate classes of the Indicator class are:

   IndicatorID
      One.  An identifier for this indicator.  See Section 3.29.1.

   AlternativeIndicatorID
      Zero or more.  An alternative identifier for this indicator.  See
      Section 3.29.2.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      indicator.

   StartTime
      Zero or one.  DATETIME.  A timestamp of the start of the time
      period during which this indicator is valid.

   EndTime
      Zero or one.  DATETIME.  A timestamp of the end of the time period
      during which this indicator is valid.

   Confidence
      Zero or one.  An estimate of the confidence in the quality of the
      indicator.  See Section 3.12.5.

   Contact
      Zero or more.  Contact information for this indicator.  See
      Section 3.9.

   Observable
      Zero or one.  An observable feature or phenomenon of this
      indicator.  See Section 3.29.3.

   ObservableReference
      Zero or one.  A reference to an observable feature or phenomenon
      defined elsewhere in the document.  See Section 3.29.6.

   IndicatorExpression
      Zero or one.  A composition of observables.  See Section 3.29.4.

   IndicatorReference
      Zero or one.  A reference to an indicator.  See Section 3.29.7.

   NodeRole
      Zero or more.  The role of the system in the attack should this
      indicator be matched to it.  See Section 3.18.2.

   AttackPhase
      Zero or more.  The phase in an attack life cycle during which this
      indicator might be seen.  See Section 3.29.8.

   Reference
      Zero or more.  A reference to additional information relevant to
      this indicator.  See Section 3.11.1.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The Indicator class MUST have exactly one instance of an Observable,
   IndicatorExpression, ObservableReference, or IndicatorReference
   class.

   The StartTime and EndTime classes can be used to define an interval
   during which the indicator is valid.  If both classes are present,
   the indicator is consider valid only during the described interval.
   If neither class is provided, the indicator is considered valid
   during any time interval.  If only a StartTime is provided, the
   indicator is valid anytime after this timestamp.  If only an EndTime
   is provided, the indicator is valid anytime prior to this timestamp.

   The attributes of the Indicator class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.29.1. IndicatorID Class

   The IndicatorID class identifies an indicator with a globally unique
   identifier.  The combination of the name and version attributes and
   the element content form this identifier.  Indicators generated by
   given CSIRT MUST NOT reuse the same value unless they are referencing
   the same indicator.

   +------------------+
   | IndicatorID      |
   +------------------+
   | ID               |
   |                  |
   | STRING name      |
   | STRING version   |
   +------------------+

                     Figure 60: The IndicatorID Class

   The content of the class is of type ID and specifies an identifier
   for an indicator.

   The attributes of the IndicatorID class are:

   name
      Required.  STRING.  An identifier describing the CSIRT that
      created the indicator.  In order to have a globally unique CSIRT
      name, the fully qualified domain name associated with the CSIRT
      MUST be used.  This format is identical to the IncidentID@name
      attribute in Section 3.4.

   version
      Required.  STRING.  A version number of an indicator.

3.29.2. AlternativeIndicatorID Class

   The AlternativeIndicatorID class lists alternative identifiers for an
   indicator.

   +-------------------------+
   | AlternativeIndicatorID  |
   +-------------------------+
   | ENUM restriction        |<>--{1..*}--[ IndicatorReference ]
   | STRING ext-restriction  |
   +-------------------------+

                Figure 61: The AlternativeIndicatorID Class

   The aggregate class of the AlternativeIndicatorID class is:

   IndicatorReference
      One or more.  A reference to an indicator.  See Section 3.29.7.

   The attributes of the AlternativeIndicatorID class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.29.3. Observable Class

   The Observable class describes a feature and phenomenon that can be
   observed or measured for the purposes of detecting malicious
   behavior.

   +------------------------+
   | Observable             |
   +------------------------+
   | ENUM restriction       |<>--{0..1}--[ System                      ]
   | STRING ext-restriction |<>--{0..1}--[ Address                     ]
   |                        |<>--{0..1}--[ DomainData                  ]
   |                        |<>--{0..1}--[ Service                     ]
   |                        |<>--{0..1}--[ EmailData                   ]
   |                        |<>--{0..1}--[ WindowsRegistryKeysModified ]
   |                        |<>--{0..1}--[ FileData                    ]
   |                        |<>--{0..1}--[ CertificateData             ]
   |                        |<>--{0..1]--[ RegistryHandle              ]
   |                        |<>--{0..1}--[ RecordData                  ]
   |                        |<>--{0..1}--[ EventData                   ]
   |                        |<>--{0..1}--[ Incident                    ]
   |                        |<>--{0..1}--[ Expectation                 ]
   |                        |<>--{0..1}--[ Reference                   ]
   |                        |<>--{0..1}--[ Assessment                  ]
   |                        |<>--{0..1}--[ DetectionPattern            ]
   |                        |<>--{0..1}--[ HistoryItem                 ]
   |                        |<>--{0..1}--[ BulkObservable              ]
   |                        |<>--{0..*}--[ AdditionalData              ]
   +------------------------+

                      Figure 62: The Observable Class

   The aggregate classes of the Observable class are:

   System
      Zero or one.  A System observable.  See Section 3.17.

   Address
      Zero or one.  An Address observable.  See Section 3.18.1.

   DomainData
      Zero or one.  A DomainData observable.  See Section 3.19.

   Service
      Zero or one.  A Service observable.  See Section 3.20.

   EmailData
      Zero or one.  An EmailData observable.  See Section 3.21.

   WindowsRegistryKeysModified
      Zero or one.  A WindowsRegistryKeysModified observable.  See
      Section 3.23.

   FileData
      Zero or one.  A FileData observable.  See Section 3.25.

   CertificateData
      Zero or one.  A CertificateData observable.  See Section 3.24.

   RegistryHandle
      Zero or one.  A RegistryHandle observable.  See Section 3.9.1.

   RecordData
      Zero or one.  A RecordData observable.  See Section 3.22.1.

   EventData
      Zero or one.  An EventData observable.  See Section 3.14.

   Incident
      Zero or one.  An Incident observable.  See Section 3.2.

   Expectation
      Zero or one.  An Expectation observable.  See Section 3.15.

   Reference
      Zero or one.  A Reference observable.  See Section 3.11.1.

   Assessment
      Zero or one.  An Assessment observable.  See Section 3.12.

   DetectionPattern
      Zero or one.  A DetectionPattern observable.  See Section 3.10.1.

   HistoryItem
      Zero or one.  A HistoryItem observable.  See Section 3.13.1.

   BulkObservable
      Zero or one.  A bulk list of observables.  See Section 3.29.3.1.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The Observable class MUST have exactly one of the possible child
   classes.

   The attributes of the Observable class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.29.3.1. BulkObservable Class

   The BulkObservable class allows the enumeration of a single type of
   observable without requiring each one to be encoded individually in
   multiple instances of the same class.

   The type attribute describes the type of observable listed in the
   child BulkObservableList class.  The BulkObservableFormat class
   optionally provides additional metadata.

   +---------------------------+
   | BulkObservable            |
   +---------------------------+
   | ENUM type                 |<>--{0..1}--[ BulkObservableFormat ]
   | STRING ext-type           |<>----------[ BulkObservableList   ]
   |                           |<>--{0..*}--[ AdditionalData       ]
   +---------------------------+

                    Figure 63: The BulkObservable Class

   The aggregate classes of the BulkObservable class are:

   BulkObservableFormat
      Zero or one.  Provides additional metadata about the observables
      enumerated in the BulkObservableList class.  See
      Section 3.29.3.1.1.

   BulkObservableList
      One.  STRING.  A list of observables, one per line.  Each line is
      separated with either a LF character or CR and LF characters.  The
      type attribute specifies which observables will be listed.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the BulkObservable class are:

   type
      Optional.  ENUM.  The type of the observable listed in the child
      ObservableList class.  These values are maintained in the
      "BulkObservable-type" IANA registry per Section 10.2.

      1.   asn.  Autonomous System Number (per the Address@category
           attribute).

      2.   atm.  Asynchronous Transfer Mode (ATM) address (per the
           Address@category attribute).

      3.   e-mail.  Email address (per the Address@category attribute).

      4.   ipv4-addr.  IPv4 host address in dotted-decimal notation,
           e.g., 192.0.2.1 (per the Address@category attribute).

      5.   ipv4-net.  IPv4 network address in dotted-decimal notation,
           slash, significant bits, e.g., 192.0.2.0/24 (per the
           Address@category attribute).

      6.   ipv4-net-mask.  IPv4 network address in dotted-decimal
           notation, slash, network mask in dotted-decimal notation,
           i.e., 192.0.2.0/255.255.255.0 (per the Address@category
           attribute).

      7.   ipv6-addr.  IPv6 host address, e.g., 2001:DB8::3 (per the
           Address@category attribute).

      8.   ipv6-net.  IPv6 network address, slash, significant bits,
           e.g., 2001:DB8::/32 (per the Address@category attribute).

      9.   ipv6-net-mask.  IPv6 network address, slash, network mask
           (per the Address@category attribute).

      10.  mac.  Media Access Control (MAC) address, i.e., a:b:c:d:e:f
           (per the Address@category attribute).

      11.  site-uri.  A URL or URI for a resource (per the
           Address@category attribute).

      12.  domain-name.  A fully qualified domain name or part of a name
           (e.g., fqdn.example.com, example.com).

      13.  domain-to-ipv4.  A mapping of FQDN to IPv4 address specified
           as a comma-separated list (e.g., "fqdn.example.com,
           192.0.2.1").

      14.  domain-to-ipv6.  A mapping of FQDN to IPv6 address specified
           as a comma-separated list (e.g., "fqdn.example.com,
           2001:DB8::3").

      15.  domain-to-ipv4-timestamp.  Same as domain-to-ipv4 but with a
           timestamp (in the DATETIME format) of the resolution (e.g.,
           "fqdn.example.com, 192.0.2.1, 2015-06-11T00:38:31-06:00").

      16.  domain-to-ipv6-timestamp.  Same as domain-to-ipv6 but with a
           timestamp (in the DATETIME format) of the resolution (e.g.,
           "fqdn.example.com, 2001:DB8::3, 2015-06-11T00:38:31-06:00").

      17.  ipv4-port.  An IPv4 address, port, and protocol tuple (e.g.,
           192.0.2.1, 80, TCP).  The protocol name corresponds to the
           "Keyword" column in the "Assigned Internet Protocol Numbers"
           registry [IANA.Protocols].

      18.  ipv6-port.  An IPv6 address, port, and protocol tuple (e.g.,
           2001:DB8::3, 80, TCP).  The protocol name corresponds to the
           "Keyword" column in the "Assigned Internet Protocol Numbers"
           registry [IANA.Protocols].

      19.  windows-reg-key.  A Microsoft Windows registry key.

      20.  file-hash.  A file hash.  The format of this hash is
           described in the Hash class that MUST be present in a sibling
           BulkObservableFormat class.

      21.  email-x-mailer.  An X-Mailer field from an email.

      22.  email-subject.  An email subject line.

      23.  http-user-agent.  A User Agent field from an HTTP request
           header (e.g., "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0)
           Gecko/20100101 Firefox/38.0").

      24.  http-request-uri.  The Request URI from an HTTP request
           header.

      25.  mutex.  The name of a system mutex (mutual exclusion lock).

      26.  file-path.  A file path (e.g., "/tmp/local/file",
           "c:\windows\system32\file.sys").

      27.  user-name.  A username.

      28.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.29.3.1.1. BulkObservableFormat Class

   The ObservableFormat class specifies metadata about the format of an
   observable enumerated in a sibling BulkObservableList class.

   +---------------------------+
   | BulkObservableFormat      |
   +---------------------------+
   |                           |<>--{0..1}--[ Hash             ]
   |                           |<>--{0..*}--[ AdditionalData   ]
   +---------------------------+

                 Figure 64: The BulkObservableFormat Class

   The aggregate classes of the BulkObservableFormat class are:

   Hash
      Zero or one.  Describes the format of a hash.  See Section 3.26.1.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The BulkObservableFormat class has no attributes.

   Either Hash or AdditionalData MUST be present.

3.29.4. IndicatorExpression Class

   The IndicatorExpression describes an expression composed of observed
   phenomenon, features, or indicators.  Elements of the expression can
   be described directly, reference relevant data from other parts of a
   given IODEF document, or reference previously defined indicators.

   All child classes of a given instance of IndicatorExpression form a
   boolean algebraic expression where the operator between them is
   determined by the operator attribute.

   +--------------------------+
   | IndicatorExpression      |
   +--------------------------+
   | ENUM operator            |<>--{0..*}--[ IndicatorExpression  ]
   | STRING ext-operator      |<>--{0..*}--[ Observable           ]
   |                          |<>--{0..*}--[ ObservableReference  ]
   |                          |<>--{0..*}--[ IndicatorReference   ]
   |                          |<>--{0..1}--[ Confidence           ]
   |                          |<>--{0..*}--[ AdditionalData       ]
   +--------------------------+

                 Figure 65: The IndicatorExpression Class

   The aggregate classes of the IndicatorExpression class are:

   IndicatorExpression
      Zero or more.  An expression composed of other observables or
      indicators.  See Section 3.29.4.

   Observable
      Zero or more.  A description of an observable.  See
      Section 3.29.3.

   ObservableReference
      Zero or more.  A reference to an observable.  See Section 3.29.6.

   IndicatorReference
      Zero or more.  A reference to an indicator.  See Section 3.29.7.

   Confidence
      Zero or one.  An estimate of the confidence in the quality of the
      terms expressed in the expression.  See Section 3.12.5.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the IndicatorExpression class are:

   operator
      Optional.  ENUM.  The operator to be applied between the child
      elements.  See Section 3.29.5 for parsing guidance.  The default
      value is "and".  These values are maintained in the
      "IndicatorExpression-operator" IANA registry per Section 10.2.

      1.  not.  negation operator.

      2.  and.  conjunction operator.

      3.  or.  disjunction operator.

      4.  xor.  exclusive disjunction operator.

   ext-operator
      Optional.  STRING.  A means by which to extend the operator
      attribute.  See Section 5.1.1.

3.29.5. Expressions with IndicatorExpression

   Boolean algebraic expressions can be used to specify relationships
   between observables and indicators.  These expressions are
   constructed through the use of the operator attribute and parent-
   child relationships in IndicatorExpressions.  These expressions
   should be parsed as follows:

   1.  The operator specified by the operator attribute is applied
       between each of the child elements of the immediate parent
       IndicatorExpression element.  If no operator attribute is
       specified, it should be assumed to be the conjunction operator
       (i.e., operator="and").

   2.  A nested IndicatorExpression element with a parent
       IndicatorExpression is the equivalent of a parentheses in the
       expression.

   The following examples in Figures 66 through 70 illustrate these
   parsing rules:

   1     : <IndicatorExpression>
   2 [O1]:    <Observable>..</Observable>
   3 [O2]:    <Observable>..</Observable>
   4     : </IndicatorExpression>

   Equivalent expression: (O1 AND O2)

      Figure 66: Nested Elements in an IndicatorExpression without an
                       Operator Attribute Specified

   1     : <IndicatorExpression operator="or">
   2 [O1]:    <Observable>..</Observable>
   3 [O2]:    <Observable>..</Observable>
   4     : </IndicatorExpression>

   Equivalent expression: (O1 OR O2)

   Figure 67: Nested Elements in an IndicatorExpression with an Operator
                            Attribute Specified

   1     : <IndicatorExpression operator="or">
   2     :    <IndicatorExpression operator="or">
   3 [O1]:      <Observable>..</Observable>
   4 [O2]:      <Observable>..</Observable>
   5     :    </IndicatorExpression>
   6 [O3]:    <Observable>..</Observable>
   7     : </IndicatorExpression>

   Equivalent expression: ((O1 OR O2) OR O3)

   Figure 68: Nested Elements with a Recursive IndicatorExpression with
                      an Operator Attribute Specified

   1     : <IndicatorExpression operator="not">
   2     :    <IndicatorExpression operator="and">
   3 [O1]:      <Observable>..</Observable>
   4 [O2]:      <Observable>..</Observable>
   5     :    </IndicatorExpression>
   6     : </IndicatorExpression>

   Equivalent expression: (NOT (O1 AND O2))

   Figure 69: A Recursive IndicatorExpression with an Operator Attribute
                                 Specified

    1                          :    <IndicatorExpression operator="or">
    2                          :      <IndicatorExpression>
    3 [O1 with low confidence] :        <Observable>..</Observable>
    4                          :        <Confidence rating="low" />
    5                          :      </IndicatorExpression>
    6                          :      <IndicatorExpression>
    7 [O2 with high confidence]:        <Observable>..</Observable>
    8                          :        <Confidence rating="high" />
    9                          :      </IndicatorExpression>
   10                          :    </IndicatorExpression>

   Equivalent expression: ((O1) OR (O2))

          Figure 70: Varying Confidence on Particular Observables

   Invalid algebraic expressions while valid XML MUST NOT be specified.

3.29.6. ObservableReference Class

   The ObservableReference describes a reference to an observable
   feature or phenomenon described elsewhere in the document.

   The ObservableReference class has no content.

   +-------------------------+
   | ObservableReference     |
   +-------------------------+
   | IDREF uid-ref           |
   +-------------------------+

                 Figure 71: The ObservableReference Class

   The ObservableReference class has no content.

   The attribute of the ObservableReference class is:

   uid-ref
      Required.  IDREF.  An identifier that serves as a reference to a
      class in the IODEF document.  The referenced class will have this
      identifier set in its observable-id attribute.

3.29.7. IndicatorReference Class

   The IndicatorReference describes a reference to an indicator.  This
   reference may be to an indicator described in this IODEF document or
   in a previously exchanged IODEF document.

   The IndicatorReference class has no content.

   +--------------------------+
   | IndicatorReference       |
   +--------------------------+
   | IDREF uid-ref            |
   | STRING euid-ref          |
   | STRING version           |
   +--------------------------+

                  Figure 72: The IndicatorReference Class

   The attributes of the IndicatorReference class are:

   uid-ref
      Optional.  IDREF.  An identifier that references an Indicator
      class in the IODEF document.  The referenced Indicator class will
      have this identifier set in its IndicatorID class.

   euid-ref
      Optional.  STRING.  An identifier that references an IndicatorID
      not in this IODEF document.

   version
      Optional.  STRING.  A version number of an indicator.

   Either the uid-ref or the euid-ref attribute MUST be set.

3.29.8. AttackPhase Class

   The AttackPhase class describes a particular phase of an attack life
   cycle.

   +------------------------+
   | AttackPhase            |
   +------------------------+
   |                        |<>--{0..*}--[ AttackPhaseID  ]
   |                        |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                     Figure 73: The AttackPhase Class

   The aggregate classes of the AttackPhase class are:

   AttackPhaseID
      Zero or more.  STRING.  An identifier for the phase of the attack.

   URL
      Zero or more.  URL.  A URL to a resource describing this phase of
      the attack.

   Description
      Zero or more.  ML_STRING.  A free-form text description of this
      phase of the attack.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   AttackPhase MUST have at least one instance of a child class.

   The AttackPhase class has no attributes.

4.  Processing Considerations

   This section provides additional requirements and guidance on
   creating and processing IODEF documents.

4.1. Encoding

   Every IODEF document MUST begin with an XML declaration and MUST
   specify the XML version used.  The character encoding MUST also be
   explicitly specified.  UTF-8 [RFC3629] SHOULD be used unless UTF-16
   [RFC2781] is necessary.  Encodings other than UTF-8 and UTF-16 SHOULD
   NOT be used.  The IODEF conforms to all XML data-encoding conventions
   and constraints.

   The XML declaration with UTF-8 character encoding will read as
   follows:

   <?xml version="1.0" encoding="UTF-8" ?>

   Certain characters have special meaning in XML and MUST not appear in
   literal form.  Per Section 2.4 of [W3C.XML], these characters MUST be
   escaped with a numeric character or entity reference.

4.2. IODEF Namespace

   The IODEF schema declares a namespace of
   "urn:ietf:params:xml:ns:iodef-2.0" and registers it per [W3C.XMLNS].
   Each IODEF document MUST include a valid reference to the IODEF
   schema using the "xsi:schemaLocation" attribute.  An example of such
   a declaration would look as follows:

   <IODEF-Document
      version="2.00" lang="en-US"
      xmlns:iodef="urn:ietf:params:xml:ns:iodef-2.0"
      xsi:schemaLocation="urn:ietf:params:xmls:schema:iodef-2.0" ...>

4.3. Validation

   IODEF documents MUST be well-formed XML.  It is RECOMMENDED that
   recipients validate the document against the schema described in
   Section 8.  However, mere conformance to this schema is not
   sufficient for a semantically valid IODEF document.  The text of
   Section 3 describes further formatting and constraints, including
   some that cannot be conveniently encoded in the schema.  These MUST
   also be considered by an IODEF implementation.  Furthermore, the
   enumerated values present in this document are a static list that
   will be incomplete over time as select attributes can be extended by
   a corresponding IANA registry per Section 10.2.  Therefore, IODEF

   implementations SHOULD periodically update their schema and MAY need
   to update their parsing algorithms to incorporate newly registered
   values.

4.4. Incompatibilities with v1

   The IODEF data model in this document makes a number of changes to
   [RFC5070].  These changes were largely additive -- classes and
   enumerated values were added.  However, some incompatibilities
   between [RFC5070] and this new specification were introduced.  These
   incompatibilities are as follows:

   o  The IODEF-Document@version attribute is set to "2.0".

   o  Attributes with enumerated values can now also be extended with
      IANA registries.

   o  All iodef:MLStringType classes use xml:lang.  IODEF-Document also
      uses xml:lang.

   o  The Service@ip_protocol attribute was renamed to @ip-protocol.

   o  The Node/NodeName class was removed in favor of representing
      domain names with Node/DomainData/Name class.  The Node/DataTime
      class was also removed, so that the Node/DomainData/
      DateDomainWasChecked class can represent the time at which the
      name-to-address resolution occurred.

   o  The Node/NodeRole class was moved to System/NodeRole.

   o  The Reference class is now defined by [RFC7495].

   o  The data previously represented in the Impact class is now in the
      SystemImpact and IncidentCategory classes.  The Impact class has
      been removed.

   o  The semantics of Counter@type are now represented in Counter@unit.

   o  The IODEF-Document@formatid attribute has been renamed to @format-
      id.

   o  The Incident/ReportTime class is no longer required.  However, the
      GenerationTime class is required.

   o  The Fax class was removed and is now represented by a generic
      Telephone class.

   o  The Telephone, Email, and PostalAddress classes were redefined
      from improved internationalization.

   o  The "ipv6-net-mask" value was removed from the category attribute
      of Address.

5.  Extending the IODEF

   In order to support the dynamic nature of security operations, the
   IODEF data model will need to continue to evolve.  This section
   discusses how new data elements can be incorporated into the IODEF.
   There is support to add additional enumerated values and new classes.
   Adding additional attributes to existing classes is not supported.

   These extension mechanisms are designed so that adding new data
   elements is possible without requiring modifications to this
   document.  Extensions can be implemented publicly or privately.  With
   proven value, well-documented extensions can be incorporated into
   future versions of the specification.

5.1. Extending the Enumerated Values of Attributes

   Additional enumerated values can be added to select attributes either
   through the use of specially marked attributes with the "ext-" prefix
   or through a set of corresponding IANA registries.  The former
   approach allows for the extension to remain private.  The latter
   approach is public.

5.1.1. Private Extension of Enumerated Values

   The data model supports adding new enumerated values to an attribute
   without public registration.  For each attribute that supports this
   extension technique, there is a corresponding attribute in the same
   element whose name is identical but with a prefix of "ext-".  This
   special attribute is referred to as the extension attribute.  The
   attribute being extended is referred to as an extensible attribute.
   For example, an extensible attribute named "foo" will have a
   corresponding extension attribute named "ext-foo".  An element may
   have many extensible attributes.

   In addition to a corresponding extension attribute, each extensible
   attribute has "ext-value" as one its possible enumerated values.
   Selection of this particular value in an extensible attribute signals
   that the extension attribute contains data.  Otherwise, this
   "ext-value" value has no meaning.

   In order to add a new enumerated value to an extensible attribute,
   the value of this attribute MUST be set to "ext-value", and the new
   desired value MUST be set in the corresponding extension attribute.
   For example, extending the type attribute of the SystemImpact class
   would look as follows:

    <SystemImpact type="ext-value" ext-type="new-attack-type">

   A given extension attribute MUST NOT be set unless the corresponding
   extensible attribute has been set to "ext-value".

5.1.2. Public Extension of Enumerated Values

   The data model also supports publicly extending select enumerated
   attributes.  A new entry can be added by registering a new entry in
   the appropriate IANA registry.  Section 10.2 provides a mapping
   between the extensible attributes and their corresponding registry.
   Section 4.3 discusses the XML validation implications of this type of
   extension.  All extensible attributes that support private extensions
   also support public extensions.

5.2. Extending Classes

   Classes of the EXTENSION (iodef:ExtensionType) type can extend the
   data model.  They provide the ability to have new atomic or XML-
   encoded data elements in all of the top-level classes of the Incident
   class and in a few of the complex subordinate classes.  As there are
   multiple instances of the extensible classes in the data model, there
   is discretion on where to add a new data element.  It is RECOMMENDED
   that the extension be placed in the most closely related class to the
   new information.

   Extensions using the atomic data types (i.e., all values of the dtype
   attributes other than "xml") MUST:

   1.  Set the element content to the desired value, and

   2.  Set the dtype attribute to correspond to the data type of the
       element content.

   The following guidelines exist for extensions using XML (i.e.,
   dtype="xml"):

   1.  The element content of the extensible class MUST be set to the
       desired value, and the dtype attribute MUST be set to "xml".

   2.  The extension schema MUST declare a separate namespace.  It is
       RECOMMENDED that these extensions have the prefix "iodef-".  This
       recommendation makes readability of the document easier by
       allowing the reader to infer which namespaces relate to IODEF by
       inspection.

   3.  It is RECOMMENDED that extension schemas follow the naming
       convention of the IODEF data model.  This too improves the
       readability of extended IODEF documents.  The names of all
       elements SHOULD be capitalized.  For elements with composed
       names, a capital letter SHOULD be used for each word.  Attribute
       names SHOULD be in lowercase.  Attributes with composed names
       SHOULD be separated by a hyphen.

   4.  Implementations that encounter an unrecognized element,
       attribute, or attribute value in a supported namespace SHOULD
       reject the document as a syntax error.

   5.  There are security and performance implications in requiring
       implementations to dynamically download schemas at runtime.
       Therefore, implementations MUST NOT download schemas at runtime
       unless the appropriate precautions are taken.  Implementations
       also need to contend with the potential of significant network
       and processing issues.

   6.  Some adopters of the IODEF may have private schema definitions
       that are not publicly available.  Thus, implementations may
       encounter IODEF documents with references to private schemas that
       may not be resolvable.  Hence, IODEF document recipients MUST be
       prepared for a schema definition in an IODEF document never to
       resolve.

   The following schema and XML document excerpt provide a template for
   an extension schema and its use in the IODEF document.

   This example schema defines a namespace of "iodef-extension1" and a
   single element named "newdata".

     <xs:schema
        targetNamespace="iodef-extension1.xsd"
        xmlns:iodef-extension1="iodef-extension1.xsd"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">
        attributeFormDefault="unqualified"
        elementFormDefault="qualified">
      <xs:import
           namespace="urn:ietf:params:xml:ns:iodef-2.0"
           schemaLocation=" urn:ietf:params:xml:schema:iodef-2.0"/>

        <xs:element name="newdata" type="xs:string" />
     </xs:schema>

   The following XML excerpt demonstrates the use of the above schema as
   an extension to the IODEF.

        <IODEF-Document
             version="2.00" lang="en-US"
             xmlns="urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:iodef=" urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:iodef-extension1="iodef-extension1.xsd"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="iodef-extension1.xsd">
            <Incident purpose="reporting">
            ...
              <AdditionalData dtype="xml" meaning="xml">
                <iodef-extension1:newdata>
                 Field that could not be represented elsewhere
                </iodef-extension1:newdata>
              </AdditionalData>
            </Incident>
      </IODEF-Document>

5.3. Deconflicting Private Extensions

   To disambiguate which private extension is used in an IODEF document,
   the data model provides a means to identify the source of an
   extension.  Two attributes in the IODEF-Document class,
   private-enum-name and private-enum-id, are used to specify this
   attribution.  Only a single private extension can be identified in a
   given IODEF-Document.

   If an implementor has a single private extension, then only the
   private-enum-name attribute needs to be specified.  Multiple distinct
   private extensions or versioning of a single extension can be
   attributed by also setting the corresponding private-num-id
   attribute.

   The following XML excerpt demonstrates the specification of a private
   extension from "example.com" with an identifier of "13".

        <IODEF-Document
             version="2.00" lang="en-US"
             private-enum-name="example.com"
             private-enum-id="13" ...>
            ...
      </IODEF-Document>

   If an unrecognized private extension is encountered in processing,
   the recipient MAY reject the entire document as a syntax error.

6.  Internationalization Issues

   Internationalization and localization is of specific concern to the
   IODEF as it facilitates operational coordination with a diverse set
   of partners.  The IODEF implements internationalization by relying on
   XML constructs and through explicit design choices in the data model.

   Since the IODEF is implemented as an XML schema, it supports
   different character encodings, such as UTF-8 and UTF-16, that are
   possible with XML.  Additionally, each IODEF document MUST specify
   the language in which its content is encoded.  The language can be
   specified with the attribute "xml:lang" (per Section 2.12 of
   [W3C.XML]) in the top-level element (i.e., IODEF-Document) and lets
   all other elements inherit that definition.  All IODEF classes with a
   free-form text definition (i.e., all those defined with type
   iodef:MLStringType) can also specify a language different from the
   rest of the document.

   The data model supports multiple translations of free-form text.  All
   ML_STRING (iodef:MLStringType) classes have a one-to-many cardinality
   to their parent.  This allows the identical text translated into
   different languages to be encoded in different instances of the same
   class with a common parent.  This design also enables the creation of
   a single document containing all the translations.  The IODEF
   implementation SHOULD extract the appropriate language relevant to
   the recipient.

   Related instances of a given iodef:MLStringType class that are
   translations of each other are identified by a common identifier set
   in the translation-id attribute.  The example below shows three
   instances of a Description class expressed in three different
   languages.  The relationship between these three instances of the
   Description class is conveyed by the common value of "1" in the
   translation-id attribute.

   <IODEF-Document version="2.00" xml:lang="en" ...>
     <Incident purpose="reporting">
       ...
       <Description translation-id="1"
                    xml:lang="en">English</Description>
       <Description translation-id="1"
                    xml:lang="de">Englisch</Description>
       <Description translation-id="1"
                    xml:lang="fr">Anglais</Description>

   The IODEF balances internationalization support with the need for
   interoperability.  While the IODEF supports different languages, the
   data model also relies heavily on standardized enumerated attributes
   that can crudely approximate the contents of the document.  With this
   approach, a CSIRT should be able to make some sense of an IODEF
   document it receives even if the free-form text data elements are
   written in a language unfamiliar to the recipient.

7.  Examples

   This section provides examples of IODEF documents.  These examples do
   not represent the full capabilities of the data model or the only way
   to encode particular information.

7.1. Minimal Example

A document containing only the mandatory elements and attributes.

   <?xml version="1.0" encoding="UTF-8"?>
   
   <IODEF-Document version="2.00" xml:lang="en"
      xmlns="urn:ietf:params:xml:ns:iodef-2.0"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation=
   "http://www.iana.org/assignments/xml-registry/schema/
   iodef-2.0.xsd">
     <Incident purpose="reporting" restriction="private">
       <IncidentID name="csirt.example.com">492382</IncidentID>
       <GenerationTime>2015-07-18T09:00:00-05:00</GenerationTime>
       <Contact type="organization" role="creator">

<Email>
           <EmailTo>contact@csirt.example.com</EmailTo>
         </Email>
       </Contact>
       
     </Incident>
   </IODEF-Document>

7.2. Indicators from a Campaign

An example of C2 domains from a given campaign.

   <?xml version="1.0" encoding="UTF-8"?>
   
   <IODEF-Document version="2.00" xml:lang="en"
      xmlns="urn:ietf:params:xml:ns:iodef-2.0"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation=
      "http://www.iana.org/assignments/xml-registry/schema/
       iodef-2.0.xsd">
     <Incident purpose="watch" restriction="green">
       <IncidentID name="csirt.example.com">897923</IncidentID>
         <RelatedActivity>
           <ThreatActor>
             <ThreatActorID>
             TA-12-AGGRESSIVE-BUTTERFLY
             </ThreatActorID>
             <Description>Aggressive Butterfly</Description>
           </ThreatActor>
           <Campaign>
             <CampaignID>C-2015-59405</CampaignID>
             <Description>Orange Giraffe</Description>
           </Campaign>
         </RelatedActivity>
         <GenerationTime>2015-10-02T11:18:00-05:00</GenerationTime>
         <Description>Summarizes the Indicators of Compromise
           for the Orange Giraffe campaign of the Aggressive
           Butterfly crime gang.
         </Description>
         <Assessment>
           <BusinessImpact type="breach-proprietary"/>
         </Assessment>
         <Contact type="organization" role="creator">
           <ContactName>CSIRT for example.com</ContactName>
           <Email>
             <EmailTo>contact@csirt.example.com</EmailTo>
           </Email>
         </Contact>

         <IndicatorData>
           <Indicator>
             <IndicatorID name="csirt.example.com" version="1">
             G90823490
             </IndicatorID>
             <Description>C2 domains</Description>
             <StartTime>2014-12-02T11:18:00-05:00</StartTime>
             <Observable>
               <BulkObservable type="fqdn">
               <BulkObservableList>
                 kj290023j09r34.example.com
                 09ijk23jfj0k8.example.net
                 klknjwfjiowjefr923.example.org
                 oimireik79msd.example.org
               </BulkObservableList>
             </BulkObservable>
           </Observable>
         </Indicator>
       </IndicatorData>
     </Incident>
   </IODEF-Document>

8.  The IODEF Data Model (XML Schema)

  <?xml version="1.0"?>
  <xs:schema xmlns="urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:iodef="urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:enum="urn:ietf:params:xml:ns:iodef-enum-1.0"
             xmlns:sci="urn:ietf:params:xml:ns:iodef-sci-1.0"
             xmlns:xs="http://www.w3.org/2001/XMLSchema"
             xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
             targetNamespace="urn:ietf:params:xml:ns:iodef-2.0"
             elementFormDefault="qualified"
             attributeFormDefault="unqualified">
    <xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
               schemaLocation="http://www.w3.org/TR/2002/
  REC-xmldsig-core-20020212/xmldsig-core-schema.xsd"/>
    <xs:import namespace="urn:ietf:params:xml:ns:iodef-enum-1.0"
               schemaLocation="http://www.iana.org/assignments/
  xml-registry/schema/iodef-enum-1.0.xsd"/>
    <xs:import namespace="urn:ietf:params:xml:ns:iodef-sci-1.0"
               schemaLocation="http://www.iana.org/assignments/
  xml-registry/schema/iodef-sci-1.0.xsd"/>
    <xs:import namespace="http://www.w3.org/XML/1998/namespace"
               schemaLocation="http://www.w3c.org/2001/xml.xsd"/>
    <xs:annotation>
      <xs:documentation>
         Incident Object Description Exchange Format v2.0

</xs:documentation>
    </xs:annotation>
    
    <xs:element name="IODEF-Document">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Incident" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="version" type="xs:string" fixed="2.00"/>
        <xs:attribute ref="xml:lang"/>
        <xs:attribute name="format-id" type="xs:string" use="optional"/>
        <xs:attribute name="private-enum-name"
                      type="xs:string" use="optional"/>
        <xs:attribute name="private-enum-id"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Incident">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID"/>
          <xs:element ref="iodef:AlternativeID" minOccurs="0"/>
          <xs:element ref="iodef:RelatedActivity"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectTime" minOccurs="0"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:RecoveryTime" minOccurs="0"/>
          <xs:element ref="iodef:ReportTime" minOccurs="0"/>
          <xs:element ref="iodef:GenerationTime"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Discovery"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Assessment"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Method"

                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Contact" maxOccurs="unbounded"/>
          <xs:element ref="iodef:EventData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:IndicatorData" minOccurs="0"/>
          <xs:element ref="iodef:History" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="purpose"
                      type="incident-purpose-type" use="required"/>
        <xs:attribute name="ext-purpose"
                      type="xs:string" use="optional"/>
        <xs:attribute name="status" type="incident-status-type"/>
        <xs:attribute name="ext-status"
                      type="xs:string" use="optional"/>
        <xs:attribute ref="xml:lang"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" default="private"
                      use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="incident-purpose-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="traceback"/>
        <xs:enumeration value="mitigation"/>
        <xs:enumeration value="reporting"/>
        <xs:enumeration value="watch"/>
        <xs:enumeration value="other"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="incident-status-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="new"/>
        <xs:enumeration value="in-progress"/>
        <xs:enumeration value="forwarded"/>
        <xs:enumeration value="resolved"/>
        <xs:enumeration value="future"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>

<xs:element name="IncidentID" type="iodef:IncidentIDType"/>
    <xs:complexType name="IncidentIDType">
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="name" type="xs:string" use="required"/>
          <xs:attribute name="instance"
                        type="xs:string" use="optional"/>
          <xs:attribute name="restriction"
                        type="iodef:restriction-type" use="optional"/>
          <xs:attribute name="ext-restriction"
                        type="xs:string" use="optional"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
    
    <xs:element name="AlternativeID">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="RelatedActivity">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:ThreatActor"

                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Campaign"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:IndicatorID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="ThreatActor">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ThreatActorID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="ThreatActorID" type="xs:string"/>
    <xs:element name="Campaign">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:CampaignID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"

type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="CampaignID" type="xs:string"/>
    
    <xs:element name="Contact">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ContactName"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:ContactTitle"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:RegistryHandle"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:PostalAddress"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Email"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Telephone"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Timezone" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="role"
                      type="contact-role-type" use="required"/>
        <xs:attribute name="ext-role"
                      type="xs:string" use="optional"/>
        <xs:attribute name="type"
                      type="contact-type-type" use="required"/>
        <xs:attribute name="ext-type"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>

    <xs:simpleType name="contact-role-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="creator"/>
        <xs:enumeration value="reporter"/>
        <xs:enumeration value="admin"/>
        <xs:enumeration value="tech"/>
        <xs:enumeration value="provider"/>
        <xs:enumeration value="user"/>
        <xs:enumeration value="billing"/>
        <xs:enumeration value="legal"/>
        <xs:enumeration value="abuse"/>
        <xs:enumeration value="irt"/>
        <xs:enumeration value="cc"/>
        <xs:enumeration value="cc-irt"/>
        <xs:enumeration value="leo"/>
        <xs:enumeration value="vendor"/>
        <xs:enumeration value="vendor-services"/>
        <xs:enumeration value="victim"/>
        <xs:enumeration value="victim-notified"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="contact-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="person"/>
        <xs:enumeration value="organization"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="ContactName" type="iodef:MLStringType"/>
    <xs:element name="ContactTitle" type="iodef:MLStringType"/>
    <xs:element name="RegistryHandle">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="registry"
                          type="registryhandle-registry-type"/>
            <xs:attribute name="ext-registry"
                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="registryhandle-registry-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="internic"/>
        <xs:enumeration value="apnic"/>
        <xs:enumeration value="arin"/>

        <xs:enumeration value="lacnic"/>
        <xs:enumeration value="ripe"/>
        <xs:enumeration value="afrinic"/>
        <xs:enumeration value="local"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="PostalAddress">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:PAddress"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="postaladdress-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="PAddress" type="iodef:MLStringType"/>
    <xs:simpleType name="postaladdress-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="street"/>
        <xs:enumeration value="mailing"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Telephone">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:TelephoneNumber"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="telephone-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="TelephoneNumber" type="xs:string"/>
    <xs:simpleType name="telephone-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="wired"/>
        <xs:enumeration value="mobile"/>
        <xs:enumeration value="fax"/>
        <xs:enumeration value="hotline"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>

</xs:simpleType>
    <xs:element name="Email">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:EmailTo"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="email-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="email-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="direct"/>
        <xs:enumeration value="hotline"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    
    <xs:element name="DateTime" type="xs:dateTime"/>
    <xs:element name="ReportTime" type="xs:dateTime"/>
    <xs:element name="DetectTime" type="xs:dateTime"/>
    <xs:element name="StartTime" type="xs:dateTime"/>
    <xs:element name="EndTime" type="xs:dateTime"/>
    <xs:element name="RecoveryTime" type="xs:dateTime"/>
    <xs:element name="GenerationTime" type="xs:dateTime"/>
    <xs:element name="Timezone" type="iodef:TimezoneType"/>
    
    <xs:element name="History">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:HistoryItem" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>

</xs:element>
    <xs:element name="HistoryItem">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:DateTime"/>
          <xs:element ref="iodef:IncidentID" minOccurs="0"/>
          <xs:element ref="iodef:Contact" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DefinedCOA"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="action"
                      type="iodef:action-type" use="required"/>
        <xs:attribute name="ext-action"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="DefinedCOA" type="xs:string"/>
    
    <xs:element name="Expectation">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DefinedCOA"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:Contact" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="action"
                      type="iodef:action-type" default="other"/>
        <xs:attribute name="ext-action"
                      type="xs:string" use="optional"/>
        <xs:attribute name="severity" type="iodef:severity-type"/>
        <xs:attribute name="restriction"

type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Discovery">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectionPattern"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="source"
                      type="discovery-source-type" use="optional"
                      default="unknown"/>
        <xs:attribute name="ext-source"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="discovery-source-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="nidps"/>
        <xs:enumeration value="hips"/>
        <xs:enumeration value="siem"/>
        <xs:enumeration value="av"/>
        <xs:enumeration value="third-party-monitoring"/>
        <xs:enumeration value="incident"/>
        <xs:enumeration value="os-log"/>
        <xs:enumeration value="application-log"/>
        <xs:enumeration value="device-log"/>
        <xs:enumeration value="network-flow"/>
        <xs:enumeration value="passive-dns"/>
        <xs:enumeration value="investigation"/>
        <xs:enumeration value="audit"/>
        <xs:enumeration value="internal-notification"/>

<xs:enumeration value="external-notification"/>
        <xs:enumeration value="leo"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="actor"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="DetectionPattern">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Application"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element name="DetectionConfiguration"
                      type="xs:string"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Method">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Reference"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="sci:AttackPattern"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="sci:Vulnerability"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="sci:Weakness"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>

<xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Reference">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="enum:ReferenceName" minOccurs="0"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Assessment">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentCategory"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:choice maxOccurs="unbounded">
            <xs:element ref="iodef:SystemImpact"/>
            <xs:element ref="iodef:BusinessImpact"/>
            <xs:element ref="iodef:TimeImpact"/>
            <xs:element ref="iodef:MonetaryImpact"/>
            <xs:element ref="iodef:IntendedImpact"/>
          </xs:choice>
          <xs:element ref="iodef:Counter"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:MitigatingFactor"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Cause"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>

        <xs:attribute name="occurrence">
          <xs:simpleType>
            <xs:restriction base="xs:NMTOKEN">
              <xs:enumeration value="actual"/>
              <xs:enumeration value="potential"/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IncidentCategory" type="iodef:MLStringType"/>
    <xs:element name="BusinessImpact" type="iodef:BusinessImpactType"/>
    <xs:element name="IntendedImpact" type="iodef:BusinessImpactType"/>
    <xs:element name="MitigatingFactor" type="iodef:MLStringType"/>
    <xs:element name="Cause" type="iodef:MLStringType"/>
    <xs:element name="SystemImpact">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="severity"
                      type="iodef:severity-type" use="optional"/>
        <xs:attribute name="completion"
                      type="iodef:systemimpact-completion-type"
                      use="optional"/>
        <xs:attribute name="type"
                      type="systemimpact-type-type"
                      use="optional" default="unknown"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="systemimpact-completion-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="failed"/>
        <xs:enumeration value="succeeded"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="systemimpact-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="takeover-account"/>
        <xs:enumeration value="takeover-service"/>
        <xs:enumeration value="takeover-system"/>

        <xs:enumeration value="cps-manipulation"/>
        <xs:enumeration value="cps-damage"/>
        <xs:enumeration value="availability-data"/>
        <xs:enumeration value="availability-account"/>
        <xs:enumeration value="availability-service"/>
        <xs:enumeration value="availability-system"/>
        <xs:enumeration value="damaged-system"/>
        <xs:enumeration value="damaged-data"/>
        <xs:enumeration value="breach-proprietary"/>
        <xs:enumeration value="breach-privacy"/>
        <xs:enumeration value="breach-credential"/>
        <xs:enumeration value="breach-configuration"/>
        <xs:enumeration value="integrity-data"/>
        <xs:enumeration value="integrity-configuration"/>
        <xs:enumeration value="integrity-hardware"/>
        <xs:enumeration value="traffic-redirection"/>
        <xs:enumeration value="monitoring-traffic"/>
        <xs:enumeration value="monitoring-host"/>
        <xs:enumeration value="policy"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="BusinessImpactType">
      <xs:sequence>
        <xs:element ref="iodef:Description"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="severity"
                    type="businessimpact-severity-type" use="optional"/>
      <xs:attribute name="ext-severity"
                    type="xs:string" use="optional"/>
      <xs:attribute name="type"
                    type="businessimpact-type-type"
                    use="optional" default="unknown"/>
      <xs:attribute name="ext-type" type="xs:string" use="optional"/>
    </xs:complexType>
    <xs:simpleType name="businessimpact-severity-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="none"/>
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>
        <xs:enumeration value="high"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="businessimpact-type-type">

      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="breach-proprietary"/>
        <xs:enumeration value="breach-privacy"/>
        <xs:enumeration value="breach-credential"/>
        <xs:enumeration value="loss-of-integrity"/>
        <xs:enumeration value="loss-of-service"/>
        <xs:enumeration value="theft-financial"/>
        <xs:enumeration value="theft-service"/>
        <xs:enumeration value="degraded-reputation"/>
        <xs:enumeration value="asset-damage"/>
        <xs:enumeration value="asset-manipulation"/>
        <xs:enumeration value="legal"/>
        <xs:enumeration value="extortion"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="TimeImpact">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="iodef:PositiveFloatType">
            <xs:attribute name="severity" type="iodef:severity-type"/>
            <xs:attribute name="metric"
                          type="timeimpact-metric-type" use="required"/>
            <xs:attribute name="ext-metric"
                          type="xs:string" use="optional"/>
            <xs:attribute name="duration" type="iodef:duration-type"/>
            <xs:attribute name="ext-duration"
                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="timeimpact-metric-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="labor"/>
        <xs:enumeration value="elapsed"/>
        <xs:enumeration value="downtime"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="MonetaryImpact">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="iodef:PositiveFloatType">
            <xs:attribute name="severity" type="iodef:severity-type"/>
            <xs:attribute name="currency" type="xs:string"/>
          </xs:extension>

</xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:element name="Confidence">
      <xs:complexType>
        <xs:attribute name="rating"
                      type="confidence-rating-type" use="required"/>
        <xs:attribute name="ext-rating"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="confidence-rating-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>
        <xs:enumeration value="high"/>
        <xs:enumeration value="numeric"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    
    <xs:element name="EventData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectTime" minOccurs="0"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:RecoveryTime" minOccurs="0"/>
          <xs:element ref="iodef:ReportTime" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Discovery"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Assessment" minOccurs="0"/>
          <xs:element ref="iodef:Method"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Flow"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Expectation"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Record" minOccurs="0"/>

<xs:element ref="iodef:EventData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="Flow">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:System" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="System">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Node"/>
          <xs:element ref="iodef:NodeRole"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Service"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:OperatingSystem"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Counter"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element name="AssetID"
                      type="xs:string"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>
        <xs:attribute name="category" type="system-category-type"/>
        <xs:attribute name="ext-category"
                      type="xs:string" use="optional"/>
        <xs:attribute name="interface" type="xs:string"/>
        <xs:attribute name="spoofed"
                      type="yes-no-unknown-type" default="unknown"/>
        <xs:attribute name="virtual"
                      type="yes-no-unknown-type" use="optional"
                      default="unknown"/>
        <xs:attribute name="ownership" type="system-ownership-type"
                      use="optional"/>
        <xs:attribute name="ext-ownership"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="OperatingSystem" type="iodef:SoftwareType"/>
    <xs:simpleType name="system-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="source"/>
        <xs:enumeration value="target"/>
        <xs:enumeration value="intermediate"/>
        <xs:enumeration value="sensor"/>
        <xs:enumeration value="infrastructure"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="system-ownership-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="organization"/>
        <xs:enumeration value="personal"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="customer"/>
        <xs:enumeration value="no-relationship"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>

    <xs:element name="Node">
      <xs:complexType>
        <xs:sequence>
          <xs:choice maxOccurs="unbounded">
            <xs:element ref="iodef:DomainData"
                        minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="iodef:Address"
                        minOccurs="0" maxOccurs="unbounded"/>
          </xs:choice>
          <xs:element ref="iodef:PostalAddress" minOccurs="0"/>
          <xs:element ref="iodef:Location"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Counter"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Address">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="category"
                          type="address-category-type"
                          default="ipv6-addr"/>
            <xs:attribute name="ext-category"
                          type="xs:string" use="optional"/>
            <xs:attribute name="vlan-name" type="xs:string"/>
            <xs:attribute name="vlan-num" type="xs:integer"/>
            <xs:attribute name="observable-id"
                          type="xs:ID" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="address-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="asn"/>
        <xs:enumeration value="atm"/>
        <xs:enumeration value="e-mail"/>
        <xs:enumeration value="mac"/>
        <xs:enumeration value="ipv4-addr"/>
        <xs:enumeration value="ipv4-net"/>
        <xs:enumeration value="ipv4-net-masked"/>
        <xs:enumeration value="ipv4-net-mask"/>
        <xs:enumeration value="ipv6-addr"/>
        <xs:enumeration value="ipv6-net"/>
        <xs:enumeration value="ipv6-net-masked"/>
        <xs:enumeration value="site-uri"/>

        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Location" type="iodef:MLStringType"/>
    <xs:element name="NodeRole">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="category"
                      type="noderole-category-type" use="required"/>
        <xs:attribute name="ext-category"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="noderole-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="client"/>
        <xs:enumeration value="client-enterprise"/>
        <xs:enumeration value="client-partner"/>
        <xs:enumeration value="client-remote"/>
        <xs:enumeration value="client-kiosk"/>
        <xs:enumeration value="client-mobile"/>
        <xs:enumeration value="server-internal"/>
        <xs:enumeration value="server-public"/>
        <xs:enumeration value="www"/>
        <xs:enumeration value="mail"/>
        <xs:enumeration value="webmail"/>
        <xs:enumeration value="messaging"/>
        <xs:enumeration value="streaming"/>
        <xs:enumeration value="voice"/>
        <xs:enumeration value="file"/>
        <xs:enumeration value="ftp"/>
        <xs:enumeration value="p2p"/>
        <xs:enumeration value="name"/>
        <xs:enumeration value="directory"/>
        <xs:enumeration value="credential"/>
        <xs:enumeration value="print"/>
        <xs:enumeration value="application"/>
        <xs:enumeration value="database"/>
        <xs:enumeration value="backup"/>
        <xs:enumeration value="dhcp"/>
        <xs:enumeration value="assessment"/>
        <xs:enumeration value="source-control"/>
        <xs:enumeration value="config-management"/>
        <xs:enumeration value="monitoring"/>
        <xs:enumeration value="infra"/>

<xs:enumeration value="infra-firewall"/>
        <xs:enumeration value="infra-router"/>
        <xs:enumeration value="infra-switch"/>
        <xs:enumeration value="camera"/>
        <xs:enumeration value="proxy"/>
        <xs:enumeration value="remote-access"/>
        <xs:enumeration value="log"/>
        <xs:enumeration value="virtualization"/>
        <xs:enumeration value="pos"/>
        <xs:enumeration value="scada"/>
        <xs:enumeration value="scada-supervisory"/>
        <xs:enumeration value="sinkhole"/>
        <xs:enumeration value="honeypot"/>
        <xs:enumeration value="anonymization"/>
        <xs:enumeration value="c2-server"/>
        <xs:enumeration value="malware-distribution"/>
        <xs:enumeration value="drop-server"/>
        <xs:enumeration value="hop-point"/>
        <xs:enumeration value="reflector"/>
        <xs:enumeration value="phishing-site"/>
        <xs:enumeration value="spear-phishing-site"/>
        <xs:enumeration value="recruiting-site"/>
        <xs:enumeration value="fraudulent-site"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    
    <xs:element name="Service">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ServiceName" minOccurs="0"/>
          <xs:element ref="iodef:Port" minOccurs="0"/>
          <xs:element ref="iodef:Portlist" minOccurs="0"/>
          <xs:element ref="iodef:ProtoType" minOccurs="0"/>
          <xs:element ref="iodef:ProtoCode" minOccurs="0"/>
          <xs:element ref="iodef:ProtoField" minOccurs="0"/>
          <xs:element ref="iodef:ApplicationHeader" minOccurs="0"/>
          <xs:element ref="iodef:EmailData" minOccurs="0"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="ip-protocol"
                      type="xs:integer" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>

</xs:element>
    <xs:element name="Port" type="xs:integer"/>
    <xs:element name="Portlist" type="iodef:PortlistType"/>
    <xs:element name="ProtoType" type="xs:integer"/>
    <xs:element name="ProtoCode" type="xs:integer"/>
    <xs:element name="ProtoField" type="xs:integer"/>
    <xs:element name="ApplicationHeader">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ApplicationHeaderField"
                      maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="ApplicationHeaderField"
                type="iodef:ExtensionType"/>
    <xs:element name="ServiceName">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IANAService"
                      minOccurs="0"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="IANAService" type="xs:string"/>
    <xs:element name="Application" type="iodef:SoftwareType"/>
    
    <xs:element name="Counter">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:float">
            <xs:attribute name="type"
                          type="counter-type-type" use="required"/>
            <xs:attribute name="ext-type"
                          type="xs:string" use="optional"/>
            <xs:attribute name="unit"
                          type="counter-unit-type" use="required"/>
            <xs:attribute name="ext-unit"
                          type="xs:string" use="optional"/>
            <xs:attribute name="meaning"

type="xs:string" use="optional"/>
            <xs:attribute name="duration" type="iodef:duration-type"/>
            <xs:attribute name="ext-duration"
                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="counter-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="counter"/>
        <xs:enumeration value="rate"/>
        <xs:enumeration value="average"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="counter-unit-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="byte"/>
        <xs:enumeration value="mbit"/>
        <xs:enumeration value="packet"/>
        <xs:enumeration value="flow"/>
        <xs:enumeration value="session"/>
        <xs:enumeration value="event"/>
        <xs:enumeration value="alert"/>
        <xs:enumeration value="message"/>
        <xs:enumeration value="host"/>
        <xs:enumeration value="site"/>
        <xs:enumeration value="organization"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    
    <xs:element name="EmailData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:EmailTo"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:EmailFrom" minOccurs="0"/>
          <xs:element ref="iodef:EmailSubject" minOccurs="0"/>
          <xs:element ref="iodef:EmailX-Mailer" minOccurs="0"/>
          <xs:element ref="iodef:EmailHeaderField"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:EmailHeaders" minOccurs="0"/>

<xs:element ref="iodef:EmailBody" minOccurs="0"/>
          <xs:element ref="iodef:EmailMessage" minOccurs="0"/>
          <xs:element ref="iodef:HashData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="SignatureData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="EmailTo" type="xs:string"/>
    <xs:element name="EmailFrom" type="xs:string"/>
    <xs:element name="EmailSubject" type="xs:string"/>
    <xs:element name="EmailX-Mailer" type="xs:string"/>
    <xs:element name="EmailHeaderField" type="iodef:ExtensionType"/>
    <xs:element name="EmailHeaders" type="xs:string"/>
    <xs:element name="EmailBody" type="xs:string"/>
    <xs:element name="EmailMessage" type="xs:string"/>
    
    <xs:element name="DomainData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Name"/>
          <xs:element ref="iodef:DateDomainWasChecked"
                      minOccurs="0"/>
          <xs:element ref="iodef:RegistrationDate"
                      minOccurs="0"/>
          <xs:element ref="iodef:ExpirationDate"
                      minOccurs="0"/>
          <xs:element ref="iodef:RelatedDNS"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Nameservers"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DomainContacts"
                      minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="system-status"
                      type="domaindata-system-status-type"/>
        <xs:attribute name="ext-system-status"
                      type="xs:string" use="optional"/>
        <xs:attribute name="domain-status"
                      type="domaindata-domain-status-type"/>
        <xs:attribute name="ext-domain-status"
                      type="xs:string" use="optional"/>

        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Name" type="xs:string"/>
    <xs:element name="DateDomainWasChecked" type="xs:dateTime"/>
    <xs:element name="RegistrationDate" type="xs:dateTime"/>
    <xs:element name="ExpirationDate" type="xs:dateTime"/>
    <xs:simpleType name="domaindata-system-status-type">
      <xs:restriction base="xs:string">
        <xs:enumeration value="spoofed"/>
        <xs:enumeration value="fraudulent"/>
        <xs:enumeration value="innocent-hacked"/>
        <xs:enumeration value="innocent-hijacked"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="domaindata-domain-status-type">
      <xs:restriction base="xs:string">
        <xs:enumeration value="reservedDelegation"/>
        <xs:enumeration value="assignedAndActive"/>
        <xs:enumeration value="assignedAndInactive"/>
        <xs:enumeration value="assignedAndOnHold"/>
        <xs:enumeration value="revoked"/>
        <xs:enumeration value="transferPending"/>
        <xs:enumeration value="registryLock"/>
        <xs:enumeration value="registrarLock"/>
        <xs:enumeration value="other"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="RelatedDNS" type="iodef:ExtensionType"/>
    <xs:element name="Nameservers">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Server"/>
          <xs:element ref="iodef:Address" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Server" type="xs:string"/>
    <xs:element name="DomainContacts">
      <xs:complexType>
        <xs:choice>
          <xs:element ref="iodef:SameDomainContact"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="1" maxOccurs="unbounded"/>

</xs:choice>
      </xs:complexType>
    </xs:element>
    <xs:element name="SameDomainContact" type="xs:string"/>
    
    <xs:element name="Record">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:RecordData" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="RecordData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:DateTime" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
          <xs:element ref="iodef:RecordPattern"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:RecordItem"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:FileData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:WindowsRegistryKeysModified"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:CertificateData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>

</xs:element>
    <xs:element name="RecordPattern">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="type"
                          type="recordpattern-type-type"
                          use="required"/>
            <xs:attribute name="ext-type"
                          type="xs:string" use="optional"/>
            <xs:attribute name="offset"
                          type="xs:integer" use="optional"/>
            <xs:attribute name="offsetunit"
                          type="recordpattern-offsetunit-type"
                          use="optional" default="line"/>
            <xs:attribute name="ext-offsetunit"
                          type="xs:string" use="optional"/>
            <xs:attribute name="instance"
                          type="xs:integer" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="recordpattern-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="regex"/>
        <xs:enumeration value="binary"/>
        <xs:enumeration value="xpath"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="recordpattern-offsetunit-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="line"/>
        <xs:enumeration value="byte"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="RecordItem" type="iodef:ExtensionType"/>
    
    <xs:element name="WindowsRegistryKeysModified">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Key" maxOccurs="unbounded"/>

</xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Key">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:KeyName"/>
          <xs:element ref="iodef:Value" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="registryaction"
                      type="key-registryaction-type"/>
        <xs:attribute name="ext-registryaction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="KeyName" type="xs:string"/>
    <xs:element name="Value" type="xs:string"/>
    <xs:simpleType name="key-registryaction-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="add-key"/>
        <xs:enumeration value="add-value"/>
        <xs:enumeration value="delete-key"/>
        <xs:enumeration value="delete-value"/>
        <xs:enumeration value="modify-key"/>
        <xs:enumeration value="modify-value"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    
    <xs:element name="FileData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:File"
                      minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>

<xs:element name="File">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:FileName" minOccurs="0"/>
          <xs:element ref="iodef:FileSize" minOccurs="0"/>
          <xs:element ref="FileType" minOccurs="0"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:HashData" minOccurs="0"/>
          <xs:element ref="iodef:SignatureData" minOccurs="0"/>
          <xs:element ref="iodef:AssociatedSoftware" minOccurs="0"/>
          <xs:element ref="iodef:FileProperties"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="FileName" type="xs:string"/>
    <xs:element name="FileSize" type="xs:integer"/>
    <xs:element name="FileType" type="xs:string"/>
    <xs:element name="AssociatedSoftware" type="iodef:SoftwareType"/>
    <xs:element name="FileProperties" type="iodef:ExtensionType"/>
    
    <xs:element name="HashData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:HashTargetID" minOccurs="0"/>
          <xs:element ref="iodef:Hash"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:FuzzyHash"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="scope"
                      type="hashdata-scope-type" use="required"/>
        <xs:attribute name="ext-scope" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="HashTargetID" type="xs:string"/>
    <xs:simpleType name="hashdata-scope-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="file-contents"/>
        <xs:enumeration value="file-pe-section"/>
        <xs:enumeration value="file-pe-iat"/>
        <xs:enumeration value="file-pe-resource"/>

<xs:enumeration value="file-pdf-object"/>
        <xs:enumeration value="email-hash"/>
        <xs:enumeration value="email-headers-hash"/>
        <xs:enumeration value="email-body-hash"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Hash">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="ds:DigestMethod"/>
          <xs:element ref="ds:DigestValue"/>
          <xs:element ref="ds:CanonicalizationMethod"
                      minOccurs="0"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="FuzzyHash">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:FuzzyHashValue"
                      maxOccurs="unbounded"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="FuzzyHashValue" type="iodef:ExtensionType"/>
    
    <xs:element name="SignatureData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="ds:Signature" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="CertificateData">

<xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Certificate" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Certificate">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="ds:X509Data"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    
    <xs:element name="IndicatorData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Indicator"
                      minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Indicator">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IndicatorID"/>
          <xs:element ref="iodef:AlternativeIndicatorID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:choice>

            <xs:element ref="iodef:Observable"/>
            <xs:element ref="iodef:ObservableReference"/>
            <xs:element ref="iodef:IndicatorExpression"/>
            <xs:element ref="iodef:IndicatorReference"/>
          </xs:choice>
          <xs:element ref="iodef:NodeRole"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AttackPhase"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Reference"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IndicatorID">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:ID">
            <xs:attribute name="name" type="xs:string" use="required"/>
            <xs:attribute name="version"
                          type="xs:string" use="required"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:element name="AlternativeIndicatorID">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IndicatorID" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Observable">
      <xs:complexType>
        <xs:choice>
          <xs:element ref="iodef:System" minOccurs="0"/>
          <xs:element ref="iodef:Address" minOccurs="0"/>
          <xs:element ref="iodef:DomainData" minOccurs="0"/>

          <xs:element ref="iodef:Service" minOccurs="0"/>
          <xs:element ref="iodef:EmailData" minOccurs="0"/>
          <xs:element ref="iodef:WindowsRegistryKeysModified"
                           minOccurs="0"/>
          <xs:element ref="iodef:FileData" minOccurs="0"/>
          <xs:element ref="iodef:CertificateData" minOccurs="0"/>
          <xs:element ref="iodef:RegistryHandle" minOccurs="0"/>
          <xs:element ref="iodef:RecordData" minOccurs="0"/>
          <xs:element ref="iodef:EventData" minOccurs="0"/>
          <xs:element ref="iodef:Incident" minOccurs="0"/>
          <xs:element ref="iodef:Expectation" minOccurs="0"/>
          <xs:element ref="iodef:Reference" minOccurs="0"/>
          <xs:element ref="iodef:Assessment" minOccurs="0"/>
          <xs:element ref="iodef:DetectionPattern" minOccurs="0"/>
          <xs:element ref="iodef:HistoryItem" minOccurs="0"/>
          <xs:element ref="iodef:BulkObservable" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:choice>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="BulkObservable">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:BulkObservableFormat" minOccurs="0"/>
          <xs:element name="BulkObservableList"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="bulkobservable-type-type" use="required"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="bulkobservable-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="asn"/>
        <xs:enumeration value="atm"/>
        <xs:enumeration value="e-mail"/>
        <xs:enumeration value="ipv4-addr"/>
        <xs:enumeration value="ipv4-net"/>
        <xs:enumeration value="ipv4-net-mask"/>
        <xs:enumeration value="ipv6-addr"/>
        <xs:enumeration value="ipv6-net"/>

        <xs:enumeration value="ipv6-net-mask"/>
        <xs:enumeration value="mac"/>
        <xs:enumeration value="site-uri"/>
        <xs:enumeration value="domain-name"/>
        <xs:enumeration value="domain-to-ipv4"/>
        <xs:enumeration value="domain-to-ipv6"/>
        <xs:enumeration value="domain-to-ipv4-timestamp"/>
        <xs:enumeration value="domain-to-ipv6-timestamp"/>
        <xs:enumeration value="ipv4-port"/>
        <xs:enumeration value="ipv6-port"/>
        <xs:enumeration value="windows-reg-key"/>
        <xs:enumeration value="file-hash"/>
        <xs:enumeration value="email-x-mailer"/>
        <xs:enumeration value="email-subject"/>
        <xs:enumeration value="http-user-agent"/>
        <xs:enumeration value="http-request-uri"/>
        <xs:enumeration value="mutex"/>
        <xs:enumeration value="file-path"/>
        <xs:enumeration value="user-name"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="BulkObservableFormat">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Hash" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="BulkObservableList" type="xs:string"/>
    <xs:element name="IndicatorExpression">
      <xs:complexType>
        <xs:sequence maxOccurs="unbounded">
          <xs:choice>
            <xs:element ref="iodef:IndicatorExpression"/>
            <xs:element ref="iodef:Observable"/>
            <xs:element ref="iodef:ObservableReference"/>
            <xs:element ref="iodef:IndicatorReference"/>
          </xs:choice>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="operator"
                      type="indicatorexpression-operator-type"
                      use="optional" default="and"/>
        <xs:attribute name="ext-operator"

type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="indicatorexpression-operator-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="not"/>
        <xs:enumeration value="and"/>
        <xs:enumeration value="or"/>
        <xs:enumeration value="xor"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="ObservableReference">
      <xs:complexType>
        <xs:attribute name="uid-ref" type="xs:IDREF" use="required"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IndicatorReference">
      <xs:complexType>
        <xs:attribute name="uid-ref" type="xs:IDREF" use="optional"/>
        <xs:attribute name="euid-ref" type="xs:string" use="optional"/>
        <xs:attribute name="version" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="AttackPhase">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:AttackPhaseID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="AttackPhaseID" type="xs:string"/>
    
    <xs:element name="AdditionalData" type="iodef:ExtensionType"/>
    <xs:element name="Description" type="iodef:MLStringType"/>
    <xs:element name="URL" type="xs:anyURI"/>

<xs:simpleType name="PositiveFloatType">
      <xs:restriction base="xs:float">
        <xs:minExclusive value="0"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="MLStringType">
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="translation-id"
                        type="xs:string" use="optional"/>
          <xs:attribute ref="xml:lang"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
    <xs:simpleType name="PortlistType">
      <xs:restriction base="xs:string">
        <xs:pattern value="\d+(\-\d+)?(,\d+(\-\d+)?)*"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="TimezoneType">
      <xs:restriction base="xs:string">
        <xs:pattern
         value="Z|[\+\-](0[0-9]|1[0-4]):[0-5][0-9]"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="ExtensionType" mixed="true">
      <xs:sequence>
        <xs:any namespace="##any" processContents="lax"
                minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>

      <xs:attribute name="name" type="xs:string" use="optional"/>
      <xs:attribute name="dtype"
                    type="iodef:dtype-type" use="required"/>
      <xs:attribute name="ext-dtype" type="xs:string" use="optional"/>
      <xs:attribute name="meaning" type="xs:string" use="optional"/>
      <xs:attribute name="formatid" type="xs:string" use="optional"/>
      <xs:attribute name="restriction"
                    type="iodef:restriction-type" use="optional"/>
      <xs:attribute name="ext-restriction"
                    type="xs:string" use="optional"/>
      <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
    </xs:complexType>

<xs:complexType name="SoftwareType">
      <xs:sequence>
        <xs:element ref="iodef:SoftwareReference" minOccurs="0"/>
        <xs:element ref="iodef:URL"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element ref="iodef:Description"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
    <xs:element name="SoftwareReference">
      <xs:complexType>
        <xs:sequence>
          <xs:any namespace="##any" processContents="lax"
                  minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="spec-name"
                      type="softwarereference-spec-name-type"
                      use="required"/>
        <xs:attribute name="ext-spec-name"
                      type="xs:string" use="optional"/>
        <xs:attribute name="dtype"
                      type="softwarereference-dtype-type"
                      use="optional"/>
        <xs:attribute name="ext-dtype" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="softwarereference-spec-name-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="custom"/>
        <xs:enumeration value="cpe"/>
        <xs:enumeration value="swid"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="softwarereference-dtype-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="bytes"/>
        <xs:enumeration value="integer"/>
        <xs:enumeration value="real"/>
        <xs:enumeration value="string"/>
        <xs:enumeration value="xml"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     == Global attribute type declarations                            ==
     ===================================================================

    -->
    <xs:simpleType name="yes-no-unknown-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="yes"/>
        <xs:enumeration value="no"/>
        <xs:enumeration value="unknown"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="restriction-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="default"/>
        <xs:enumeration value="public"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="need-to-know"/>
        <xs:enumeration value="private"/>
        <xs:enumeration value="white"/>
        <xs:enumeration value="green"/>
        <xs:enumeration value="amber"/>
        <xs:enumeration value="red"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="severity-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>
        <xs:enumeration value="high"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="duration-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="second"/>
        <xs:enumeration value="minute"/>
        <xs:enumeration value="hour"/>
        <xs:enumeration value="day"/>
        <xs:enumeration value="month"/>
        <xs:enumeration value="quarter"/>
        <xs:enumeration value="year"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="action-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="nothing"/>
        <xs:enumeration value="contact-source-site"/>
        <xs:enumeration value="contact-target-site"/>
        <xs:enumeration value="contact-sender"/>
        <xs:enumeration value="investigate"/>

        <xs:enumeration value="block-host"/>
        <xs:enumeration value="block-network"/>
        <xs:enumeration value="block-port"/>
        <xs:enumeration value="rate-limit-host"/>
        <xs:enumeration value="rate-limit-network"/>
        <xs:enumeration value="rate-limit-port"/>
        <xs:enumeration value="redirect-traffic"/>
        <xs:enumeration value="honeypot"/>
        <xs:enumeration value="upgrade-software"/>
        <xs:enumeration value="rebuild-asset"/>
        <xs:enumeration value="harden-asset"/>
        <xs:enumeration value="remediate-other"/>
        <xs:enumeration value="status-triage"/>
        <xs:enumeration value="status-new-info"/>
        <xs:enumeration value="watch-and-report"/>
        <xs:enumeration value="defined-coa"/>
        <xs:enumeration value="other"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="dtype-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="boolean"/>
        <xs:enumeration value="byte"/>
        <xs:enumeration value="bytes"/>
        <xs:enumeration value="character"/>
        <xs:enumeration value="date-time"/>
        <xs:enumeration value="integer"/>
        <xs:enumeration value="ntpstamp"/>
        <xs:enumeration value="portlist"/>
        <xs:enumeration value="real"/>
        <xs:enumeration value="string"/>
        <xs:enumeration value="file"/>
        <xs:enumeration value="path"/>
        <xs:enumeration value="frame"/>
        <xs:enumeration value="packet"/>
        <xs:enumeration value="ipv4-packet"/>
        <xs:enumeration value="ipv6-packet"/>
        <xs:enumeration value="url"/>
        <xs:enumeration value="csv"/>
        <xs:enumeration value="winreg"/>
        <xs:enumeration value="xml"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:schema>

9.  Security Considerations

   The IODEF data model does not directly introduce security or privacy
   issues.  However, as the data encoded by the IODEF might be
   considered sensitive by the parties exchanging it or by those
   described by it, care needs to be taken to ensure appropriate
   handling during the document construction, exchange, processing,
   archiving, subsequent retrieval, and analysis.

9.1. Security

   The underlying messaging format and protocol used to exchange
   instances of the IODEF MUST provide appropriate guarantees of
   confidentiality, integrity, and authenticity.  The use of a
   standardized security protocol is encouraged.  The Real-time Inter-
   network Defense (RID) protocol [RFC6545] and its associated transport
   binding IODEF/RID over HTTP/TLS [RFC6546] provide such security.

   An IODEF implementation may act on the data in the document.  These
   actions might be explicitly requested in the document or the result
   of analytical logic that triggered on data in the document.  For this
   reason, care must be taken by IODEF implementations to properly
   authenticate the sender and receiver of the document.  The sender
   needs confidence that sensitive information and timely requests for
   action are sent to the correct recipient.  The recipient may
   interpret the contents of the document differently based on who sent
   it or vary actions based on the sender.  While the sender of the
   document may explicitly convey confidence in the data in a granular
   way using the Confidence class, the recipient is free to ignore or
   refine this information to make its own assessment.  Ambiguous
   Confidence elements (where it is unclear to which of a set of other
   elements the Confidence element relates) in a document MUST be
   ignored by the recipient.

   Certain classes may require out-of-band coordination to agree upon
   their semantics (e.g., Confidence@rating="low" or DefinedCOA).  This
   coordination MUST occur prior to operational data exchange to prevent
   the incorrect interpretation of these select data elements.  When
   parsing these data elements, implementations should validate, when
   possible, that they conform to the agreed upon semantics.  These
   semantics may need to be periodically reevaluated.

   Executable content of various forms could be embedded into the IODEF
   document directly or through an extension.  Implementation MUST
   handle this content with care to prevent unintentional automated
   execution.  The following classes are explicitly intended to
   represent content that might be executable:

   o  All classes of type iodef:ExtensionType and the RecordPattern
      class can represent arbitrary binary strings such as legitimate
      software programs or malware.

   o  The EmailMessage and EmailBody classes can represent email
      attachments that can contain arbitrary content.

   o  The DetectionPattern class could specify a machine-readable
      configuration that directs the execution of the corresponding
      tool.

   Per Section 4.3, IODEF implementations will need to periodically
   consult the IANA registries specified in Section 10.2 to discover
   newly registered enumerated attribute values.  These implementations
   MUST communicate with IANA in a way that ensures the integrity of the
   values and the authenticity of the source.  HTTPS over TLS
   [RFC2818][RFC5246] provides such security.

9.2. Privacy

   The IODEF contains numerous fields that are identifiers that could be
   linked to an individual or organization.  IODEF documents may contain
   sensitive information about these identified parties; repeated
   document exchanges about the same and related parties may enable the
   correlation of data about them.  Likewise, a party may report on
   another to a third party without their knowledge.

   When creating an IODEF document, careful consideration must be given
   to what information is shared.  Personal identifiers and attributable
   sensitive information should only be shared when necessary.

   When exchanging documents, transport security MUST provide document-
   level confidentiality.  XML element-level confidentiality can also be
   provided by using [W3C.XMLENC].

   In order to suggest data processing and handling guidelines of the
   encoded information, the IODEF allows a document sender to convey a
   privacy policy using the restriction attribute.  The various
   instances of this attribute allow different data elements of the
   document to be covered by dissimilar policies.  While flexible, it
   must be stressed that this approach only serves as a guideline from
   the sender, as the recipient is free to ignore it.

   Although outside of the scope of an IODEF implementation, the
   contents of IODEF documents and any derived analysis should be
   archived with appropriate confidentiality controls.  Likewise, access
   to retrieve and analyze this data should be restricted to authorized
   users.

10.  IANA Considerations

   This document registers a namespace, an XML schema, and a number of
   registries that map to enumerated values defined in the data model.
   It also defines an Expert Review process for IODEF-related XML
   registry entries.

10.1. Namespace and Schema

   This document uses URNs to describe an XML namespace and schema
   conforming to a registry mechanism described in [RFC3688].

   Registration for the IODEF namespace:

   o  URI: urn:ietf:params:xml:ns:iodef-2.0

   o  Registrant Contact: See the author in the "Author's Address"
      section of this document.

   o  XML: None.  Namespace URIs do not represent an XML specification.

   Registration for the IODEF XML schema:

   o  URI: urn:ietf:params:xml:schema:iodef-2.0

   o  Registrant Contact: See the first author of the "Author's Address"
      section of this document.

   o  XML: See Section 8 of this document.

10.2. Enumerated Value Registries

   This document creates 34 identically structured registries to be
   managed by IANA:

   o  Name of the parent registry: "Incident Object Description Exchange
      Format v2 (IODEF)"

   o  URL of the registry: <http://www.iana.org/assignments/iodef2>

   o  Namespace format: A registry entry consists of:

      *  Value.  A value for a given IODEF attribute.  It MUST conform
         to the formatting specified by the IODEF ENUM data type which
         is implemented as an "xs:NMTOKEN" type per Section 3.3.4 of
         [W3C.SCHEMA.DTYPES].  The value SHOULD conform to the
         convention specified in Section 5.2.

      *  Description.  A short description of the enumerated value.

      *  Reference.  An optional list of URIs to further describe the
         value.

   o  Allocation policy: Expert Review per [RFC5226].  This reviewer
      will ensure that the requested registry entry conforms to the
      prescribed formatting.  The reviewer will also ensure that the
      entry is an appropriate value for the attribute per the
      information model (Section 3).

   The registries to be created are named in the "Registry Name" column
   of Table 1.  Each registry is initially populated with values and
   descriptions that come from an attribute specified in the IODEF
   schema (Section 8) whose description is found in a sub-section of the
   information model (Section 3).  The initial values for the Value and
   Description fields of a given registry are listed in the "IV (Value)"
   and "IV (Desc.)" columns, respectively.  The "IV (Value)" points to a
   given schema type per Section 8.  Each enumerated value in the schema
   gets a corresponding entry in a given registry.  The "IV (Desc.)"
   points to a section in the text of this document that describes each
   enumerated value.  The initial value of the Reference field of every
   registry entry described below should be this document.

10.3. Expert Review of IODEF-Related XML Registry Entries

   IODEF class extensions, per Section 5.2, could register their
   namespaces and schemas with the IANA XML namespace ("ns" on
   <http://www.iana.org/assignments/xml-registry/>) and schema
   registries ("schema" on <http://www.iana.org/assignments/
   xml-registry/>) described in [RFC3688].  In addition to any reviews
   required by IANA, changes to the XML "schema" registry for schema
   names beginning with "urn:ietf:params:xml:schema:iodef" are subject
   to an additional IODEF Expert Review [RFC5226] to ensure
   compatibility with IODEF and other existing IODEF extensions.

   The IODEF expert(s) for these reviews will be designated by the IETF
   Security Area Directors.

   This document obsoletes [RFC6685].

11.  References

11.1. Normative References

   [E.164]    ITU Telecommunication Standardization Sector, "The
              International Public Telecommunication Numbering Plan",
              ITU-T Recommendation E.164, November 2010.

   [IANA.Media]
              IANA, "Media Types",
              <http://www.iana.org/assignments/media-types/>.

   [IANA.Ports]
              IANA, "Service Name and Transport Protocol Port Number
              Registry", <http://www.iana.org/assignments/
              service-names-port-numbers/>.

   [IANA.Protocols]
              IANA, "Assigned Internet Protocol Numbers",
              <http://www.iana.org/assignments/protocol-numbers/>.

   [IEEE.POSIX]
              IEEE, "Information Technology - Portable Operating System
              Interface (POSIX) Base Specifications, Issue 7", IEEE
              Std 1003.1-2001, DOI 10.1109/IEEESTD.2009.5393893,
              September 2009.

   [ISO19770] International Organization for Standardization,
              "Information technology -- Software asset management --
              Part 2: Software identification tag", ISO
              Standard 19770-2:2015, October 2015.

   [ISO4217]  International Organization for Standardization, "Codes for
              the representation of currencies", ISO 4217:2015, 2015.

   [NIST.CPE] Cheikes, B., Waltermire, D., and K. Scarfone, "Common
              Platform Enumeration: Naming Specification Version 2.3",
              NIST Interagency Report 7695, August 2011,
              <http://csrc.nist.gov/publications/nistir/ir7695/
              NISTIR-7695-CPE-Naming.pdf>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2781]  Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO
              10646", RFC 2781, DOI 10.17487/RFC2781, February 2000,
              <http://www.rfc-editor.org/info/rfc2781>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <http://www.rfc-editor.org/info/rfc3629>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <http://www.rfc-editor.org/info/rfc4291>.

   [RFC4519]  Sciberras, A., Ed., "Lightweight Directory Access Protocol
              (LDAP): Schema for User Applications", RFC 4519,
              DOI 10.17487/RFC4519, June 2006,
              <http://www.rfc-editor.org/info/rfc4519>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <http://www.rfc-editor.org/info/rfc5322>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <http://www.rfc-editor.org/info/rfc5646>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <http://www.rfc-editor.org/info/rfc5952>.

   [RFC6531]  Yao, J. and W. Mao, "SMTP Extension for Internationalized
              Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
              <http://www.rfc-editor.org/info/rfc6531>.

   [RFC7203]  Takahashi, T., Landfield, K., and Y. Kadobayashi, "An
              Incident Object Description Exchange Format (IODEF)
              Extension for Structured Cybersecurity Information",
              RFC 7203, DOI 10.17487/RFC7203, April 2014,
              <http://www.rfc-editor.org/info/rfc7203>.

   [RFC7495]  Montville, A. and D. Black, "Enumeration Reference Format
              for the Incident Object Description Exchange Format
              (IODEF)", RFC 7495, DOI 10.17487/RFC7495, March 2015,
              <http://www.rfc-editor.org/info/rfc7495>.

   [W3C.SCHEMA]
              Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,
              "XML Schema Part 1: Structures Second Edition", W3C
              Recommendation REC-xmlschema-1-20041028, October 2004,
              <http://www.w3.org/TR/xmlschema-1/>.

   [W3C.SCHEMA.DTYPES]
              Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
              Second Edition", W3C Recommendation REC-xmlschema-
              2-20041028, October 2004,
              <http://www.w3.org/TR/xmlschema-2/>.

   [W3C.XML]  Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", W3C Recommendation REC-xml-20081126, November
              2008, <http://www.w3.org/TR/2008/REC-xml-20081126/>.

   [W3C.XMLNS]
              Bray, T., Hollander, D., Layman, A., Tobin, R., and H.
              Thompson, "Namespaces in XML 1.0 (Third Edition)", W3C
              Recommendation REC-xml-names-20091208, December 2009,
              <http://www.w3.org/TR/2009/REC-xml-names-20091208/>.

   [W3C.XMLSIG]
              Eastlake, D., Reagle, J., Solo, D., Hirsch, F., and T.
              Roessler, "XML Signature Syntax and Processing (Second
              Edition)", W3C Recommendation REC-xmldsig-core-20080610,
              June 2008, <http://www.w3.org/TR/xmldsig-core/>.

   [W3C.XPATH]
              Robie, J., Dyck, M., and J. Spiegel, "XML Path Language
              (XPath) 3.1", W3C Candidate Recommendation CR-xpath-
              31-20151217, December 2015,
              <https://www.w3.org/TR/xpath-3/>.

11.2. Informative References

   [KB310516] Microsoft Corporation, "How to add, modify, or delete
              registry subkeys and values by using a .reg file",
              September 2013,
              <https://support.microsoft.com/en-us/kb/310516>.

   [NIST800.61rev2]
              National Institute of Standards and Technology, "Computer
              Security Incident Handling Guide", NIST Special
              Publication 800-61, Revision 2, August 2012,
              <http://dx.doi.org/10.6028/NIST.SP.800-61r2>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC3982]  Newton, A. and M. Sanz, "IRIS: A Domain Registry (dreg)
              Type for the Internet Registry Information Service
              (IRIS)", RFC 3982, DOI 10.17487/RFC3982, January 2005,
              <http://www.rfc-editor.org/info/rfc3982>.

   [RFC4180]  Shafranovich, Y., "Common Format and MIME Type for Comma-
              Separated Values (CSV) Files", RFC 4180,
              DOI 10.17487/RFC4180, October 2005,
              <http://www.rfc-editor.org/info/rfc4180>.

   [RFC5070]  Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
              Object Description Exchange Format", RFC 5070,
              DOI 10.17487/RFC5070, December 2007,
              <http://www.rfc-editor.org/info/rfc5070>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5901]  Cain, P. and D. Jevans, "Extensions to the IODEF-Document
              Class for Reporting Phishing", RFC 5901,
              DOI 10.17487/RFC5901, July 2010,
              <http://www.rfc-editor.org/info/rfc5901>.

   [RFC6545]  Moriarty, K., "Real-time Inter-network Defense (RID)",
              RFC 6545, DOI 10.17487/RFC6545, April 2012,
              <http://www.rfc-editor.org/info/rfc6545>.

   [RFC6546]  Trammell, B., "Transport of Real-time Inter-network
              Defense (RID) Messages over HTTP/TLS", RFC 6546,
              DOI 10.17487/RFC6546, April 2012,
              <http://www.rfc-editor.org/info/rfc6546>.

   [RFC6685]  Trammell, B., "Expert Review for Incident Object
              Description Exchange Format (IODEF) Extensions in IANA XML
              Registry", RFC 6685, DOI 10.17487/RFC6685, July 2012,
              <http://www.rfc-editor.org/info/rfc6685>.

   [W3C.XMLENC]
              Eastlake, D., Reagle, J., Solo, D., Hirsch, F., Nystrom,
              M., Roessler, T., and K. Yiu, "XML Encryption Syntax and
              Processing Version 1.1", W3C Recommendation REC-xmldsig-
              core1-20130411, April 2013,
              <https://www.w3.org/TR/xmlenc-core1/>.

Acknowledgments

   Thanks to Paul Stoecker for his editorial leadership in the
   transition of an early draft to the current document.

   Thanks to Kathleen Moriarty, Brian Trammel, Alexey Melnikov, Takeshi
   Takahashi, David Waltermire, and Sean Turner (as the MILE working
   group chairs, secretary, and area directors) for providing feedback
   and coordination of this document.

   Thanks to the following individuals (listed alphabetically) who
   provided feedback during the meetings, on the mailing list, or
   through implementation experience: Jerome Athias, David Black, Eric
   Burger, Toma Cejka, Patrick Curry, John Field, Christopher
   Harrington, Chris Inacio, Panos Kampanakis, David Misell, Daisuke
   Miyamoto, Adam Montville, Robert Moskowitz, Lagadec Philippe, Tony
   Rutkowski, Mio Suzuki, and Nik Teague.

Author's Address

   Roman Danyliw
   CERT
   Software Engineering Institute
   Carnegie Mellon University
   4500 Fifth Avenue
   Pittsburgh, PA
   United States of America

   Email: rdd@cert.org

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction

1.1. Terminology

1.2. Notations

1.3. About the IODEF Data Model

1.4. Changes from RFC 5070

2. IODEF Data Types

2.1. Integers

2.2. Real Numbers

2.3. Characters and Strings

2.4. Multilingual Strings

2.5. Binary Strings

2.5.1. Base64 Bytes

2.5.2. Hexadecimal Bytes

2.6. Enumerated Types

2.7. Date-Time String

2.8. Timezone String

2.9. Port Lists

2.10. Postal Address

2.11. Telephone Number

2.12. Email String

2.13. Uniform Resource Locator Strings

2.14. Identifiers and Identifier References

2.15. Software

2.15.1. SoftwareReference Class

3. swid. The element content describes a software identification (SWID) tag per [ISO19770].

4. string. The element content is of type STRING.

5. xml. The element content is XML. See Section 5.2.

2.16. Extension

6. ntpstamp. Same as date-time.

7. integer. The element content is of type INTEGER.

8. portlist. The element content is of type PORTLIST.

9. real. The element content is of type REAL.

10. string. The element content is of type STRING.

11. file. The element content is a base64-encoded binary file encoded as a BYTE[] type.

12. path. The element content is a file-system path encoded as a STRING type.

13. frame. The element content is a Layer 2 frame encoded as a HEXBIN type.

14. packet. The element content is a Layer 3 packet encoded as a HEXBIN type.

15. ipv4-packet. The element content is an IPv4 packet encoded as a HEXBIN type.

16. ipv6-packet. The element content is an IPv6 packet encoded as a HEXBIN type.

17. url. The element content is of type URL.

18. csv. The element content is a comma-separated value (CSV) list per Section 2 of [RFC4180] encoded as a STRING type.

19. winreg. The element content is a Microsoft Windows registry key encoded as a STRING type.

20. xml. The element content is XML. See Section 5.2.

3.1. IODEF-Document Class

3.2. Incident Class

3.3. Common Attributes

3.3.1. restriction Attribute

3.3.2. observable-id Attribute

3.4. IncidentID Class

3.5. AlternativeID Class

3.6. RelatedActivity Class

3.7. ThreatActor Class

3.8. Campaign Class

3.9. Contact Class

3.9.1. RegistryHandle Class

3.9.2. PostalAddress Class

3.9.3. Email Class

3.9.4. Telephone Class

3.10. Discovery Class

3.10.1. DetectionPattern Class

3.11. Method Class

3.11.1. Reference Class

3.12. Assessment Class

3.12.1. SystemImpact Class

21. monitoring-host. System activity (e.g., running processes, keystrokes) were monitored.

22. policy. Activity violated the system owner's acceptable use policy.

23. unknown. The impact is unknown.

3.12.2. BusinessImpact Class

3.12.3. TimeImpact Class

3.12.4. MonetaryImpact Class

3.12.5. Confidence Class

3.13. History Class

3.13.1. HistoryItem Class

3.14. EventData Class

3.14.1. Relating the Incident and EventData Classes

3.14.2. Recursive Definition of EventData

3. swid. The element content describes a software identification
(SWID) tag per [ISO19770].

11. file. The element content is a base64-encoded binary file
encoded as a BYTE[] type.

12. path. The element content is a file-system path encoded as a
STRING type.

13. frame. The element content is a Layer 2 frame encoded as a
HEXBIN type.

14. packet. The element content is a Layer 3 packet encoded as a
HEXBIN type.

15. ipv4-packet. The element content is an IPv4 packet encoded
as a HEXBIN type.

16. ipv6-packet. The element content is an IPv6 packet encoded
as a HEXBIN type.

18. csv. The element content is a comma-separated value (CSV)
list per Section 2 of [RFC4180] encoded as a STRING type.

19. winreg. The element content is a Microsoft Windows registry
key encoded as a STRING type.

21. monitoring-host. System activity (e.g., running processes,
keystrokes) were monitored.

22. policy. Activity violated the system owner's acceptable use
policy.

26. assessment. Assessment server (e.g., vulnerability scanner,
endpoint assessment).

40. scada. Supervisory control and data acquisition (SCADA)
system.

47. drop-server. Server to which exfiltrated content is
uploaded.