Network Working Group                                         T. Harding
Request for Comments: 4823                                      R. Scott
Category: Informational                                            Axway
                                                              April 2007

FTP Transport for Secure Peer-to-Peer
Business Data Interchange over the Internet

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

Copyright (C) The IETF Trust (2007).

Abstract

   This Applicability Statement (AS) describes how to exchange
   structured business data securely using the File Transfer Protocol
   (FTP) for XML, Binary, Electronic Data Interchange (EDI - ANSI X12 or
   UN/EDIFACT), or other data used for business-to-business data
   interchange for which MIME packaging can be accomplished using
   standard MIME content types.  Authentication and data confidentiality
   are obtained by using Cryptographic Message Syntax (S/MIME) security
   body parts.  Authenticated acknowledgements employ multipart/signed
   replies to the original message.

   1. Introduction ....................................................4
   2. Overview ........................................................4
      2.1. Overall Operations .........................................4
      2.2. Purpose of a Security Guideline for MIME EDI ...............5
      2.3. Definitions ................................................5
           2.3.1. Terms ...............................................5
           2.3.2. The Secure Transmission Loop ........................6
           2.3.3. Definition of Receipts ..............................7
      2.4. Operational Assumptions and Options ........................8
           2.4.1. EDI/EC Process Assumptions ..........................8
           2.4.2. Process Options .....................................8
                  2.4.2.1. Security Options ...........................8
                  2.4.2.2. Compression Options .......................10
   3. Referenced RFCs and Their Contribution .........................10
      3.1. RFC 959: File Transfer Protocol [3] .......................10
      3.2. RFC 2228: FTP Security Extensions [4] .....................10
      3.3. RFC 1847: MIME Security Multiparts [7] ....................10
      3.4. RFC 3462: Multipart/Report [12] ...........................11
      3.5. RFC 1767: EDI Content [2] .................................11
      3.6. RFCs 2045, 2046, and 2049: MIME [1] .......................11
      3.7. RFC 3798: Message Disposition Notification [6] ............11
      3.8. RFC 3852: CMS [9] and RFC 3851: S/MIME Version 3.1
           Message Specification [10] ................................11
      3.9. RFC 3850: S/MIME Version 3.1 Certificate Handling [11] ....11
      3.10. RFC 3274: Compressed Data Content Type for
            Cryptographic Message Syntax (CMS) [17] ..................11
      3.11. RFC 3023: XML Media Types [16] ...........................12
   4. Structure of an AS3 Message ....................................12
      4.1. Introduction ..............................................12
      4.2. Structure of an Internet EDI MIME Message .................12
   5. AS3-Specific Headers ...........................................13
      5.1. AS3-From and AS3-To Headers ...............................13
      5.2. AS3-Version Header ........................................14
   6. FTP Considerations .............................................15
      6.1. FTP Security Requirements .................................15
      6.2. Large File Transfers ......................................15
      6.3. MIME Considerations for FTP ...............................15
           6.3.1. Required/Optional Headers ..........................15
           6.3.2. Content-Transfer-Encoding ..........................16
           6.3.3. Epilogue Must Be Empty .............................16
           6.3.4. Message-Id and Original-Message-Id .................16
   7. Structure and Processing of an MDN Message .....................17
      7.1. Introduction ..............................................17
      7.2. Message Disposition Notifications (MDN) ...................19
      7.3. Requesting a Signed Receipt ...............................19
           7.3.1. Signed Receipt Considerations ......................22

      7.4. MDN Format and Value ......................................23
           7.4.1. AS3-MDN General Formats ............................23
           7.4.2. AS3-MDN Construction ...............................24
           7.4.3. AS3-MDN Fields .....................................25
           7.4.4. Additional AS3-MDN Programming Notes ...............26
      7.5. Disposition Mode, Type, and Modifier ......................29
           7.5.1. Disposition Mode Overview ..........................29
           7.5.2. Successful Processing Status Indication ............29
           7.5.3. Unsuccessful Processed Content .....................29
           7.5.4. Unsuccessful Non-Content Processing ................30
           7.5.5. Processing Warnings ................................31
   8. Public Key Certificate Handling ................................32
   9. Security Considerations ........................................33
   10. References ....................................................34
      10.1. Normative References .....................................34
      10.2. Informative References ...................................36
   Appendix A. Message Examples ......................................37
      A.1. Signed Message Requesting a Signed Receipt ................37
      A.2. MDN for Message A.1 Above .................................37

1. Introduction

   Previous work on Internet EDI focused on specifying MIME content
   types for EDI data [2] and extending this work to support secure
   EC/EDI transport over SMTP [5].  This document expands on RFC 1767 to
   specify a comprehensive set of data security features, specifically,
   data privacy, data integrity, authenticity, non-repudiation of
   origin, and non-repudiation of receipt over FTP.  This document also
   recognizes contemporary RFCs and is attempting to "re-invent" as
   little as possible.  While this document focuses on EDI data, any
   other data type describable in a MIME format is also supported.

   Internet MIME-based EDI can be accomplished by using and complying
   with the following documents:

         - RFC 959: File Transfer Protocol
         - RFC 2228: FTP Security Extensions
         - RFC 1767: EDI Content Type
         - RFC 3023: XML Media Types
         - RFC 1847: Security Multiparts for MIME
         - RFC 3462: Multipart/Report
         - RFCs 2045 to 2049: MIME
         - RFC 3798: Message Disposition Notification
         - RFCs 3850, 3851, and 3852: S/MIME v3.1 Specifications
         - RFC 3274: Compressed Data Content for Cryptographic Message
           Syntax
         - RFC 4217: Securing FTP with TLS
         - "Compressed Data for EDIINT" by T. Harding

   Our intent here is to define clearly and precisely how these are used
   together, and what is required by user agents to be compliant with
   this document.

   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 RFC 2119 [19].

2. Overview

2.1. Overall Operations

   An FTP upload operation is used to send appropriately packaged EDI,
   XML, or other business data.  The receiving application will poll the
   FTP server for inbound messages, unpackage and handle the message
   data, and generate a reply for the originator that contains a message
   disposition acknowledgement within a multipart/report that is signed
   or unsigned.  This request/reply transactional interchange provides
   secure, reliable, and authenticated transport for EDI or other

business data using FTP. The security protocols and structures used
also support auditable records of these transmissions.

2.2. Purpose of a Security Guideline for MIME EDI

   The purpose of these specifications is to ensure interoperability
   between B2B Electronic Commerce user agents, invoking some or all of
   the commonly expected security features.  This document is also NOT
   limited to strict EDI use, but applies to any electronic commerce
   application where business data needs to be exchanged over the
   Internet in a secure manner.

2.3. Definitions

2.3.1. Terms

   AS3                  Applicability Statement 3.  This is the third
                        applicability statement produced by the IETF
                        EDIINT working group.

   EDI                  Electronic Data Interchange

   EC                   Business-to-Business Electronic Commerce

   B2B                  Business to Business

   Receipt              The functional message that is sent from a
                        receiver to a sender to acknowledge receipt of
                        an EDI/EC interchange.

   Signed Receipt       A receipt containing a digital signature.

   Message Disposition  The Internet messaging format used to convey a
   Notification (MDN)   receipt.  This term is used interchangeably with
                        receipt.  An MDN is a receipt.

   Non-repudiation of NRR is a "legal event" that occurs when the
   receipt (NRR)        original sender of an EDI/EC interchange has
                        verified the signed receipt coming back from the
                        receiver.  NRR IS NOT a functional or a
                        technical message.

   S/MIME               A format and protocol for adding Cryptographic
                        signature and/or encryption services to Internet
                        MIME messages.

                        NOTE: While the S/MIME specification describes
                              more than one format for a signed message,
                              all signed messages or receipts used with
                              AS3 MUST utilize the multipart/signed
                              format.

   SHA-1                A secure, one-way hash algorithm used in
                        conjunction with digital signature.  SHA-1 is
                        the recommend algorithm for AS3.

   MD5                  A secure, one-way hash algorithm used in
                        conjunction with digital signature.  This
                        algorithm is acceptable but not recommended due
                        to its short key length and known weaknesses.

   MIC                  The message integrity check (MIC) is a
                        representation of the message digest, which
                        results from the application of the selected
                        hash algorithm to the content to be signed.  Of
                        particular interest is the digital signature,
                        which includes an encrypted copy of the digest.
                        Additionally, an MDN containing a Received-
                        content-MIC header will also contain (as that
                        header's value) a base-64-encoded representation
                        of the digest.

   User Agent (UA)      The application that handles and processes the
                        AS3 request.

   STL                  Secure Transmission Loop, described in the next
                        section.

2.3.2. The Secure Transmission Loop

   This document's focus is on the formats and protocols for exchanging
   EDI/EC content to which security services have been applied using the
   File Transmission Protocol (FTP) as the transport.

   The "Secure Transmission Loop" (STL) comprises the following two
   steps:

   a) The originator sends a signed and encrypted document with a
      request for a signed receipt.

   b) The recipient decrypts the document, verifies the signature, and
      returns a signed receipt to the sender.

   In other words, the following events occur during the execution of
   the STL:

   - The organization sending EDI/EC data signs and encrypts the data
     using S/MIME.  In addition, the message will request a signed
     receipt to be returned to the sender of the message.

   - The receiving organization decrypts the message and verifies the
     signature, resulting in verified integrity of the data and
     authenticity of the sender.

   - The receiving organization then returns a signed receipt, as
     requested to the sending organization in the form of a message
     disposition notification.  This signed receipt will contain the
     hash of the signature from the received message, indicating to the
     sender that the received message was verified and/or decrypted
     properly.

   The above describes functionality that, if implemented, will satisfy
   all security requirements and provide non-repudiation of receipt for
   the exchange.  While trading partners will usually want to utilize
   the STL, this specification does not require it.

2.3.3. Definition of Receipts

   The term used for both the functional activity and the message for
   acknowledging delivery of an EDI/EC interchange is "receipt" or
   "signed receipt".  The term receipt is used if the acknowledgment is
   for an interchange resulting in a receipt that is NOT signed.  The
   term signed receipt is used if the acknowledgment is for an
   interchange resulting in a receipt that IS signed.  A term often used
   in combination with receipts is non-repudiation of receipt.  NRR
   refers to a legal event that occurs only when the original sender of
   an interchange has verified the signed receipt coming back from the
   recipient of the message.  Note that NRR is not possible without
   signatures.

   For additional information on formatting and processing receipts in
   AS3, refer to Section 7.

2.4. Operational Assumptions and Options

2.4.1. EDI/EC Process Assumptions

   - Encrypted object is an EDI/EC Interchange.

     This specification assumes that a typical EDI/EC interchange is the
     lowest level object that will be subject to the application of
     security services.

     Specifically, for EDI ANSI X12, the entire document (including the
     ISA and IEA segments) is the atom to which security is applied.
     For EDIFACT, the corresponding definition includes the segments
     UNA/UNB and UNZ.  In other words, EDI/EC interchanges including
     envelope segments remain intact and unreadable during secure
     transport.

   - EDI envelope headers are encrypted.

     Congruent with the above statement, EDI envelope headers are NOT
     visible in the MIME package.  In order to optimize routing from
     existing commercial EDI networks (called Value Added Networks or
     VANs) to the Internet, work may need to be done in the future to
     define ways to extract some elements of the envelope to make them
     visible; however, that is beyond the scope of this specification.

   - X12.58 and UN/EDIFACT security considerations

     The most common EDI standards bodies, ANSI X12 and EDIFACT, have
     defined internal provisions for security.  X12.58 is the security
     mechanism for ANSI X12, and AUTACK provides security for EDIFACT.
     This specification DOES NOT dictate use or non-use of these
     security standards.  They are both fully compatible, though
     possibly redundant, with this specification.

2.4.2. Process Options

2.4.2.1. Security Options

   - Encrypted or un-encrypted data

     This specification allows for EDI/EC message exchange where the
     EDI/EC data can be either un-protected or protected by means of
     encryption.

   - Signed or unsigned data

     This specification allows for EDI/EC message exchange with or
     without digital signature of the original EDI transmission.

   - Use of receipt or not

     This specification allows for EDI/EC message transmission with or
     without a request for receipt notification.  If a signed receipt
     notification is requested, however, a MIC value is REQUIRED as part
     of the returned receipt, unless an error condition occurs that
     results in the inability to compute a valid digest.  (Such a case
     would result, for instance, if an encrypted message could not be
     decrypted.) Under such circumstances, an unsigned receipt (MDN)
     SHOULD be returned with the correct "disposition modifier" error
     value.

   - Security formatting

     This specification relies on the guidelines set forth in RFCs 3852
     [9] and 3851 [10].  The first of these RFCs describes the
     Cryptographic Message Syntax (CMS), and the second contains the
     S/MIME Version 3.1 Message Specification describing a MIME
     container for CMS objects.  Whenever the term S/MIME is used in
     this document, it refers to Version 3.1 as described therein.

   - Hash function, message digest choices

     When a signature is used, it is RECOMMENDED that the SHA-1 hash
     algorithm be used for all outgoing messages; however, both MD5 and
     SHA-1 MUST be supported for incoming messages.

   - Permutation summary

     In summary, the following twelve security permutations are possible
     in any given trading relationship:

     1.  Sender sends un-encrypted data, does NOT request a receipt.

     2.  Sender sends un-encrypted data, requests an unsigned receipt.
         The receiver sends back the unsigned receipt.

3. Sender sends un-encrypted data, requests a signed receipt. The
receiver sends back the signed receipt.

4. Sender sends encrypted data, does NOT request a receipt.

5. Sender sends encrypted data, requests an unsigned receipt. The
receiver sends back the unsigned receipt.

6. Sender sends encrypted data, requests a signed receipt. The
receiver sends back the signed receipt.

7. Sender sends signed data, does NOT request a receipt.

8. Sender sends signed data, requests an unsigned receipt.
Receiver sends back the unsigned receipt.

9. Sender sends signed data, requests a signed receipt. Receiver
sends back the signed receipt.

10. Sender sends encrypted and signed data, does NOT request a
receipt.

11. Sender sends encrypted and signed data, requests an unsigned
receipt. Receiver sends back the unsigned receipt.

     12. Sender sends encrypted and signed data, requests a signed
         receipt.  Receiver sends back the signed receipt.  This case
         represents the Secure Transmission Loop described above.

2.4.2.2. Compression Options

   The AS3 specification supports compression of transmitted data
   directly through the application of RFC 3274.  Implementation details
   may be found in that RFC and in Harding's document, "Compressed Data
   for EDIINT".

3.  Referenced RFCs and Their Contribution

3.1. RFC 959: File Transfer Protocol [3]

RFC 959 specifies how data is transferred using the File Transfer
Protocol (FTP)

3.2. RFC 2228: FTP Security Extensions [4]

This RFC describes a framework for providing security services to
FTP.

3.3. RFC 1847: MIME Security Multiparts [7]

This document defines security multiparts for MIME:
multipart/encrypted and multipart/signed.

3.4. RFC 3462: Multipart/Report [12]

RFC 3462 defines the use of the multipart/report content type, upon
which RFC 3798 builds to define the Message Disposition Notification.

3.5. RFC 1767: EDI Content [2]

   This RFC defines the use of content type "application" for ANSI X12
   (application/EDI-X12), EDIFACT (application/EDIFACT), and mutually
   defined EDI (application/EDI-Consent).

3.6. RFCs 2045, 2046, and 2049: MIME [1]

   These are the basic MIME standards, upon which all MIME-related RFCs
   build, including this one.  Key contributions include definitions of
   "content type", "sub-type", and "multipart", as well as encoding
   guidelines, which establish 7-bit US-ASCII as the canonical character
   set to be used in Internet messaging.

3.7. RFC 3798: Message Disposition Notification [6]

   This Internet RFC defines how a Message Disposition Notification
   (MDN)is requested, as well as the format and syntax of the MDN.  The
   MDN is the vehicle used by this specification to provide both signed
   and unsigned receipts.

3.8. RFC 3852: CMS [9] and RFC 3851: S/MIME Version 3.1 Message
Specification [10]

This specification describes how MIME shall carry Cryptographic
Message Syntax (CMS) Objects.

3.9. RFC 3850: S/MIME Version 3.1 Certificate Handling [11]

RFC 3850 describes certificate handling in the context of CMS and
S/MIME.

3.10. RFC 3274: Compressed Data Content Type for Cryptographic Message
Syntax (CMS) [17]

This specification provides a mechanism to wrap compressed data
within a CMS object.

3.11. RFC 3023: XML Media Types [16]

   This RFC defines the use of content type "application" for XML.  Note
   that while conforming implementations SHOULD support the expanded
   syntax that RFC 3023 introduces for the "+xml" suffix, no support for
   external parsed entity types is anticipated (as it adds significant
   complexity to signature processing).

4.  Structure of an AS3 Message

4.1. Introduction

   The basic structure of AS3 messages comprises MIME encapsulated data
   with both customary MIME headers and a few additional AS3-specific
   outer headers.  The structures below are described hierarchically in
   terms of which RFCs have been applied to form the specific structure.
   The reader is referred directly to the referenced RFCs for
   implementation details.

   Any additional restrictions imposed by this AS are specifically
   discussed in the sections that follow.

4.2. Structure of an Internet EDI MIME Message

   No encryption, no signature

     -RFC822/2045
       -RFC1767/RFC2376 (application/EDIxxxx or /xml)

   No encryption, signature

     -RFC822/2045
       -RFC1847 (multipart/signed)
         -RFC1767/RFC2376 (application/EDIxxxx or /xml)
         -RFC3851 (application/pkcs7-signature)

   Encryption, no signature

     -RFC822/2045
       -RFC3851 (application/pkcs7-mime)
         -RFC1767/RFC2376  (application/EDIxxxx or /xml)(encrypted)

   Encryption, signature

     -RFC822/2045
       -RFC3851 (application/pkcs7-mime)
         -RFC1847 (multipart/signed)(encrypted)
           -RFC1767/RFC2376  (application/EDIxxxx or /xml)(encrypted)
           -RFC3851 (application/pkcs7-signature)(encrypted)

   MDN, no signature

     -RFC822/2045
       -RFC3798 (message/disposition-notification)

   MDN, signature

     -RFC822/2045
       -RFC1847 (multipart/signed)
         -RFC3798 (message/disposition-notification)
         -RFC3851 (application/pkcs7-signature)

   While all MIME content types SHOULD be supported,
   the following MIME content types MUST be supported:

     Content-Type: multipart/signed
     Content-Type: multipart/report
     Content-type: message/disposition-notification
     Content-Type: application/PKCS7-signature
     Content-Type: application/PKCS7-mime
     Content-Type: application/EDI-X12
     Content-Type: application/EDIFACT
     Content-Type: application/edi-consent
     Content-Type: application/XML

5.  AS3-Specific Headers

5.1. AS3-From and AS3-To Headers

   The AS3-From and AS3-To headers have been provided to assist the
   sender and the recipient of an EC document to identify each other:

      AS3-From: < AS3-name >
      AS3-To:   < AS3-name >

   These headers contain textual values, described by the ABNF [22]
   below, identifying the sender/receiver of a data exchange.  A value
   may be company specific (e.g., a Data Universal Numbering System
   (DUNS) number), or it may be simply some string mutually acceptable
   to both trading partners used to identify each to the other.

    AS3-text = "!" /           ; printable ASCII characters
               %d35-91 /       ; except double-quote (%d34)
               %d93-126        ; or backslash (%d92)

    AS3-qtext = AS3-text / SP  ; allow space only in quoted text

    AS3-quoted-pair = "\" DQUOTE /  ; \" or
                      "\" "\"       ; \\

    AS3-quoted-name = DQUOTE 1*128( AS3-qtext /
                      AS3-quoted-pair) DQUOTE

    AS3-atomic-name = 1*128AS3-text

    AS3-name = AS3-atomic-name / AS3-quoted-name

    Note: SP and DQUOTE are defined in [ABNF]RFC 4234.

   The AS3-From header value and the AS3-To header value MUST each be an
   AS3-name comprising 1 to 128 printable ASCII characters.  The header
   MUST NOT be folded, and the value for each of these headers is case-
   sensitive.

   The AS3-quoted-name SHOULD be used only if the AS3-name does not
   conform to AS3-atomic-name.

   The AS3-To and AS3-From header fields MUST be present in all AS3
   messages and AS3 MDNs.

   Implementations that map entities such as EDI identifiers/qualifiers
   to AS3 identifiers may choose to constrain the set of AS3-To/AS3-From
   text values to a subset of the full set defined above, but they may
   not extend that set.

   If the AS3-From or the AS3-To or the association of the two header
   values is determined to be invalid or unknown to the receiving
   system, the receiving system MAY respond with an unsigned MDN
   containing an explanation of the error if the sending system
   requested an MDN, but it is not required to return an MDN under those
   circumstances.

5.2. AS3-Version Header

   The AS3-Version header is a header that is required only if the value
   of the header is not "1.0".  Its purpose is to allow systems to
   determine which version of this specification (should the
   specification evolve over time) the sender of a document has used to

   package the document.  A user agent MUST NOT reject a message if the
   version header is missing.

   AS3-Version: 1*DIGIT . 1*DIGIT

   A version header value of "1.1" indicates an implementation can
   support EDIINT data compression [20].  A user agent MUST NOT send
   compressed messages to trading partners who do not use a version
   header of "1.1" or greater.

6.  FTP Considerations

6.1. FTP Security Requirements

   FTP has long been viewed as an insecure protocol primarily because of
   its use of cleartext authentication [3].  This is addressed by RFC
   2228 [4], and the use of one of the security mechanisms described
   therein is strongly encouraged.  Specifically, conforming
   implementations of AS3 SHALL employ FTP client/servers that support
   the AUTH command described within [4].  While any authentication
   mechanism based upon [4] MAY be utilized, AUTH TLS (as described in
   [18]) MUST be supported. (Note that [18] relies on TLS Version 1.0
   [13], not Version 1.1 [23].)

6.2. Large File Transfers

   Large files are handled correctly by the TCP layer.  However, the
   mechanism for compressing data, referenced in Section 2.4.2.2,
   efficiently reduces transmission requirements for many data types
   (including both XML and traditional EDI data).  Additionally, some
   FTP implementations support compression as well.

6.3. MIME Considerations for FTP

6.3.1. Required/Optional Headers

   An AS3 message MUST contain the following outer headers:

        AS3-To
        AS3-From
        Date
        Message-ID
        Content-Type

   An AS3 message OPTIONALLY MAY contain the following outer headers:

        Subject
        AS3-Version (assumed to be 1.0 if not present)
        Content-Length

   An AS3 message requesting a receipt MUST contain a Disposition-
   Notification-To header and MAY contain a Disposition-Notification-
   Options header (if the receipt is to be signed).

   Additional headers MAY be present but are ignored.

6.3.2. Content-Transfer-Encoding

   FTP defines several data structures and character encodings via the
   STRU[cture] and TYPE commands.  AS3 requires the file-structure
   (default) and the image type.  The Content-Transfer-Encoding header
   SHOULD NOT be used; if the header is present, it SHOULD have a value
   of binary or 8-bit.  The absence of this header or the use of
   alternate values such as "base64" or "quoted-printable" MUST NOT
   result in transaction failure.  Content transfer encoding of MIME
   parts within the AS3 message are similarly constrained.

6.3.3. Epilogue Must Be Empty

A MIME message containing an epilogue [1] SHALL NOT be used.

6.3.4. Message-Id and Original-Message-Id

   Message-Id and Original-Message-Id are formatted as defined in
   Section 3.6.4 of RFC 2822 [15]: "<" id-left "@" id-right ">".
   Message-Id length is a maximum of 998 characters.  Message-Id SHOULD
   be globally unique; id-right should be something unique to the
   sending host environment (e.g., a host name).  When sending a
   message, always include the angle brackets.  Angle brackets are not
   part of the Message-Id value.

   NOTE: When creating the Original-Message-Id header in an MDN, always
         use the exact syntax contained in the original message: do not
         strip or add "angle brackets".

7. Structure and Processing of an MDN Message

7.1. Introduction

   In order to support non-repudiation of receipt, a signed receipt,
   based on digitally signing a message disposition notification, is to
   be implemented by a receiving trading partner's UA.  The message
   disposition notification specified by RFC 3798 is digitally signed by
   a receiving trading partner as part of a multipart/signed MIME
   message.

   The following support for signed receipts is REQUIRED:

   1) The ability to create a multipart/report; where the report-type =
      disposition-notification.

   2) The ability to calculate a message integrity check (MIC) on the
      received message.  The calculated MIC value will be returned to
      the sender of the message inside the signed receipt.

   3) The ability to create a multipart/signed content with the message
      disposition notification as the first body part, and the signature
      as the second body part.

   4) The ability to return the signed receipt to the sending trading
      partner.

   The signed receipt is used to notify a sending trading partner that
   requested the signed receipt that:

   1) The receiving trading partner acknowledges receipt of the sent EC
      Interchange.

   2) If the sent message was signed, then the receiving trading partner
      has authenticated the sender of the EC Interchange.

   3) If the sent message was signed, then the receiving trading partner
      has verified the integrity of the sent EC Interchange.

   Regardless of whether the EDI/EC Interchange was sent in S/MIME
   format or not, the receiving trading partner's UA MUST provide the
   following basic processing:

   1) If the sent EDI/EC Interchange is encrypted, then the encrypted
      symmetric key, and initialization vector (if applicable) is
      decrypted using the receiver's private key.

   2) The decrypted symmetric encryption key is then used to decrypt the
      EDI/EC Interchange.

   3) The receiving trading partner authenticates signatures in a
      message using the sender's public key.

      The authentication algorithm performs the following:

      a) The message integrity check (MIC or Message Digest) is
         decrypted using the sender's public key.

      b) A MIC on the signed contents (the MIME header and encoded EDI
         object, as per RFC 1767) in the message received is calculated
         using the same one-way hash function that the sending trading
         partner used.

      c) The MIC extracted from the message that was sent and the MIC
         calculated using the same one-way hash function that the
         sending trading partner used are compared for equality.

   4) The receiving trading partner formats the MDN and sets the
      calculated MIC into the "Received-content-MIC" extension field.

   5) The receiving trading partner creates a multipart/signed MIME
      message according to RFC 1847.

   6) The MDN is the first part of the multipart/signed message, and the
      digital signature is created over this MDN, including its MIME
      headers.

   7) The second part of the multipart/signed message contains the
      digital signature.  The "protocol" option specified in the second
      part of the multipart/signed is as follows: S/MIME: protocol =
      "application/pkcs7-signature".

   8) The signature information is formatted according to S/MIME
      specifications.  The EC Interchange and the RFC 1767 MIME EDI
      content header can actually be part of a multipart MIME content
      type.  When the EDI Interchange is part of a multipart MIME
      content type, the MIC MUST be calculated across the entire
      multipart content, including the MIME headers.

   The signed MDN, when received by the sender of the EDI Interchange
   can be used by the sender:

   1) As an acknowledgment that the EDI Interchange was sent, and then
      was delivered and acknowledged by the receiving trading partner.

      The receiver does this by returning the original-message-id of the
      sent message in the MDN portion of the signed receipt.

   2) As an acknowledgment that the integrity of the EDI Interchange was
      verified by the receiving trading partner.  The receiver does this
      by returning the calculated MIC of the received EC Interchange
      (and 1767 MIME headers) in the "Received-content-MIC" field of the
      signed MDN.

   3) As an acknowledgment that the receiving trading partner has
      authenticated the sender of the EDI Interchange.

   4) As a non-repudiation of receipt when the signed MDN is
      successfully verified by the sender with the receiving trading
      partner's public key and the returned MIC value inside the MDN is
      the same as the digest of the original message.

7.2. Message Disposition Notifications (MDN)

   The AS3-MDNs are returned on a separate FTP TCP/IP connection and are
   a response to an AS3 message.

   The following diagram illustrates the delivery of an AS3-MDN
   delivery:

          AS3-MDN
         [S] ----( connect )----> [R]   [FTP Server]
         [S] ----( send )-------> [R]   [AS3-Message]
         [S] ----( disconnect )-> [R]   [FTP Server]

         [S] <---( connect )----- [R]   [FTP Server]
         [S] <---( send )-------- [R]   [AS3-MDN]]
         [S] <---( disconnect )-- [R]   [FTP Server]

         Note: Refer to Section 7.4.4 for additional
               programming notes.

7.3. Requesting a Signed Receipt

   Message Disposition Notifications are requested as per RFC 3798.  A
   request that the receiving user agent issue a message disposition
   notification is made by placing the following header into the message
   to be sent:

   MDN-request-header = "Disposition-notification-to" ":" ftpurl

   This syntax is a residual of the use of MDN's in an SMTP transfer.
   Since this specification is adjusting the functionality from SMTP to

   FTP and retaining as much as possible from the [5] functionality, the
   ftpurl must be present.

   The ftpurl field is specified as an RFC 1738 <URL:"ftp://" login [
   "/" fpath [ ";type=" ftptype ]]>, and while it MUST be present, it
   may be ignored if the ftpurl points to an unknown location.  If the
   ftpurl points to an unknown location, it is RECOMMENDED that the mdn
   is returned back to a known ftpurl for the sender of the received
   message.

   For requesting MDN-based receipts, the originator supplies the
   required extension headers that precede the message body.

   The header "tags" are as follows:

   A Disposition-notification-to header is added to indicate that a
   message disposition notification is requested.  This header is
   specified in [6].

   A Message-ID header is added to support message reconciliation, so
   that an Original-Message-Id value can be returned in the body part of
   the MDN.

   Other headers, especially "Date", SHOULD be supplied; the values of
   these headers are often mentioned in the human-readable section of an
   MDN to aid in identifying the original message.

   Disposition-notification-options identifies characteristics of the
   message.

   The following Disposition notification is in accordance with [6].

       EXAMPLE:
         Disposition-notification-to:       // Requests the MDN
           ftp://host:port/inbox            // Location to return MDN
         Disposition-notification-options:  // The signing options for
                                               MDN
           signed-receipt-protocol=optional, pkcs7-signature;
           signed-receipt-micalg=optional, sha1, md5

   Disposition-notification-options syntax:

   Disposition-notification-options =
          "Disposition-Notification-Options:"
           disposition-notification-parameters

   disposition-notification-parameters =
               parameter *(";" parameter)

   parameter = attribute "=" importance ", " value *("," value)

   importance = "required" / "optional"

   attribute = "signed-receipt-protocol" / "signed-receipt-micalg"

   So the Disposition-notification-options string could be:

     signed-receipt-protocol=optional, <protocol symbol>;
     signed-receipt-micalg=optional, <micalg1>, <micalg2>,...;

   The currently supported value for <protocol symbol> is "pkcs7-
   signature" for the S/MIME detached signature format.

   The currently supported values for MIC algorithm <micalg> values are:

          Algorithm   Value
           Used
        --------   -------
           MD5         md5
           SHA-1       sha1

   Receiving agents SHOULD be able to recover gracefully from a <micalg>
   parameter value that they do not recognize.

   The semantics of the "signed-receipt-protocol" parameter is as
   follows:

   1) The "signed-receipt-protocol" parameter is used to request a
      signed receipt from the recipient trading partner.  The "signed-
      receipt-protocol" parameter also specifies the format in which the
      signed receipt should be returned to the requester.

      The "signed-receipt-micalg" parameter is a list of MIC algorithms
      preferred by the requester for use in signing the returned receipt
      and calculating the micalg in the Received-content-MIC header.

      The list of MIC algorithms should be honored by the recipient from
      left to right.  Both the "signed-receipt-protocol" and the
      "signed-receipt-micalg" option parameters are REQUIRED when
      requesting a signed receipt.

   2) The "importance" attribute of "Optional" is defined in RFC 3798,
      Section 2.2, and has the following meaning:

      Parameters with an importance of "Optional" permit a UA that does
      not understand the particular options parameter to still generate
      an MDN in response to a request for an MDN.  A UA that does not

      understand the "signed-receipt-protocol" parameter, or the
      "signed-receipt-micalg" parameter, will obviously not return a
      signed receipt.

      The importance of "Optional" is used for the signed receipt
      parameters because it is RECOMMENDED that an MDN be returned to
      the requesting trading partner even if the recipient could not
      sign it.

      The returned MDN will contain information on the disposition of
      the message as well as on why the MDN could not be signed.  See
      the Disposition field in Section 7.5 for more information.

   Within an EDI trading relationship, if a signed receipt is expected
   and is not returned, then the validity of the transaction must be
   determined by the trading partners.  Typically, if a signed receipt
   is required by the trading relationship and is not received, the
   transaction will likely not be considered valid.

7.3.1. Signed Receipt Considerations

   The method used to request a receipt or a signed receipt is defined
   in RFC 3798, "An Extensible Message Format for Message Disposition
   Notifications".

   The "rules" for processing a receipt-request follow:

   1) When a receipt is requested, explicitly specifying that the
      receipt be signed, then the receipt MUST be returned with a
      signature unless conditions (2) or (3) below are applicable.

   2) When a receipt is requested, explicitly specifying that the
      receipt be signed, but the recipient cannot support either the
      requested protocol format, or requested MIC algorithms, then
      either a signed or unsigned receipt SHOULD be returned.

   3) When a receipt is requested, explicitly specifying that the
      receipt be signed, but the recipient is unable to compute the
      digest (e.g., message was encrypted, and recipient unable to
      decrypt), then the recipient SHOULD NOT return "Received-content-
      MIC" in the MDN to the requestor.  If the MDN sets the disposition
      (e.g., "processed/error: decryption-failed") appropriately, then
      the "Received-content-MIC" may be returned, but the value must be
      discarded.

   4) When a signature is not explicitly requested, or if the signed
      receipt request parameter is not recognized by the UA, then no
      receipt, an unsigned receipt, or a signed receipt MAY be returned
      by the recipient.

   5) If a message is received without a request for a receipt, then a
      receipt (signed or unsigned) MAY be returned.

      The "Received-content-MIC" MUST be calculated as follows:

      - For any signed messages, the MIC to be returned is calculated on
        the RFC 1767 MIME header and content.  Canonicalization as
        specified in RFC 1848 MUST be performed before the MIC is
        calculated, since the sender requesting the signed receipt was
        also REQUIRED to canonicalize.

      - For encrypted, unsigned messages, the MIC to be returned is
        calculated on the decrypted RFC 1767 MIME header and content.
        The content after decryption MUST be canonicalized before the
        MIC is calculated.

      - For unsigned, un-encrypted messages, the MIC MUST be calculated
        over the message contents prior to Content-Transfer-Encoding and
        without the MIME or any other RFC 822 [14] headers, since these
        are sometimes altered or reordered by message transfer agents
        (MTAs).

7.4. MDN Format and Value

This section defines the format of the AS3 Message Disposition
Notification (AS3-MDN).

7.4.1. AS3-MDN General Formats

   The AS3-MDN follows the MDN specification [6] except where noted in
   this section.  The modified entity definitions in this document use
   the vertical-bar character, '|', to denote a logical "OR"
   construction.  Refer to RFC 2045 for the format of MIME-message-
   headers.

     The format of the AS3-MDN is

     MDN, no signature

       -RFC822/2045
         -RFC3798 (message/disposition-notification)

     MDN, signature

       -RFC822/2045
         -RFC1847 (multipart/signed)
           -RFC3798 (message/disposition-notification)
           -RFC3851 (application/pkcs7-signature)

7.4.2. AS3-MDN Construction

   The AS3-MDN-body is formatted as a MIME multipart/report with a
   report-type of "disposition-notification".

   When unsigned, the transfer-layer ("outermost") entity-headers of the
   AS3-MDN contain the Content-Type header that specifies a content type
   of "multipart/report", parameters indicating the report-type, and the
   value of the outermost multipart boundary.

   When the AS3-MDN is signed, the transfer-layer ("outermost") entity-
   headers of the AS3-MDN contain a Content-Type header that specifies a
   content type of "multipart/signed", parameters indicating the
   algorithm used to compute the message digest, the signature
   formatting protocol (e.g., pkcs7-signature), and the value of the
   outermost multipart boundary.  The first part of the MIME
   multipart/signed message is an imbedded MIME multipart/report of type
   "disposition-notification".  The second part of the multipart/signed
   message contains a MIME application/pkcs7-signature message.

   The first part of the MIME multipart/report is a "human-readable"
   portion that contains a general description of the message
   disposition.  The second part of the MIME multipart/report is a
   "machine-readable" portion that is defined as

     AS3-disposition-notification-content =
               [ reporting-ua-field CRLF ]
               [ mdn-gateway-field CRLF ]
               [ original-recipient-field CRLF ]
               final-recipient-field CRLF
               [ original-message-id-field CRLF ]
               AS3-disposition-field CRLF
               *( failure-field CRLF )
               *( error-field CRLF )
               *( warning-field CRLF )
               *( extension-field CRLF )
               [ AS3-received-content-MIC-field CRLF ]

   It is noted that several of the optional fields defined by RFC 3798
   and shown above are not relevant to a point-to-point transport such
   as FTP and would not normally appear in an AS3 MDN.

7.4.3. AS3-MDN Fields

   The rules for constructing the AS3-disposition-notification-content
   are identical to the rules for constructing the disposition-
   notification-content as defined in Section 7 of RFC 3798 [6] except
   that the RFC 3798 disposition-field has been replaced with the AS3-
   disposition-field and that the AS3-received-content-MIC field has
   been added.  The differences between the RFC 3798 disposition-field
   and the AS3-disposition-field are described below.  Where there are
   differences between this document and RFC 3798, those entity names
   have been changed by prepending "AS3-".  Entities below that do not
   differ from RFC 3798 are not necessarily further defined in this
   document.

   Refer to RFC 3798 [6] and RFC 4234 [22] for entities that are not
   further defined in this document.

     AS3-disposition-field = "Disposition:" disposition-mode ";"
                    AS3-disposition-type [ "/" AS3-disposition-modifier]

     disposition-mode = action-mode "/" sending-mode

     action-mode = "manual-action" / "automatic-action"

     sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"

     AS3-disposition-type = "processed" / "failed"

     AS3-disposition-modifier = ( "error" / "warning" ) /
                                AS3-disposition-modifier-extension

     AS3-disposition-modifier-extension =
                "error: authentication-failed" /
                "error: decompression-failed" /
                "error: decryption-failed" /
                "error: insufficient-message-security" /
                "error: integrity-check-failed" /
                "error: unexpected-processing-error" /
                "warning: " AS3-MDN-warning-description /
                "failure: " AS3-MDN-failure-description

     AS3-MDN-warning-description = *( TEXT )

     AS3-MDN-failure-description = *( TEXT )

     AS3-received-content-MIC-field =
                 "Received-content-MIC:" encoded-message-digest
                 "," digest-alg-id CRLF

     encoded-message-digest =
                1*( ALPHA / DIGIT / "/" / "+" ) *3"="
                ;( i.e. base64( message-digest ) )

     digest-alg-id = "sha1" / "md5"

   The "Received-content-MIC" extension field is set after the integrity
   of the received message is verified.  The MIC is the base64-encoded
   message-digest computed over the received message with a hash
   function.  This field is required for signed receipts but optional
   for unsigned receipts.  For details defining the specific content
   over which the message-digest is to be computed, see Section 7.3.1 of
   this document.

   The algorithm used to calculate the message digest MUST be the same
   as the "micalg" value used by the sender in the multipart/signed
   message.  When no signature is received, the message-digest MUST be
   calculated using the algorithm specified by the "micalg" value in the
   Disposition-Notification-Options header.  When no signature is
   received and no micalg parameter is provided, then the SHA-1
   algorithm MUST be used to calculate the digest.  This field is set
   only when the contents of the message are processed successfully.
   This field is used in conjunction with the recipient's signature on
   the MDN in order for the sender to verify non-repudiation of receipt.

   AS3-MDN field names (e.g., "Disposition:", "Final-Recipient:") are
   case-insensitive (cf. RFC 3798, Section 3.1.1).

   AS3-MDN action-modes, sending-modes, AS3-disposition-types, and AS3-
   disposition-modifier values that are defined above, and user-supplied
   *( TEXT ) values are also case-insensitive.  AS3 implementations MUST
   NOT make assumptions regarding the values supplied for AS3-MDN-
   warning-description or AS3-MDN-failure-description or for the values
   of any (optional) error, warning, or failure fields.

7.4.4. Additional AS3-MDN Programming Notes

   1.  Unlike SMTP, for FTP transactions, Original-Recipient and Final
       Recipient SHOULD NOT be different.  The value in Original-
       Message-ID MUST match the original Message-ID header value.

   2.  Refer to RFC 3462 and RFC 3798 for the formatting of the
       Content-Type entity-headers for the MDN.

   3.  Use an action-mode of "automatic-action" when the disposition
       described by the disposition type was a result of an automatic
       action, rather than an explicit instruction by the user for this
       message.

   4.  Use an action-mode of "manual-action" when the disposition
       described by the disposition type was a result of an explicit
       instruction by the user rather than some sort of automatically
       performed action.

   5.  Use a sending-mode of "MDN-sent-automatically" when the MDN is
       sent because the UA had previously been configured to do so.

   6.  Use a sending-mode of "MDN-sent-manually" when the user
       explicitly gave permission for this particular MDN to be sent.

   7.  The sending-mode "MDN-sent-manually" is ONLY meaningful with
       "manual-action", not with "automatic-action".

   8.  The "failed" disposition type MAY NOT be used for the situation
       in which there is some problem in processing the message other
       than interpreting the request for an MDN.  The "processed" or
       other disposition type with appropriate disposition modifiers is
       to be used in such situations.

   9.  An AS3 implementation MUST present to its trading partners an
       FTP-compliant server interface where inbound documents and MDNs
       are received.

   10. An AS3 implementation MUST be able to retrieve inbound messages
       from its currently configured FTP server interface.

   Note: Programming Notes 9 and 10 do not imply any specific method for
         supplying the FTP server interface.  But, they do allow for
         several different types of implementations.  Some vendors may
         choose to imbed an FTP-compliant server interface within their
         product, and others may choose to utilize off-the-shelf FTP
         servers to supply the required FTP server interface.  Some may
         choose to utilize hosting services provided by their trading
         partner or by a third-party hosting service.  Whichever method
         is utilized, an AS3 implementation MUST support rules 9 and 10.

   11. AS3 implementations MAY imbed an FTP server interface within
       their product.

12. AS3 implementations MUST be configurable to allow the use of an
external FTP hosting service.

Note: An external FTP hosting service may be hosted by a third-party
or possibly hosted by your trading partner.

   13. An AS3 implementation MUST be able to send business documents and
       MDNs to a trading partner's currently configured FTP server
       interface.

14. An AS3 implementation may imbed FTP client code into their
product or use a third-party FTP client.

15. Example Configurations

       1. Peer to Peer
          Trading Partner A (TPA) is using a local FTP server, and
          Trading Partner B (TPB) is using an imbedded FTP server.

       [A Client] ----( connect )----> [B Server]
       [A Client] ----( send )-------> [B Server] [AS3-Message]
       [A Client] ----( disconnect )-> [B Server]

       [A Server] <---( connect )----- [B Client]
       [A Server] <---( send )-------- [B Client] [AS3-MDN]]
       [A Server] <---( disconnect )-- [B Server]
       [A Client] <---( GET )--------- [A Server]

       2. Third-Party Hosting
          Both parties are using the same third-party-hosted FTP server.

       [A Client] ----( connect )----> [Hosted Server]
       [A Client] ----( send )-------> [Hosted Server] [AS3-Message]
       [A Client] ----( disconnect )-> [Hosted Server]
       [Hosted Server]( GET )--------> [B Client]

       [Hosted Server] <---( connect )----- [B Client]
       [Hosted Server] <---( send )-------- [B Client] [AS3-MDN]]
       [Hosted Server] <---( disconnect )-- [B Client]
       [A Client]      <---( GET )--------- [Hosted Server]

       3. Trading Partner Hosting
          TPA is using the imbedded FTP server hosted by TPB.

       [A Client] ----( connect )----> [B Server]
       [A Client] ----( send )-------> [B Server] [AS3-Message]
       [A Client] ----( disconnect )-> [B Server]

       [B Server] <---( connect )----- [B Client]
       [B Server] <---( send )-------- [B Client] [AS3-MDN]]
       [B Server] <---( disconnect )-- [B Client]
       [A Client] <---( GET )--------- [B Server]

7.5. Disposition Mode, Type, and Modifier

7.5.1. Disposition Mode Overview

This section will provide a brief overview of how processed, error,
failure, or warning notifications are used.

7.5.2. Successful Processing Status Indication

   When a receipt or signed receipt is requested, and the received
   message contents are successfully processed by the receiving EDI UA,
   a receipt or MDN SHOULD be returned with the "disposition-type" set
   to "processed".  When the MDN is sent automatically by the EDI UA,
   and there is no explicit way for a user to control the sending of the
   MDN, then the first part of the "disposition-mode" should be set to
   "automatic-action".

   When the MDN is being sent under user-configurable control, then the
   first part of the "disposition-mode" should be set to "manual-
   action".  Since a request for a signed receipt should always be
   honored, the user MUST not be allowed to configure the UA not to send
   a signed receipt when the sender requests one.

   The second part of the "disposition-mode" is set to "MDN-sent-
   manually" if the user gave explicit permission for the MDN to be
   sent.  Again, the user MUST not be allowed to explicitly refuse to
   send a signed receipt when the sender requests one.  The second part
   of the "disposition-mode" is set to "MDN-sent-automatically" whenever
   the EDI UA sends the MDN automatically, regardless of whether the
   sending was under a user's, an administrator's, or software control.

   Since EDI content is generally handled automatically by the EDI UA, a
   request for a receipt or signed receipt will generally return the
   following in the "disposition-field":

   Disposition: automatic-action/MDN-sent-automatically; processed

   Note this specification does not restrict the use of the
   "disposition-mode" to just automatic actions.  Manual actions are
   valid as long as it is kept in mind that a request for a signed
   receipt MUST be honored.

7.5.3. Unsuccessful Processed Content

   The request for a signed receipt requires the use of two
   "disposition-notification-options", which specify the protocol format
   of the returned signed receipt, and the MIC algorithm used to
   calculate the MIC over the message contents.  The "disposition-field"

   values that should be used in the case where the message content is
   being rejected or ignored should be specified in the MDN
   "disposition-field" as below.  (An example of this case is when the
   EDI UA determines that a signed receipt cannot be returned because it
   does not support the requested protocol format, so the EDI UA chooses
   not to process the message contents itself.)

   Disposition: "disposition-mode"; failed/Failure: unsupported Format

   The "failed" AS3-disposition-type should be used when a failure
   occurs that prevents the proper generation of an MDN.

   For example, this disposition-type would apply if the sender of the
   message requested the application of an unsupported message-
   integrity-check (MIC) algorithm.

   The "failure:" AS3-disposition-modifier-extension should be used with
   an implementation-defined description of the failure.

   Further information about the failure may be contained in a failure-
   field.  The syntax of the "failed" "disposition-type" is general,
   allowing the sending of any textual information along with the
   "failed"  "disposition-type".  Implementations WILL support any
   printable textual characters after the Failure disposition-type.

   For use in Internet EDI, the following "failed" values are pre-
   defined and MUST be supported:

        "Failure: unsupported format"
        "Failure: unsupported MIC-algorithms"

7.5.4. Unsuccessful Non-Content Processing

   When errors occur in processing the received message, other than
   content, the "disposition-field" should be set to the "processed"
   "disposition-type" value and the "error" "disposition-modifier"
   value.

   The "error" AS3-disposition-modifier with the "processed"
   disposition-type should be used to indicate that an error of some
   sort occurred that prevented successful processing of the message.

   Further information may be contained in an error-field.

   An "error:" AS3-disposition-modifier-extension should be used to
   combine the indication of an error with a pre-defined description of
   a specific, well-known error.  Further information about the error
   may be contained in an error-field.

   For use in Internet EDI, the following "error" "disposition-modifier"
   values are defined:

   "Error: decryption-failed"
      The receiver could not decrypt the message contents.

   "Error: authentication-failed"
      The receiver could not authenticate the sender.

   "Error: integrity-check-failed"
      The receiver could not verify content integrity.

   "Error: insufficient-message-security"
      The security level of the message did not match the agreed level
      between TPs.

   "Error: decompression-failed"
      The receiver could not decompress the message contents.

   "Error: unexpected-processing-error"
      A catch-all for any additional processing errors.

   An example of how the "disposition-field" would look when processing
   errors, other than content, are detected is as follows:

   EXAMPLE
        Disposition: "disposition-mode";
          processed/Error: decryption-failed

7.5.5. Processing Warnings

   Situations arise in EDI where even if a trading partner cannot be
   authenticated correctly, the trading partners still agree to continue
   processing the EDI transactions.  Transaction reconciliation is done
   between the trading partners at a later time.  In the content
   processing warning situations described above, the "disposition-
   field" SHOULD be set to the "processed" "disposition-type" value, and
   the "warning" "disposition-modifier" value.

   The "warning" AS3-disposition-modifier should be used with the
   "processed" disposition-type to indicate that the message was
   successfully processed but that an exceptional condition occurred.

   Further information may be contained in a warning-field.

   A "warning:" AS3-disposition-modifier-extension should be used to
   combine the indication of a warning with an implementation-defined
   description of the warning.  Further information about the warning
   may be contained in a warning-field.

   For use in Internet EDI, the following "warning" "disposition-
   modifier" values are defined:

   "Warning: authentication-failed, processing continued"

   An example of how the "disposition-field" would look when processing
   warnings, other than content, are detected is as follows:

   EXAMPLE
       Disposition: "disposition-mode"; processed/Warning:
         authentication-failed, processing continued

8.  Public Key Certificate Handling

   In the near term, the exchange of public keys and certification of
   these keys must be handled as part of the process of establishing a
   trading partnership.  The UA and/or EDI application interface must
   maintain a database of public keys used for encryption or signatures,
   in addition to the mapping between EDI trading partner ID and FTP
   URL/URI.  The procedures for establishing a trading partnership and
   configuring the secure EDI messaging system might vary among trading
   partners and software packages.

   X.509 certificates are REQUIRED.  It is RECOMMENDED that trading
   partners self-certify each other if an agreed-upon certification
   authority is not used.  This applicability statement does NOT require
   the use of a certification authority.

   The use of a certification authority is therefore OPTIONAL.
   Certificates may be self-signed.  It is RECOMMENDED that when trading
   partners are using S/MIME, that they also exchange public key
   certificates using the recommendations specified in the S/MIME
   Version 3.1 Message Specification.

   The message formats and S/MIME conformance requirements for
   certificate exchange are specified in this document.  In the long
   term, additional Internet-EDI standards may be developed to simplify
   the process of establishing a trading partnership, including the
   third-party authentication of trading partners, as well as attributes
   of the trading relationship.

9.  Security Considerations

   This entire document is concerned with secure transport of business-
   to-business data, and it considers both privacy and authentication
   issues.

   Extracted from S/MIME Version 2 Message Specification [21]:

      40-bit encryption is considered weak by most cryptographers.
      Using weak cryptography in S/MIME offers little actual security
      over sending plaintext.  However, other features of S/MIME, such
      as the specification of tripleDES and the ability to announce
      stronger cryptographic capabilities to parties with whom you
      communicate, allow senders to create messages that use strong
      encryption.  Using weak cryptography is never recommended unless
      the only alternative is no cryptography.  When feasible, sending
      and receiving agents should inform senders and recipients the
      relative cryptographic strength of messages.

   Extracted from S/MIME Version 3.1 Certificate Handling [11]:

      When processing certificates, there are many situations where the
      processing might fail.  Because the processing may be done by a
      user agent, a security gateway, or other program, there is no
      single way to handle such failures.  Just because the methods to
      handle the failures has not been listed, however, the reader
      should not assume that they are not important.  The opposite is
      true: if a certificate is not provably valid and associated with
      the message, the processing software should take immediate and
      noticeable steps to inform the end user about it.

      Some of the many places where signature and certificate checking
      might fail include:

      -  no Internet mail addresses in a certificate matches the sender
         of a message, if the certificate contains at least one mail
         address
      -  no certificate chain leads to a trusted CA
      -  no ability to check the Certificate Revocation List (CRL) for a
         certificate
      -  an invalid CRL was received
      -  the CRL being checked is expired
      -  the certificate is expired
      -  the certificate has been revoked

      There are certainly other instances where a certificate may be
      invalid, and it is the responsibility of the processing software
      to check them all thoroughly, and to decide what to do if the
      check fails.

   The following certificate types MUST be supported.
          With URL
          Without URL
          Self Certified
          Certification Authority Certified

   The complete certification chain MUST be included in all
   certificates.  All certificate verifications MUST "chain to root".
   Additionally, the certificate hash should match the hash recomputed
   by the receiver.

10.  References

10.1. Normative References

   [1]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message Bodies",
         RFC 2045, November 1996.

         Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part Two: Media Types", RFC 2046, November
         1996.

         Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part Five: Conformance Criteria and
         Examples", RFC 2049, November 1996.

   [2]   Crocker, D., "MIME Encapsulation of EDI Objects", RFC 1767,
         March 1995.

   [3]   Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
         RFC 959, October 1985.

   [4]   Horowitz, M. and S. Lunt, "FTP Security Extensions", RFC 2228,
         October 1997.

   [5]   Harding, T., Drummond, R., and C. Shih, "MIME-based Secure
         Peer-to-Peer Business Data Interchange over the Internet", RFC
         3335, September 2002.

   [6]   Hansen, T. and G. Vaudreuil, "Message Disposition
         Notification", RFC 3798, May 2004.

   [7]   Galvin, J., Murphy, S., Crocker, S., and N. Freed, "Security
         Multiparts for MIME: Multipart/Signed and Multipart/Encrypted",
         RFC 1847, October 1995.

   [8]   Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
         2001.

   [9]   Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852,
         July 2004.

   [10]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
         (S/MIME) Version 3.1 Message Specification", RFC 3851, July
         2004.

   [11]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
         (S/MIME) Version 3.1 Certificate Handling", RFC 3850, July
         2004.

   [12]  Vaudreuil, G., "The Multipart/Report Content Type for the
         Reporting of Mail System Administrative Messages", RFC 3462,
         January 2003.

   [13]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
         2246, January 1999.

   [14]  Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
         MESSAGES", STD 11, RFC 822, August 1982.

   [15]  Resnick, P., "Internet Message Format", RFC 2822, April 2001.

   [16]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
         RFC 3023, January 2001.

   [17]  Gutmann, P., "Compressed Data Content Type for Cryptographic
         Message Syntax (CMS)", RFC 3274, June 2002.

   [18]  Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217, October
         2005.

   [19]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

10.2. Informative References

   [20]  Harding, T., "Compressed Data for EDIINT", Work in Progress,
         January 2007.

   [21]  Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L., and L.
         Repka, "S/MIME Version 2 Message Specification", RFC 2311,
         March 1998.

   [22]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", RFC 4234, October 2005.

   [23]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.1", RFC 4346, April 2006.

Appendix A. Message Examples

   NOTE: All examples are provided as an illustration only, and are not
         considered part of the protocol specification.  If an example
         conflicts with the protocol definitions specified above or with
         that of a referenced RFC, the example is wrong.

A.1. Signed Message Requesting a Signed Receipt

   Date: Wed, 31 Jul 2002 13:34:50 GMT
   AS3-Version: 1.0
   AS3-From:  cyclone
   AS3-To: "trading partner"
   Message-Id: <200207310834482A70BF63@host.com>
   Disposition-Notification-To: ftp://host:port/mdnbox
   Disposition-Notification-Options: signed-receipt-
     protocol=optional,pkcs7-signature;
     signed-receipt-micalg=optional,sha1
   Content-Type: multipart/signed; boundary="as3BouNdary1as3";
      protocol="application/pkcs7-signature"; micalg=sha1
   Content-Length: 3075

   --as3BouNdary1as3
   Content-Type: application/edi-x12
   Content-Disposition: Attachment; filename=rfc1767.dat

   [ISA ...EDI transaction data...IEA...]

   --as3BouNdary1as3
   Content-Type: application/pkcs7-signature

     [omitted binary pkcs7 signature data]
   --as3BouNdary1as3--

A.2. MDN for Message A.1 Above

   Date: Wed, 31 Jul 2002 13:34:50 GMT
   AS3-From: "trading partner"
   AS3-To: cyclone
   AS3-Version: 1.0
   Message-ID: <709700825.1028122454671.JavaMail@ediXchange>
   Content-Type: multipart/signed; micalg=sha1;
     protocol="application/pkcs7-signature";
     boundary="----=_Part_57_648441049.1028122454671"
   Content-Length: 1024

   ------=_Part_57_648441049.1028122454671

   & Content-Type: multipart/report;
   &   Report-Type=disposition-notification;
   &   boundary="----=_Part_56_1672293592.1028122454656"
   &
   &------=_Part_56_1672293592.1028122454656
   &Content-Type: text/plain
   &Content-Transfer-Encoding: 7bit
   &
   &MDN for -
   & Message ID: <200207310834482A70BF63@host.com>
   &  From: cyclone
   &  To: "trading partner"
   &  Received on: 2002-07-31 at 09:34:14 (EDT)
   &  Status: processed
   &  Comment: This is not a guarantee that the message has been
   &  completely processed or understood by the receiving translator
   &
   &------=_Part_56_1672293592.1028122454656
   &   Content-Type: message/disposition-notification
   &   Content-Transfer-Encoding: 7bit
   &
   &   Reporting-UA: AS3 Server
   &   Original-Recipient: rfc822; "trading partner"
   &   Final-Recipient: rfc822; "trading partner"
   &   Original-Message-ID: <200207310834482A70BF63@host.com>
   &   Received-content-MIC: 7v7F++fQaNB1sVLFtMRp+dF+eG4=, sha1
   &   Disposition: automatic-action/MDN-sent-automatically; processed
   &
   &------=_Part_56_1672293592.1028122454656--

    ------=_Part_57_648441049.1028122454671
   Content-Type: application/pkcs7-signature; name=smime.p7s
   Content-Transfer-Encoding: base64
   Content-Disposition: attachment; filename=smime.p7s

   MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQ
   cp24hMJNbxDKHnlB9jTiQzLwSwo+/90Pc87x+Sc6EpFSUYWGAAAAAAAA
   ------=_Part_57_648441049.1028122454671--

   Notes:

      1. The lines proceeded with "&" are what the signature is
         calculated over.

      2. For details on how to prepare the multipart/signed with
         protocol="application/pkcs7-signature", see RFC 3851 [10],
         "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version
         3.1 Message Specification".

      3. Note that the textual first body part of the multipart/report
         can be used to include a more detailed explanation of the error
         conditions reported by the disposition headers.  The first body
         part of the multipart/report, when used in this way, allows a
         person to better diagnose a problem in detail.

      4. As specified by RFC 3462 [12], returning the original or
         portions of the original message in the third body part of the
         multipart/report is not required.  This is an optional body
         part.  However, it is RECOMMENDED that this body part be
         omitted or left blank.

Authors' Addresses

   Terry Harding
   Axway
   8388 E. Hartford Drive, Suite 100
   Scottsdale, AZ  85255 USA

   EMail: tharding@us.axway.com

   Richard Scott
   Axway
   8388 E. Hartford Drive, Suite 100
   Scottsdale, AZ  85255 USA

   EMail: rscott@us.axway.com

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