Network Working Group                                       D. Brezinski
Request for Comments: 3227                                      In-Q-Tel
BCP: 55                                                      T. Killalea
Category: Best Current Practice                                neart.org
                                                           February 2002

Guidelines for Evidence Collection and Archiving

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

Abstract

   A "security incident" as defined in the "Internet Security Glossary",
   RFC 2828, is a security-relevant system event in which the system's
   security policy is disobeyed or otherwise breached.  The purpose of
   this document is to provide System Administrators with guidelines on
   the collection and archiving of evidence relevant to such a security
   incident.

   If evidence collection is done correctly, it is much more useful in
   apprehending the attacker, and stands a much greater chance of being
   admissible in the event of a prosecution.

   1 Introduction.................................................... 2
     1.1 Conventions Used in this Document........................... 2
   2 Guiding Principles during Evidence Collection................... 3
     2.1 Order of Volatility......................................... 4
     2.2 Things to avoid............................................. 4
     2.3 Privacy Considerations...................................... 5
     2.4 Legal Considerations........................................ 5
   3 The Collection Procedure........................................ 6
     3.1 Transparency................................................ 6
     3.2 Collection Steps............................................ 6
   4 The Archiving Procedure......................................... 7
     4.1 Chain of Custody............................................ 7
     4.2 The Archive................................................. 7
   5 Tools you'll need............................................... 7

   6 References...................................................... 8
   7 Acknowledgements................................................ 8
   8 Security Considerations......................................... 8
   9 Authors' Addresses.............................................. 9
   10 Full Copyright Statement.......................................10

1 Introduction

   A "security incident" as defined in [RFC2828] is a security-relevant
   system event in which the system's security policy is disobeyed or
   otherwise breached.  The purpose of this document is to provide
   System Administrators with guidelines on the collection and archiving
   of evidence relevant to such a security incident.  It's not our
   intention to insist that all System Administrators rigidly follow
   these guidelines every time they have a security incident.  Rather,
   we want to provide guidance on what they should do if they elect to
   collect and protect information relating to an intrusion.

   Such collection represents a considerable effort on the part of the
   System Administrator.  Great progress has been made in recent years
   to speed up the re-installation of the Operating System and to
   facilitate the reversion of a system to a 'known' state, thus making
   the 'easy option' even more attractive.  Meanwhile little has been
   done to provide easy ways of archiving evidence (the difficult
   option).  Further, increasing disk and memory capacities and the more
   widespread use of stealth and cover-your-tracks tactics by attackers
   have exacerbated the problem.

   If evidence collection is done correctly, it is much more useful in
   apprehending the attacker, and stands a much greater chance of being
   admissible in the event of a prosecution.

   You should use these guidelines as a basis for formulating your
   site's evidence collection procedures, and should incorporate your
   site's procedures into your Incident Handling documentation.  The
   guidelines in this document may not be appropriate under all
   jurisdictions.  Once you've formulated your site's evidence
   collection procedures, you should have law enforcement for your
   jurisdiction confirm that they're adequate.

1.1 Conventions Used in this Document

   The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
   and "MAY" in this document are to be interpreted as described in "Key
   words for use in RFCs to Indicate Requirement Levels" [RFC2119].

2 Guiding Principles during Evidence Collection

      -  Adhere to your site's Security Policy and engage the
         appropriate Incident Handling and Law Enforcement personnel.

      -  Capture as accurate a picture of the system as possible.

      -  Keep detailed notes.  These should include dates and times.  If
         possible generate an automatic transcript.  (e.g., On Unix
         systems the 'script' program can be used, however the output
         file it generates should not be to media that is part of the
         evidence).  Notes and print-outs should be signed and dated.

      -  Note the difference between the system clock and UTC.  For each
         timestamp provided, indicate whether UTC or local time is used.

      -  Be prepared to testify (perhaps years later) outlining all
         actions you took and at what times.  Detailed notes will be
         vital.

      -  Minimise changes to the data as you are collecting it.  This is
         not limited to content changes; you should avoid updating file
         or directory access times.

      -  Remove external avenues for change.

      -  When confronted with a choice between collection and analysis
         you should do collection first and analysis later.

      -  Though it hardly needs stating, your procedures should be
         implementable.  As with any aspect of an incident response
         policy, procedures should be tested to ensure feasibility,
         particularly in a crisis.  If possible procedures should be
         automated for reasons of speed and accuracy.  Be methodical.

      -  For each device, a methodical approach should be adopted which
         follows the guidelines laid down in your collection procedure.
         Speed will often be critical so where there are a number of
         devices requiring examination it may be appropriate to spread
         the work among your team to collect the evidence in parallel.
         However on a single given system collection should be done step
         by step.

      -  Proceed from the volatile to the less volatile (see the Order
         of Volatility below).

      -  You should make a bit-level copy of the system's media.  If you
         wish to do forensics analysis you should make a bit-level copy
         of your evidence copy for that purpose, as your analysis will
         almost certainly alter file access times.  Avoid doing
         forensics on the evidence copy.

2.1 Order of Volatility

   When collecting evidence you should proceed from the volatile to the
   less volatile.  Here is an example order of volatility for a typical
   system.

      -  registers, cache

      -  routing table, arp cache, process table, kernel statistics,
         memory

      -  temporary file systems

      -  disk

      -  remote logging and monitoring data that is relevant to the
         system in question

      -  physical configuration, network topology

      -  archival media

2.2 Things to avoid

   It's all too easy to destroy evidence, however inadvertently.

      -  Don't shutdown until you've completed evidence collection.
         Much evidence may be lost and the attacker may have altered the
         startup/shutdown scripts/services to destroy evidence.

      -  Don't trust the programs on the system.  Run your evidence
         gathering programs from appropriately protected media (see
         below).

      -  Don't run programs that modify the access time of all files on
         the system (e.g., 'tar' or 'xcopy').

      -  When removing external avenues for change note that simply
         disconnecting or filtering from the network may trigger
         "deadman switches" that detect when they're off the net and
         wipe evidence.

2.3 Privacy Considerations

      -  Respect the privacy rules and guidelines of your company and
         your legal jurisdiction.  In particular, make sure no
         information collected along with the evidence you are searching
         for is available to anyone who would not normally have access
         to this information.  This includes access to log files (which
         may reveal patterns of user behaviour) as well as personal data
         files.

      -  Do not intrude on people's privacy without strong
         justification.  In particular, do not collect information from
         areas you do not normally have reason to access (such as
         personal file stores) unless you have sufficient indication
         that there is a real incident.

      -  Make sure you have the backing of your company's established
         procedures in taking the steps you do to collect evidence of an
         incident.

2.4 Legal Considerations

   Computer evidence needs to be

      -  Admissible:  It must conform to certain legal rules before it
         can be put before a court.

      -  Authentic:  It must be possible to positively tie evidentiary
         material to the incident.

      -  Complete:  It must tell the whole story and not just a
         particular perspective.

      -  Reliable:  There must be nothing about how the evidence was
         collected and subsequently handled that casts doubt about its
         authenticity and veracity.

      -  Believable:  It must be readily believable and understandable
         by a court.

3 The Collection Procedure

   Your collection procedures should be as detailed as possible.  As is
   the case with your overall Incident Handling procedures, they should
   be unambiguous, and should minimise the amount of decision-making
   needed during the collection process.

3.1 Transparency

   The methods used to collect evidence should be transparent and
   reproducible.  You should be prepared to reproduce precisely the
   methods you used, and have those methods tested by independent
   experts.

3.2 Collection Steps

      -  Where is the evidence?  List what systems were involved in the
         incident and from which evidence will be collected.

      -  Establish what is likely to be relevant and admissible.  When
         in doubt err on the side of collecting too much rather than not
         enough.

      -  For each system, obtain the relevant order of volatility.

      -  Remove external avenues for change.

      -  Following the order of volatility, collect the evidence with
         tools as discussed in Section 5.

      -  Record the extent of the system's clock drift.

      -  Question what else may be evidence as you work through the
         collection steps.

      -  Document each step.

      -  Don't forget the people involved.  Make notes of who was there
         and what were they doing, what they observed and how they
         reacted.

   Where feasible you should consider generating checksums and
   cryptographically signing the collected evidence, as this may make it
   easier to preserve a strong chain of evidence.  In doing so you must
   not alter the evidence.

4 The Archiving Procedure

Evidence must be strictly secured. In addition, the Chain of Custody
needs to be clearly documented.

4.1 Chain of Custody

   You should be able to clearly describe how the evidence was found,
   how it was handled and everything that happened to it.

   The following need to be documented

      -  Where, when, and by whom was the evidence discovered and
         collected.

      -  Where, when and by whom was the evidence handled or examined.

      -  Who had custody of the evidence, during what period.  How was
         it stored.

      -  When the evidence changed custody, when and how did the
         transfer occur (include shipping numbers, etc.).

4.2 Where and how to Archive

   If possible commonly used media (rather than some obscure storage
   media) should be used for archiving.

   Access to evidence should be extremely restricted, and should be
   clearly documented.  It should be possible to detect unauthorised
   access.

5 Tools you'll need

   You should have the programs you need to do evidence collection and
   forensics on read-only media (e.g., a CD).  You should have prepared
   such a set of tools for each of the Operating Systems that you manage
   in advance of having to use it.

   Your set of tools should include the following:

      -  a program for examining processes (e.g., 'ps').

      -  programs for examining system state (e.g., 'showrev',
         'ifconfig', 'netstat', 'arp').

      -  a program for doing bit-to-bit copies (e.g., 'dd', 'SafeBack').

      -  programs for generating checksums and signatures (e.g.,
         'sha1sum', a checksum-enabled 'dd', 'SafeBack', 'pgp').

      -  programs for generating core images and for examining them
         (e.g., 'gcore', 'gdb').

      -  scripts to automate evidence collection (e.g., The Coroner's
         Toolkit [FAR1999]).

   The programs in your set of tools should be statically linked, and
   should not require the use of any libraries other than those on the
   read-only media.  Even then, since modern rootkits may be installed
   through loadable kernel modules, you should consider that your tools
   might not be giving you a full picture of the system.

   You should be prepared to testify to the authenticity and reliability
   of the tools that you use.

6 References

   [FAR1999]   Farmer, D., and W Venema, "Computer Forensics Analysis
               Class Handouts", http://www.fish.com/forensics/

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2196]   Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
               September 1997.

   [RFC2350]   Brownlee, N. and  E. Guttman, "Expectations for Computer
               Security Incident Response", FYI 8, RFC 2350, June 1998.

   [RFC2828]   Shirey, R., "Internet Security Glossary", FYI 36, RFC
               2828, May 2000.

7 Acknowledgements

   We gratefully acknowledge the constructive comments received from
   Harald Alvestrand, Byron Collie, Barbara Y. Fraser, Gordon Lennox,
   Andrew Rees, Steve Romig and Floyd Short.

8 Security Considerations

This entire document discuses security issues.

9 Authors' Addresses

   Dominique Brezinski
   In-Q-Tel
   1000 Wilson Blvd., Ste. 2900
   Arlington, VA 22209
   USA

   EMail: dbrezinski@In-Q-Tel.org

   Tom Killalea
   Lisi/n na Bro/n
   Be/al A/tha na Muice
   Co. Mhaigh Eo
   IRELAND

   Phone: +1 206 266-2196
   EMail: tomk@neart.org

10. Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.