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