Digital Forensics

1
Digital Forensics

• Dr. Bhavani Thuraisingham
• The University of Texas at Dallas
• Lecture 3
• Computer Forensics Data Recovery and Evidence
  Collection and Preservation
• September 3, 2008

2
Data Recovery

• What is Data Recovery?
• Role of Backup in Data Recovery
• Data Recovery Solution
• Hiding and Recovering Hidden Data

3
What is Data Recovery

• Usually data recovery means that data that is
  lost is recovered e.g., when a system crashes
  some data may be lost, with appropriate recovery
  procedures the data is recovered
• In digital forensics, data recovery is about
  extracting the data from seized computers (hard
  drives, disks etc.) for analysis

4
Role of Backup in Data Recovery

• Databases/files are backed up periodically
  (daily, weekly, hourly etc.) so that if system
  crashes the databases/files can be recovered to
  the previous consistent state
• Challenge to backup petabyte sized
  databases/files
• Obstacles for backing up
• Backup window, network bandwidth, system
  throughout
• Current trends
• Storage cost decreasing, systems have to be
  online 24x7
• Next generation solutions
• Multiple backup servers, optimizing storage space

5
Data Recovery/Backup Solution

• Develop a plan/policy for backup and recovery
• Develop/Hire/Outsource the appropriate expertise
• Develop a system design for backup/recovery
• Three tier architectures, caches, backup servers
• Examine state of the art backup/recovery products
  and tools
• Implement the backup plan according to the policy
  and design

6
Recover Hidden Data

• Hidden data
• Files may be deleted, but until they are
  overwritten, the data may remain
• Data stored in diskettes and stored insider
  another disk
• Need to get all the pieces and complete the
  puzzle
• Analysis techniques (including statistical
  reasoning) techniques are being used to recover
  hidden data and complete the puzzle
• Reference
• http//www.forensicfocus.com/hidden-data-analysis-
  ntfs

7
Evidence Collection and Data Seizure

• What is Evidence Collection
• Types of Evidence
• Rules of Evidence
• Volatile Evidence
• Methods of Collection
• Steps to Collection
• Controlling Contamination

8
What is Evidence Collection

• Collecting information from the data recovered
  for further analysis
• Need to collect evidence so that the attacker can
  be found and future attacks can be prevented
  and/or limited
• Collect evidence for analysis or monitor the
  intruder
• Obstacles
• Difficult to extract patterns or useful
  information from the recovered data
• Difficult to tie the extracted information to a
  person

9
Types of Evidence

• Testimonial Evidence
• Evidence supplied by a witness subject to the
  perceived reliability of the witness
• Word processor documents written by a witness as
  long as the author states that he wrote it
• Hearsay
• Evidence presented by a person who is not a
  direct witness
• Word processor documents written by someone
  without direct knowledge of the incident

10
Rules of Evidence

• Admissible
• Evidence must be able to be used in court
• Authentic
• Tie the evidence positively to an incident
• Complete
• Evidence that can cover all perspectives
• Reliable
• There should be no doubt that proper procedures
  were used
• Believable
• Understandable and believable to a jury

11
Additional considerations

• Minimize handling and corruption of original data
• Account for any changes and keep detailed logs
• Comply with the 5 basic rules
• Do not exceed your knowledge need to understand
  what you are doing
• Follow the security policy established
• Work fast / however need to be accurate
• Proceed from volatile to persistent evidence
• Do not shut down the machine before collecting
  evidence
• Do not run programs on the affected machine

12
Volatile Evidence

• Types
• Cached data
• Routing tables
• Process table
• Kernel statistics
• Main memory
• What to do next
• Collect the volatile data and store in a
  permanent storage device

13
Methods of Collection

• Freezing the scene
• Taking a snapshot of the system and its
  compromised state
• Recover data, extract information, analyze
• Honeypotting
• Create a replica system and attract the attacker
  for further monitoring

14
Steps to Collection

• Find the evidence where is it stored
• Find relevant data - recovery
• Create order of volatility
• Remove external avenues of change no tampering
• Collect evidence use tools
• Good documentation of all the actions

15
Controlling Contamination

• Once the data is collected it should not be
  contaminated, must be stored in a secure place,
  encryption techniques
• Maintain a chain of custody, who owns the data,
  data provenance techniques
• Analyze the evidence
• Use analysis tools to determine what happened
• Analyze the log files and determine the timeline
• Analyze backups using a dedicated host
• Reconstruct the attack from all the information
  collected

16
Duplication and Preservation of Evidence

• Preserving the Digital Crime Scene
• First task is to make a compete bit stream backup
  of all computer data before review or process
• Bit stream backups (also referred to as mirror
  image backups) involve the backup of all areas of
  a computer hard disk drive or another type of
  storage media, e.g., Zip disks, floppy disks,
  Jazz disks, etc. Such backups exactly replicate
  all sectors on a given storage device. Thus, all
  files and ambient data storage areas are copied.
  Bit stream backups are sometimes also referred to
  as 'evidence grade' backups and they differ
  substantially from traditional computer file
  backups and network server backups.
• http//www.forensics-intl.com/def2.html
• Make sure that the legal requirements are met and
  proper procedures are followed

17
Digital Evidence Process Model

• The U.S. Department of Justice published a
  process model in the Electronic Crime Scene
  Investigation A guide to first responders that
  consists of four phases -
• 1. Collection which involves the evidence
  search, evidence recognition, evidence collection
  and documentation.
• 2. Examination this is designed to facilitate
  the visibility of evidence, while explaining its
  origin and significance. It involves revealing
  hidden and obscured information and the relevant
  documentation.
• 3. Analysis this looks at the product of the
  examination for its significance and probative
  value to the case.
• 4. Reporting this entails writing a report
  outlining the examination process and pertinent
  data recovered from the overall investigation.
• https//www.dfrws.org/2004/day1/Tushabe_EIDIP.pdf

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Standards for Digital Evidence

• The Scientific Working Group on Digital Evidence
  (SWGDE) was established in February 1998 through
  a collaborative effort of the Federal Crime
  Laboratory Directors. SWGDE, as the U.S.-based
  component of standardization efforts conducted by
  the International Organization on Computer
  Evidence (IOCE), was charged with the development
  of cross-disciplinary guidelines and standards
  for the recovery, preservation, and examination
  of digital evidence, including audio, imaging,
  and electronic devices.
• The following document was drafted by SWGDE and
  presented at the International Hi-Tech Crime and
  Forensics Conference (IHCFC) held in London,
  United Kingdom, October 4-7, 1999. It proposes
  the establishment of standards for the exchange
  of digital evidence between sovereign nations and
  is intended to elicit constructive discussion
  regarding digital evidence. This document has
  been adopted as the draft standard for U.S. law
  enforcement agencies.
• http//www.fbi.gov/hq/lab/fsc/backissu/april2000/s
  wgde.htm

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Verifying Digital Evidence

• Encryption techniques
• Public/Private key encryption
• Certification Authorities
• Digital ID/Credentials
• Owner signs document with his private key, the
  Receiver decrypts the document with the owners
  public key
• Owner signs document with the receivers public
  key, Receiver decrypts the document with his
  private key
• Standards for Encryption
• Export/Import laws
• http//esm.cis.unisa.edu.au/new_esml/resources/pub
  lications/digital20forensics20-20exploring20va
  lidation,20verification20and20certification.pdf
  

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Conclusion - I

• Data must be backed up using appropriate
  policies, procedures and technologies
• Once a crime ahs occurred data ahs to be
  recovered from the various disks and commuters
• Data that is recovered has to be analyzed to
  extract evidence
• Evidence has to analyzed to determine what
  happened
• Use log files and documentations to establish the
  timeline
• Reconstruct the attack

21
Conclusion - II

• Standards and processes have to be set in place
  for representing, preserving, duplicating,
  verifying, validating certifying and accrediting
  digital evidence
• Numerous techniques are out there need to
  determine which ones are useful for the
  particular evidence at hand
• Need to make it a scientific discipline

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Links

• Data Recovery
• http//www.datatexcorp.com/
• http//www.forensicfocus.com/hidden-data-analysis-
  ntfs
• Digital Evidence
• http//faculty.ncwc.edu/toconnor/426/426lect06.htm
  
• http//www.itoc.usma.edu/Workshop/2006/Program/Pre
  sentations/IAW2006-07-1.pdf
• http//www.e-evidence.info/index.html
• http//www.digital-evidence.org/
• http//findarticles.com/p/articles/mi_m2194/is_3_7
  3/ai_n6006624/pg_1
• http//infohost.nmt.edu/sfs/Students/HarleyKozush
  ko/Presentations/DigitalEvidence.pdf

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Links Preserving Digital Evidence

• Preserving Digital Evidence
• http//www.fbi.gov/hq/lab/fsc/backissu/april2000/s
  wgde.htm (standards)
• https//www.dfrws.org/2004/day1/Tushabe_EIDIP.pdf
  (process)
• http//www.logicube.com/logicube/articles/cybersle
  uth_collecting_digital_evidence.asp (hard drive
  duplication)
• http//www.crime-scene-investigator.net/admissibil
  ityofdigital.html (digital photographs)
• http//faculty.ncwc.edu/toconnor/426/426lect06.htm
  
• http//www.freepatentsonline.com/7181560.html (US
  Patent)
• http//www.mediasec.com/downloads/veroeffentlichun
  gen/thorwirth2004.pdf (survey)
• http//www.forensics-intl.com/def2.html (bit
  stream backup)

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Links Verifying Digital Evidence

• Verifying Digital Evidence
• http//esm.cis.unisa.edu.au/new_esml/resources/pub
  lications/digital20forensics20-20exploring20va
  lidation,20verification20and20certification.pdf
  (verification and validation)
• http//www.forensicmag.com/articles.asp?pid21
• http//www.forensicmag.com/articles.asp?pid28
  (accreditation, parts 1 and 2)