1. Dr. Bhavani Thuraisingham The University of Texas at Dallas
Digital Forensics
Dr. Bhavani Thuraisingham
The University of Texas at Dallas
Lecture #3
Computer Forensics Data Recovery and Evidence Collection and Preservation
August 31, 2009

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:
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.
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.

18. 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, 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.

19. 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 owner’s public key
Owner signs document with the receiver’s public key, Receiver decrypts the document with his private key
Standards for Encryption
Export/Import laws
%20exploring%20validation,%20verification%20and%20certification.pdf

20. 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

22. Links Data Recovery http://www.datatexcorp.com/
Digital Evidence
entations/IAW pdf
/pg_1
Presentations/DigitalEvidence.pdf

23. Links: Preserving Digital Evidence
(standards)
(process)
ing_digital_evidence.asp (hard drive duplication)
investigator.net/admissibilityofdigital.html (digital photographs)
(US Patent)
rwirth2004.pdf (survey)
(bit stream backup)

24. Links: Verifying Digital Evidence
tions/digital%20forensics%20- %20exploring%20validation,%20verification%20and%20 certification.pdf (verification and validation)
(accreditation, parts 1 and 2)