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Digital Forensics

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Digital Forensics

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  1. Digital Forensics Dr. Bhavani Thuraisingham The University of Texas at Dallas Computer Forensics Data Recovery and Evidence Collection and Preservation September 7, 2011

  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: •

  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, 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. •

  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,%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 • • • Digital Evidence • • • • • •

  23. Links: Preserving Digital Evidence • Preserving Digital Evidence • (standards) • (process) • (hard drive duplication) • (digital photographs) • • (US Patent) • (survey) • (bit stream backup)

  24. Links: Verifying Digital Evidence • Verifying Digital Evidence •,%20verification%20and%20certification.pdf (verification and validation) • • (accreditation, parts 1 and 2)