2013-10-18 Computer Forensics and Hash Values
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A presentation delivered to the New Hampshire Association of Criminal Defense Lawyers on October 18, 2013.
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2013-10-18 Computer Forensics and Hash Values
- 1. Computer Forensics: Images and Integrity Frederick S. Lane NHACDL Fall 2013 CLE Concord, NH 18 October 2013 www.FrederickLane.com www.ComputerForensicsDigest.com
- 2. Background and Expertise • Attorney and Author of 7 Books • Computer Forensics Expert -- 15 years • Over 100 criminal cases • Lecturer on ComputerRelated Topics – 20+ years • Computer user (midframes, desktops, laptops) – 35+ years
- 3. Lecture Overview • Not Your Mother’s Hash • The Role of Hash Values in Computer Forensics • The Growing Use of Hash Flags • P2P Investigations Using Hash Values
- 4. Not Your Mother’s Hash • Cryptograhic Hash Values • Relatively Easy to Generate • Extremely Difficult to Determine Original Data from Hash Value • Extremely Difficult to Change Data without Changing Hash • Extremely Unlikely that Different Data Will Produce the Same Hash Value
- 5. Types of Hash Alogirithms • Secure Hash Algorithm • Developed by NIST in 1995 • 40 characters long • Message Digest • Developed by Prof. Rivest in 1990 • 32 characters long • Photo DNA • Developed by Microsoft • Hash value based on histograms of multiple section of image
- 6. Complex Explanation • The word DOG can be represented in different ways: • Binary: 010001000110111101100111 • Hexadecimal: 646f67 • A hash algorithm converts the hexadecimal value to a fixed-length hexadecimal string. • SHA-1: e49512524f47b4138d850c9d9d85972927281 da0 • MD5: 06d80eb0c50b49a509b49f2424e8c805
- 7. Complex Explanation • Changing a single letter changes each value. • For instance, the word COG produces the following values: • Binary: 010000110110111101100111 • Hexadecimal: 436f67 • SHA-1: d3da816674b638d05caa672f60f381ff504e578c • MD5: 01e33197684afd628ccf82a5ae4fd6ad
- 9. Evidence Integrity • Acquisition Hashes • Creation of Mirror Images • Verification of Accuracy of Mirror Images • Use of “Known File Filter” • Hashkeeper • National Software Reference Library • NCMEC CVIP Database
- 10. Growing Use of Hash Flags • Child Protection and Sexual Predator Act of 1998 • 2008: ISPs Agree to Block Access to Known Sources of CP and to Scan for NCMEC Hash Values • SAFE Act: Requires ISPs and OSPs to Turn Over Subscriber Info If Known CP Is Identified
- 11. P2P Hash Values • Basic Operation of Peer-toPeer Networks • • • • Decentralized Distribution Gnutella and eDonkey Client Software Hash Values Associated with Each File
- 12. Automated P2P Searches • Peer Spectre or Nordic Mule Scans for IP Addresses of Devices Offering to Share Known CP Files • IP Addresses Are Stored by TLO in Child Protection System • Officers Conduct “Undercover” Investigations by Reviewing Spreadsheets of Hits in CPS
- 13. Growing Defense Concerns • No Independent Examination of Proprietary Software • Very Little Information Regarding TLO or CPS • Peer Spectre May Generate False Hits Due to Normal Operation of P2P Clients • Search Warrant Affidavits Fail to Mention Role of TLO or CPS
- 14. Computer Forensics: Images and Integrity Frederick S. Lane NHACDL Fall 2013 CLE Concord, NH 18 October 2013 www.FrederickLane.com www.ComputerForensicsDigest.com