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Introduction to Digital Forensics: Investigating Computer Incidents for Legal Purposes

Discover the world of digital forensics and learn how to collect and analyze digital evidence that can be used in court. Explore real case studies and understand the legal aspects of digital investigations.

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Introduction to Digital Forensics: Investigating Computer Incidents for Legal Purposes

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  1. Introducing Digital Forensics Peter Sommer London School of Economics, UK

  2. Peter Sommer • academic at London School of Economics – Information Systems as opposed to “Computer Science” • 1st degree: Oxford Law • first forensic investigation – 1985 • since then: Rome Labs, Cathedral / Cheshire Cat, Buccaneer, murder, fraud, immigration, software and currency counterfeiting, warez, harassment, paedophilia, hacking, infotheft etc • Shrivenham MSc , Centrex LE training • UK experts have primary duty to the courts

  3. Digital Forensics aka • Computer Forensics • Forensic Computing • Digital Evidence

  4. Digital Forensics More than: • Investigating computer-related incidents • Incident Response But: • Collecting evidence and building a story that can be used in court – and if necessary lead to a conviction

  5. Digital Forensics Thus: • Everything you would need to do while investigating a computer incident • Making sure that some-one can test and verify everything you claim • Complying with the needs and peculiarities of the law

  6. Digital Forensics We are going to look at these issues mostly via a case study • Demonstrates most types of computer-derived evidence • Shows how a good complex case is put together • Illustrates various legal needs • Shows how, after all this, a case may fail

  7. Digital Forensics But first, we need to introduce some legal terminology, give a bit of background ….

  8. Evidence in Court Adversarial Criminal Procedure: As used in US, UK and former UK colonies • police investigate; prosecuting authority / DA prosecutes; judge is chairman / enunciator of law; jury decides issues of fact; prosecution and defence arguments presented by lawyers: • proof is what is demonstrated before the court (not what “scientists” or “experts” say they believe)

  9. Evidence in Court • Admissibility (legal rules decided by judge) • hearsay, documents, unfairness in acquisition • Fed. Rules, 4th Amendment; CALEA, PACE, 1984; CJA, 1988; RIPA, 2000; • Weight (issues of fact) • what persuades a court is not the same as scientific “proof” - Frye, Daubert, Kuomo Tire

  10. Attributes of Good Evidence • authentic • accurate • complete

  11. Attributes of Good Evidence • chain of custody / continuity of evidence • transparent forensic procedures • accuracy of process • accuracy of content • explanations

  12. The Case Study Rome Labs

  13. Rome Labs • March-April 1994 - classic teenage hack of USAF, NASA, Lockheed etc sites • Rome Labs, New York, paralysed for nearly 3 weeks • “The most serious attack on the US military without the declaration of hostilities” • … used in 1996 GAO Report, Congressional “Security in Cyberspace” hearings, etc as an examplar of Information Warfare

  14. GAO Report

  15. Rome Labs Sources: • I was hired by UK defense lawyers (in the English legal system) • The evidence before the UK courts • USAF investigators • Scotland Yard investigators • The perpetrators

  16. Important perpetrator: “Datastream Cowboy” • USAF investigator recalls IRC session with a “Datastream Cowboy” several months earlier - had provided London, UK, phone number • Via Scotland Yard Computer Crime Unit: phone number linked to Richard Pryce, 16 yrs old

  17. R v Richard Pryce

  18. Datastream Cowboy Richard Pryce

  19. Datastream Cowboy The Legal Problem: How do you prove the link? Richard Pryce

  20. How the hack happened

  21. London Seattle Internet ptsn ptsn Bogota

  22. How the hack was monitored

  23. Shell A/C Phone calls, time duration IP Monitor

  24. How the hack was monitored: the evidence

  25. Target logs,files Pryce’s HDD ISP Info, logs Unix logs, Monitoring progs Target logs,files Phone Logs Target logs,files Network Monitor Logs

  26. Target logs,files Pryce’s HDD ISP Info, logs Unix logs, Monitoring progs Target logs,files Phone Logs Target logs,files Network Monitor Logs Most of these have date/time stamps ...

  27. Role of Defence Expert Prior to trial - • explain evidence to lawyers • look for weaknesses At trial - • assist lawyers • (perhaps) give evidence • fact & opinion • answers must be complete

  28. Role of Defence Expert • Acts under instruction - specific instruction: “Discard any admissions in interview; show us the weaknesses in the digital evidence …”

  29. Target logs,files Pryce’s HDD ISP Info, logs Unix logs, Monitoring progs Target logs,files Phone Logs Target logs,files Network Monitor Logs No Records !

  30. Breaking the Digital Evidence • Pryce’s HDD • BT Call Monitor • ISP Monitored Shell A/c • ISP Own Statements • USAF Network Monitors • Target Records

  31. Breaking the Digital Evidence Pryce’s HDD • 170 MB ! • lots of hacking tools • partial logs of IRC sessions • password and IP address files • files apparently from some target computers • music-related files

  32. Breaking the Digital Evidence Pryce’s HDD • disk imaging - evidence preservation • print-outs • PII certificate - sensitive files • recovered data • corrupted files • was there more than one source for target password files?

  33. Breaking the Digital Evidence BT Call Monitor • records numbers dialled, time, duration, not content • inconsistent print-out

  34. Breaking the Digital Evidence ISP Monitored Shell A/c • ps, w, automated, semi-automated, manual • how were evidential print-outs controlled and preserved? • team effort - who reports?

  35. Breaking the Digital Evidence ISP Monitored Shell A/c • print-out depends on accuracy of: • ISP CyberSpace machine • computers hosting monitoring facilities • monitoring programs - disclosure • human operators • continuity of evidence • clock timings !!

  36. Breaking the Digital Evidence USAF Network Monitor • monitors IP traffic on sub-net • principle is OK, but how achieved? • monitoring point(s) • quality of program - disclosure • continuity of evidence • team work

  37. Breaking the Digital Evidence Target Records • freezing of scene • continuity of evidence • “I recognise ….” • honey traps

  38. Lessons from Rome Labs • Hackers invented no new techniques but used existing ones well with great determination and stamina • USAF computers • poorly secured • fixed IP addresses, default passwords • little use of CERT etc advisories

  39. Lessons from Rome Labs • Hackers were often rejected; would have had many more failures with better elementary security • US investigators hampered by internal jurisdictional boundaries • US investigators had very little training in evidence collection • US/UK collaboration was quite good!

  40. Conclusions • Digital Evidence alone would have been insufficient • Good technical methods alone would not have worked • Effects of team efforts • Poor evidence continuity • Disclosure of methods issues

  41. Introducing Digital Forensics Peter Sommer London School of Economics, UK

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