Introducing Digital Forensics
Peter Sommer
London School of Economics, UK
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
Digital Forensics
aka
• Computer Forensics
• Forensic Computing
• Digital Evidence
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
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
Digital Forensics
We are going to look at these issues mostly
via a case study
• Demonstrates most types of computerderived evidence
• Shows how a good complex case is put
together
• Illustrates various legal needs
• Shows how, after all this, a case may fail
Digital Forensics
But first, we need to introduce some
legal terminology, give a bit of
background ….
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)
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
Attributes of Good Evidence
• authentic
• accurate
• complete
Attributes of Good Evidence
• chain of custody / continuity of
evidence
• transparent forensic procedures
• accuracy of process
• accuracy of content
• explanations
The Case Study
Rome Labs
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
GAO Report
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
• 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
R v Richard Pryce
USAF Workstation
IBM Compatible
Modem
Lockheed WS
NASA WS
Datastream
Cowboy
USAF Workstation
IBM Compatible
Modem
Richard
Pryce
Lockheed WS
NASA WS
Datastream
Cowboy
USAF Workstation
IBM Compatible
Modem
Richard
Pryce
The Legal Problem:
How do you prove
the link?
Lockheed WS
NASA WS
USAF Workstation
IBM Compatible
Modem
How the hack
happened
Lockheed WS
NASA WS
London
USAF Workstation
IBM Compatible
Seattle
Modem
Internet
ptsn
Lockheed WS
NASA WS
Minicomputer
USAF Workstation
ptsn
USAF Workstation
Public switch
Bogota
USAF Workstation
How the hack
was monitored
USAF Monitor
USAF Workstation
IBM Compatible
Modem
BT Monitor
Shell
A/C
Lockheed WS
Phone
calls, time
duration
NASA WS
Minicomputer
USAF Workstation
USAF Workstation
Ethernet card
USAF Monitor
Public switch
IP
Monitor
USAF Workstation
How the hack
was monitored:
the evidence
Pryce’s
HDD
Target
logs,files
USAF Monitor
ISP
Info, logs
Unix logs,
Monitoring
progs
Phone
Logs
IBM Compatible
Modem
USAF Workstation
Target
logs,files
Lockheed WS
BT Monitor
NASA WS
Minicomputer
USAF Workstation
USAF Workstation
Ethernet card
USAF Monitor
Public switch
Network
Monitor Logs
USAF Workstation
Target
logs,files
Pryce’s
HDD
Target
logs,files
USAF Monitor
ISP
Info, logs
Unix logs,
Monitoring
progs
Phone
Logs
IBM Compatible
Modem
USAF Workstation
Target
logs,files
Lockheed WS
BT Monitor
NASA WS
Minicomputer
USAF Workstation
USAF Workstation
Target
logs,files
Ethernet card
USAF Monitor
Public switch
Network
Monitor Logs
Most of these have date/time stamps ...
USAF Workstation
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

Role of Defence Expert
• Acts under instruction - specific
instruction:
“Discard any admissions in interview;
show us the weaknesses in the
digital evidence …”
Pryce’s
HDD
Target
logs,files
USAF Monitor
ISP
Info, logs
Unix logs,
Monitoring
progs
Phone
Logs
IBM Compatible
Modem
USAF Workstation
Target
logs,files
Lockheed WS
BT Monitor
NASA WS
Minicomputer
USAF Workstation
USAF Workstation
Ethernet card
USAF Monitor
Public switch
No Records !
Network
Monitor Logs
USAF Workstation
Target
logs,files
Breaking the Digital Evidence
•
•
•
•
•
•
Pryce’s HDD
BT Call Monitor
ISP Monitored Shell A/c
ISP Own Statements
USAF Network Monitors
Target Records
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
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?
Breaking the Digital Evidence
BT Call Monitor
• records numbers dialled, time,
duration, not content
• inconsistent print-out
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?
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 !!

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
Breaking the Digital Evidence
Target Records
• freezing of scene
• continuity of evidence
• “I recognise ….”
• honey traps
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

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!
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
Introducing Digital Forensics
Peter Sommer
London School of Economics, UK