Computer Forensics - Sonntag...evidence, but normally its just called “evidence”! Computer Forensics : Introduction 18 Types of evidence Who was it: Identifying information »

April 2015

Michael Sonntag

Computer Forensics An Introduction

What is "Computer Forensics"?

Computer Forensics (CF) is obtaining digital evidence › Analogue evidence is usually not considered here: Use "ordinary"

forensics to gather/evaluate

Analogue computers are almost non-existing today!

» This may come from running systems or parts of them › Hard disks, flash drives, PDAs, mobile phones, telephones, copiers, “pads”,

game devices, TVs etc.

» Can be evidence for computer crimes (computer fraud, hacking, …) or any other crime (documents with plans for x) or for various other uses

One indispensable issue is "data integrity"

Data is easily changeable: Evidence is then and only then usable in proceedings, if it is

ensured, that it has not been changed!

Computer Forensics : Introduction 2

What is "Computer Forensics"?

Other definitions:

» "Analytical techniques to identify, collect, preserve and examine evidence/information which is magnetically stored or encoded"

› Problem: "magnetically" Flash disks, running systems?

› Better: "in computerized systems and their parts"

» "We define computer forensics as the discipline that combines elements of law and computer science to collect and analyze data from computer systems, networks, wireless communi-cations, and storage devices in a way that is admissible as evidence in a court of law."

› Focus on legal proceedings; there are many other uses as well!

Note that this almost the "highest" form: If evidence is sufficient for criminal proceedings, it can be used for everything else as well!

» "A technological, systematic inspection of the computer system and its contents for evidence or supportive evidence of a crime or other computer use that is being inspected."


Important elements of a definition

Elements of computer forensics:

» “Digital data”: No analogue data, only data for/from automatic processing

» “History”: Only small parts ( further effects) affect the future › Most of it is “digital archaeology”!

» “Systematic”: We don’t collect something; we follow proce-dures to acquire and investigate that data, which we need later

» “Preserve”: Evidence might be needed later on › Someone else should be able to repeat it

› Might be needed as evidence in legal proceedings

» “Find”: Most elements of CF are not documented and must first be identified (e.g. what registry key will change when)

» “Evaluate”: Why did this change happen? › Finding some reason is simple, but have we identified all of them?

Timestamp is set on copying Was set File was copied! But what other actions exist that change timestamps identically?

Preserve first, find later!


Investigative aims: Technical

CF should answer some/all of these questions:

» Has something happened at all? › Random effect (e.g. memory error), bugs, …

» When did it happen? › How long had the attacker access to our files?

» What has happened and what are the effects? › What are the results from the intrusion?

» Who (=which computer system) was responsible for it? › Can we identify an IP address?

» How did he do it? › So we can block this in the future

» Why were we attacked? › Just “some computer” or deliberate attack; damage/gain; …

Uncovering what really occurred on a technical level


Investigative aims: Other

CF should answer some/all of these questions:

» What damage was caused? › Directly, cost of recovery, additional costs (loss of reputation, lost sales

etc.) – Not necessarily task of computer forensics expert!

» Who was responsible for it? › Moving from IP addresses, domain names etc. to names of human or legal

persons

» Providing evidence and a report for court proceedings › We don’t just need to know it, we must be able to prove it too!

Includes the method(s) of investigation, keeping evidence intact, …

› What are we unable to prove?

To minimize the impact on legal proceedings/avoid them

› How “good” is the evidence?

Commercial/legal aspects are also part of computer forensics!


Process of a forensic investigation

Presentation of results Presentation, report, expertise,

explanation in court, …

Investigation Desired analysis + estimate on correctness/probabilities

Validation: Unchanged? Intentionally manipulated?

Data acquisition „Chain of Custody“: Identity & Integrity

Documentation

Assignment What is to be investigated?

Location, content & time restrictions

Identification

Preservation

Collection


The basic principles of CF

No action to secure/collect evidence should affect its integrity

» It becomes much less worth/completely worthless!

Examiners should be trained

» Only investigate as far as your knowledge goes

All activities should be logged

» Seizure, examination, storage, and transfer › Complete chain of custody (including its security measures)

» Documented, preserved, and available for review › Proof for the chain of custody

Investigations must be accurate and impartial

» Computer forensic prosecutor/attorney/judge › Describe what was actually found

And what should have been found, but was missing!

› Describe how reliable these facts are

› Describe what conclusions can reasonably be drawn from it


The basic principles of CF

Similar (identical) principles, but seen from view of police » No action taken by law enforcement agencies or their agents should

change data held on a computer or storage media which may subsequently be relied upon in court.

» In circumstances where a person finds it necessary to access original data held on a computer or on storage media, that person must be competent to do so and be able to give evidence explaining the relevance and the implications of their actions.

» An audit trail or other record of all processes applied to computer-based electronic evidence should be created and preserved. An independent third party should be able to examine those processes and achieve the same result.

» The person in charge of the investigation (the case officer) has overall responsibility for ensuring that the law and these principles are adhered to.

Association of Chief Police Officers: Good Practice Guide for Computer-Based Electronic Evidence, http://www.7safe.com/electronic_evidence/ACPO_guidelines_computer_evidence.pdf


Requirements of for. procedures

How do we ensure these principles?

Follow standard/accepted procedures, which must fulfil:

» Acceptance: Method and procedure must be described in publications and be generally accepted

› New methods/procedures are possible, but may need proof of working and correctness

» Believability: Robustness and functionality of methods must have been proven

» Repeatability: If another persons does the same things to the same base material, the results must be identical

» Integrity: No undetected changes (side effects) may be introduced through investigation; integrity must be provable

» Reasons & consequences: Logical connections between events and traces in the evidence must be possible

» Documentation: Every step in the investigation must be adequately documented


When to use CF?

To provide digital evidence of specific activity

» In general, proving non-activity might also be the goal, but this is more difficult and only sometimes possible!

For legal proceedings

» Criminal cases: Child pornography, (computer) fraud, ...

» Civil cases: Hacking, information theft, industry espionage, …

Recovering data

» (Inadvertently) deleted information

Identifying weaknesses

» After a break in, identify the method employed to prevent it in the future

Identifying the attack/attacker

» Verify, whether an incident actually happened and who was responsible for it


Concrete examples

Misuse of ICT by employees

» Unauthorized disclosure of data

» Internet (WWW, E-Mail, …) abuse

» Deleted/damaged information

Exploiting ICT

» Industrial espionage

» Hacking of systems

» Infiltration (zombie, trojans, viruses, …)

Damaging ICT

» Web page defacements

» Denial of Service attacks

» Crashing computers


More (prosaic) examples

Any normal crime

» Plans on computer

» Tracing communication or money

Computer crimes

» Phishing, "money mules" etc.

Disputes between companies

» We did deliver the product

» The delivery was too late, defective, …

» Information theft, intentionality of trade mark misuse, …

Companies vs. consumers

» Details: See above!

» Addition: Often "computer company" vs. "laymen"


Problematic example

"Prove, that we did not receive this E-Mail"

Can we really do that?

» We can "easily" prove the receipt of the E-Mail, we just have to find it on the mail server (or traces of it)!

But proving the negative?

» If we don't find any trace on the mail server, this means › we did not search thoroughly enough,

› it was there, but later on accidentally deleted and overwritten,

› it was there and then intentionally and cleverly deleted, or

› it was never on the server at all (deleted in transit, …)!

» But there is normally no way to prove which of these options describe what actually occurred

Potential options: Third parties (logs, replies, …), traces of destroying evidence (no proof, but bad in court!)


When NOT to use CF!

Immediately acting when having any suspicion

» Plan first: Evidence is destroyed very easily!

» Locate an expert for doing this type of computer forensics

At the last minute: Do it as soon as possible

Because I’m interested: Girl-/Boyfriend, spouses etc.

» Pot. typical area for CF, but should not be used “lightly”!

“Special” groups are involved

» Parliam. representatives, medical doctors, attorneys, clergy › These are often privileged regarding evidence

Because it is against the company policy/immoral/…

» If the (suspected) behaviour is not illegal, it is much more difficult to investigate it legally!

Use your own staff for important investigations

» Use external independent experts (=third party!) Computer Forensics : Introduction 15

Who should/may use CF?

Authorization required for accessing data

» See privacy laws!

Live monitoring, hacking, password cracking etc. tools are legally "dangerous"!

» Possession alone might be criminal › Good explanation and evidence for its necessity/legal use might be

required!

Personnel to "do" CF:

» System administrators in their own area › With restrictions, additional permissions/consent/…!

» Experts for courts or private investigations › "Expert" is not a legal/protected name Anyone can use it!

» Everyone on their own system › Note: A second person (e.g. husband/wife) uses the system Consent by this person is necessary!


Evidence


“Evidence”

Circumstantial evidence (“Indiz”):

» A hint, which (alone or together with others) allows to conclude that a certain fact exists

Evidence (“Beweis”):

» A hypothetical situation is accepted as a fact by the judge (rarely: jurors) because he is convinced of it

› The circumstantial evidence is presumed to be true

» Types of evidence are often strictly regulated › Note: This is a legal distinction and has typically no influence on what can

be used as evidence. They are just treated differently.

Example: A witness is treated differently than objects

» Used to fulfil the burden of proof

In English the difference is more vague!

Computer forensics: We deal with circumstantial evidence, but normally its just called “evidence”!


Types of evidence

Who was it: Identifying information

» Typical data: IP addresses, login names, passwords › Language of the words used may also be interesting!

What was done: Traces of actions

» Typical data: Log files, shell history files, event log

» Especially important: Various application-internal logs and non-standard configurations

› The “standard” files are more likely to be cleaned by attackers!

What was added: Data itself

» Typical data: Additional program code, user accounts, program configurations

› Code: New/changed programs, modified source code

What was removed: Remains of data

» Typical data: Deleted files (destroyed data as well as his own “intermediate” files), encrypted files


Digital evidence

Digital evidence is

» Stored in computers: Disks, memory, … › Not: Printouts, fingerprints on DVDs etc.

» Being transmitted between computers: (W)LAN, E-Mails, … › Not: Voice telephone communication (but …!) etc.

Analogue evidence:

» Fingerprints, fibres, body fluids, physically damaged disk, …

Evidence requires interpretation.

» What does it mean that this Bit is “0”?

» An E-Mail header exists: Who added it? What does it mean?

» Requires a lot of tools: Are they working correctly?

» How many steps of interpretation are necessary?

» How reliable is the interpretation?

We will talk only about digital evidence in this course!


Basic problems of digital evidence

Everything can be manipulated – without any trace

» But how difficult is it in the concrete case? Any traces for this?

» What would have to be done/how long would it take?

» Digital data is typically not intended to be manipulation-proof › Exception: Digital signatures

› Hash values: Nice, but little use in this regard!

Main aspects in court:

» Time: Timestamps, logs etc.

» Authenticity: Is it "original" or manipulated? › Note: "Truthful" is something different altogether …

» Location: Where was the computer/PDA/phone at a time?

» Originator: Who was logged in/the author?

» Delivery: Did the "message" (E-Mail, phone, …) reach the recipient (and when; see above!)

› Note: Differentiation often necessary: Computer and human!


Where to find evidence

Disks: Hard disks, USB-Disks, SSDs, floppy disks, tapes, …

» The typical "storage medium"

» Note: These can be very small and very easily hidden › They might also pose as "normal" objects

Example: USB-Stick in pocket knife!

Devices: Mobile phones, PDAs, MP3 players, memory sticks, game consoles, toys (comp.-controlled), smart watches…

» Directly or in disks contained therein

» Also a storage medium; usually may contain arbitrary data › In addition to the "normal" data like music, contacts etc.!

“Recorders”: Cameras, audio recorders, GPS trackers, health monitors, TVs,…

» Similar to devices: Own data + any other stored data


Where to find evidence

Digital copiers/printers

» Might add a serial number to each copied/printed sheet!

» May contain old scanned pages

Media equipment: Media-PC, Internet-TV, satellite receivers, Internet-radio, harddisk recorders for TV etc.

» Often contain some storage element inside

» May contain history traces

» May contain unique identifiers for data stored online under a pseudonym (the identifier)

Generally: If there’s a CPU in it, it can store any data!

» Similar: If it has a USB socket, a network socket or a WLAN connection Must be investigated

› Bluetooth etc. Could contain data, check for abilities

» Only very rarely this is NOT the case!


A few examples of hidden storage…


Analysis of evidence

Various aims of analysis for evidence exist

» What is necessary depends on › Legal requirements (e.g. “possession” required)

› The questions to be answered

» Be careful to not be “steered” through defining very restrictive aims to a certain result!

All evidence should be

» Crosschecked

» Tied to suspect

» Explicitly define ambiguities or uncertainties


Analysis: Ownership of evidence

Was the suspect using the computer when the object was accessed, created, or modified?

Was the object located in an area created by the suspect?

Is the suspect the owner of the object?

» See file system permission!

Is the suspect solely responsible for the equipment containing the object?

Is the access to the equipment controlled by the suspect?

» Physically or through electronic means (access control, encryption etc)

SANS Institute: Forensic Plan Guide. http://computer-forensics.sans.org/ community/papers/gcfa/forensic-investigation-plan-cookbook_283


Analysis: Use of evidence

Has the suspect accessed, created or modified the object?

» Timestamps

» Sometimes: Which part of it?

Has the suspect been in direct contact with the object?

» Opening a document › “Did”

Has the suspect had indirect contact with the object?

» Access to directory with file & did view directory › “Could have done”



Analysis: Access of evidence

Does the suspect have the knowledge to be able to access, create, or modify the object?

» Books, Internet history, education, …

Does the suspect have the capabilities (tools) to be able to access, create, or modify the object?

» Slack space, steganography etc need SW to access

Has the suspect actually accessed the object and how?

» Timestamps, sending in mail, …



Analysis: Knowledge of evidence

Does the object possess any internal attributes that directly involve the suspect?

Is the object protected, obscured, or hidden by any means?

Is the object names similar to other object names the suspect has used?

Does the object contain words, terms, or phrases used by the suspect?

Does the object contain parts of images or things similar to the suspect?

Was the file password protected by a password known by the suspect?



Legal considerations

Computer forensic evidence should be

» Admissible: Don’t collect anything, which would not be allowed in court

› It is useless, and probably illegal too!

» Authentic: The evidence should be tied to the incident › Don’t go on fishing expeditions

» Complete: Not only the “damaging” parts, but all of it › Don’t suppress or ignore anything else

If in doubt, collect too much and ignore it later in evaluation!

» Reliable: Collection, handling, and evaluation should ensure veracity and authenticity

› See "Chain of Custody"!

» Believable: Should be believable and understandable in court › And for laymen too (accused, jury, …)

“The truth, the whole truth, and nothing but the truth”


Burden of proof

Note: Not an “obligation to prove"!

» You are not (legally) required to prove anything … unless you want to "win" the proceedings, of course!

» If something cannot be proven, this is disadvantageous for the party which bears the burden of proof

› False Obvious; Practically important: Unknown, no evidence/ witnesses, expert could not find anything conclusive…!

Typical basic rules:

» You state that something is true You have to prove this

» Civil procedures: Everybody proves what would be advantageous for them (and: must claim it; legal problem!)

» Criminal procedures State must prove everything!

» If the court is convinced (different levels in law!), the burden of proof switches to the other party to prove the opposite

Explicit deviations/special rules exist in many laws Computer Forensics : Introduction 31

Admissibility of evidence: General

Digital information is no evidence as such alone

» Illegal image on disk? How did it come to be there? Unknown! › Was it the accused, someone else through his account,

the police, a hacker who broke in over the network, … ?

› Additional information can help if present

Physical access to computer, logon-history, encryption etc.

One very important aspect (value, not admissibility as such!) is the person collecting and interpreting the evidence

» If this person is trusted no modifications took place later

» When a conclusion is stated as a fact, the person will not be very useful, as judges will not believe them

› Fact = Observable

Example: Free space on disk is 100 MB

› Conclusion = Fact + interpretation/general rules

Example: Windows will be slow (no swap file) and programs might crash if more space is required for log files/backups/…


Admissibility of evidence (1)

Continental law:

» Generally all evidence is admissible, regardless how obtained › Exclusions exist, but are few/very rarely apply!

› But what evidence is worth depends on

How it was collected and stored

By whom it was collected

Who analyzed it

How it was analyzed

Whether the conclusions are supported by facts

Whether the conclusions are "state of the art"

» Typically the judge (or rarely a jury) decides

Common law:

» Facts might also be fixed by parties! › If agreed upon, judge/jury cannot discuss it any more

» Esp. USA: "fruit of the poisonous tree" doctrine › Evidence obtained unlawfully may not be used


Admissibility of evidence (2)

Note: There is no "court-approved forensic SW"!

» Neither in the USA nor the EU/Austria there is a certification/approval for what "things"/"devices"/"SW" might/must be used for investigation

But: Investigation must be done according to “state of the art”!

» Employing the "usual" SW is typically state of the art

» Other software might also be used, but could require additional explanation in court

› Typically the case in the USA!

» Europe: Person of investigator is often more important › Officially certified court expert, reputation, experience etc.

› Method is only important if another expert criticizes it

Or the court knows/suspects from other cases that it might be suspect/wrong/incorrectly applied…


USA: The “Daubert” test

Evidence is admissible, if the reasoning or methodology underlying a test is scientifically valid and whether that reasoning/methodology properly can be applied to the facts

It consists of:

» The knowledge can or has been tested › “Does it work?”

» The theory/technique has been subjected to peer review and publication

› “Do at least some others think it is correct or not obviously incorrect?”

» The (potential) rate of error is known › “When/how often does it not work, what prerequisites exist?”

» The theory/technique has gained general acceptance in the relevant scientific discipline

› “Most others think/verified it is correct.”


The forensic process


The sequence of actions in CF (1)

Secure and isolate

» Remove all other personnel

» Keep reliable independent witness (police, other third party) › To protect against "The investigator added this data!"

Record the scene

» Photograph, write down › Example: Mouse on left or right side? Left-/Right-handed

› How are the systems connected (WLAN!)?

› What is the current state (running; screen content; …)

» In many cases there is quite a mess + lots of computers/devices/…

› You won't remember exactly where the disk was and whether it was powered (especially after some month/years)

Example: Disk behind desk? Fell down or deliberately hidden?

Example: Computer running Might act as a server

› Cabling might also be reconstructed, at least partially



Conduct a systematic search for data evidence

» All kinds of computers and storage mediums › E.g. steganography impossible without programs Disks, …

» Everything which has, even if only transient, data on it

Conduct a systematic search for non-data evidence › “Conventional" search, but important for data investigation

» Especially: Notes with passwords, hints for online services used, tokens, PIN/TAN/PUK

» Printouts in waste paper basket, …

» Stacks of empty storage media ("commercial distribution")

» Invoices for services (domain names, hosting, VPNs, …)

» One-time passwords/codes/payment (e.g. vouchers)

Start chain of custody

» “Bag & Tag”, here potentially before: Data duplication



Collect and package evidence

» Keep it safe (no loss/destruction) and secure (no changes) › Secure wrapping; external influences

› Magnetic media: Shielding against magnetic fields

Modern harddisks are quite resilient, but not all such media are as safe (e.g. magnetic stripe cards)!

› Flash cards, SSDs, USB sticks, etc.: Static electricity

› CD-ROM, DVD, …: Direct sunlight, high temperature

» Ideally: Make copies there and package & take both!

Interview persons with potentially important knowledge

» Encryption keys, passwords, location of further devices etc.

Maintain chain of custody

» Keep log on who has access and restrict this access



Inspect and evaluate data

» Perhaps triage: Immediate brief investigation › What to impound, already some illegal material found arrest

› “Triage”: Typ. sorting in three groups: Legal / Unknown / Illegal

» Detailed investigation in lab (from copy of media!)

» Create final report › What was done, what was found, what was not found, what should have

been found, how searched, confidence in results, …

Present the results

» In a report

» Potentially also before the court or some other group › Oral (cross-)examination probable

Potentially answer questions/respond to counter-expertises


Securing ev.: General considerations

Evidence must be secured in a "trustworthy" way

» Nobody should later be able to question the authenticity

Evidence should be collected as fast as possible, but without destroying anything

» This might mean keeping some devices powered, but others without power

› Supply with power: Mobile phones, PDAs, tablets, fax, …

› Store without power: Flash disks, hard drives, computers

» Disconnect any communication to/from the device Attention: Not necessarily immediately!

› E.g. mobile phones: Shielding (no powering off!)

› Computers: Network cables, phone lines, serial lines etc.

» Check with other forensic experts: Fingerprints › Obtaining traces may damage electronic media!


Securing evidence

Secure the scene

» Preserve potential fingerprints, ensure personnel safety

» Immediately restrict access to computers › Physically; electronically comes next!

» Document current state (hardware & software)

Secure the computer as Evidence

» If the computer is "OFF", do not turn it "ON" › Disconnect all power sources; unplug from wall AND computer

› Place evidence tape over each drive slot

› Photograph/diagram and label back of components with existing connections

› Label all connectors/cable ends to allow reassembly as needed

› Package components and transport/store components as "fragile"

› Keep away from magnets, radio transmitters, heated seats, etc.

Interview all persons/witnesses

Source: US Secret Service


Securing evidence: US Secret Service

» If the computer is "ON" › Stand-alone computer (non-networked)

Consult computer specialist

If specialist is not available

• Photograph screen

• Disconnect all power sources; unplug from wall AND computer

• Continue as with offline computer!

› Networked or business computers / Routers

Consult a computer specialist for further assistance, because pulling the plug could:

• Severely damage the system

• Disrupt legitimate business

• Create officer and department liability

» If the computer is "OFF“: Do not turn it on

Please note: Typical procedure for non-experts

» Experts will (try to) acquire the runtime-state first!

Scientific Working Group on Digital Evidence: Best Practices for Computer forensics http://www.oas.org/juridico/spanish/cyb_best_pract.pdf


Securing evidence: Live computers

Better: Obtain as much information from the running system as possible; only then "shutdown" the system

» General rule: Do not alter the state (On On, Off Off)!

1. Obtain a copy of the complete state

» Copy of the complete memory › With as little changes as possible!

Some additional software MUST be started for transfer!

» Output of various "state" commands, e.g. running processes, open network connections, open files/shares, …

2. Remove power cable from computer › Generally some files might be destroyed, so the computer might not boot

anymore. But much less data is lost/changed in this way than when shutting it down!

"Delete paging file on shutdown", "Clear privacy data when I close Firefox", …

» Not from wall socket: There might be a UPS somewhere!

» Laptops: Remove accumulator (both if present) as well Computer Forensics : Introduction 44

Pulling the plug – Or not?

Other recommendations are a bit more sophisticated

Servers: Shutdown

» Much data can be destroyed when a file/database/E-Mail server is "killed", which can be a problem for companies

› Data is lost, computer must be reinstalled/backups restored, …

› Could be problematic for investigation too: Garbled files, ToC, …

Especially all kinds of databases loose caches, need to be reconstructed etc.

» Little danger of deletion/modification scripts › These might be shut down at any point in time by someone else

(e.g. by UPS in case of power failure!)

» Hibernation is typically not available here

Appliances: Pull the plug

» Typically built to survive this without any problem/damage

» The runtime data must be copied before, of course! › Which might be very difficult or practically impossible anyway



Workstations: Pull plug / Hibernate

» Little damage to be done by killing it

» Usually full control by a single person Traps much likelier

» Restore much quicker and easier

» Affects only a single person, not a whole huge company!

» Problem: Modern OS use e.g. DB for storing their internal data › Pulling the plug might result in loss of much data

› Reduce the problem by letting the computer “rest”: Wait for some time (hard-drive activity dies) to make sure any open transactions have been persisted

Not foolproof – some DB will empty caches only if new data arrives

» If harddisk encryption is used, capturing the memory is the only chance of accessing the necessary key

› Encryption based on hardware (self-encrypting disk): Acquisition while still running is the only chance of obtaining any data at all!



Workstations: Pull plug / Hibernate

» Alternative (if available!): Hibernation › Little chance for destruction/traps, PLUS a full memory image!

Drawback: Previous hibernation file is overwritten (but which cannot be used to reconstruct a running system anyway!)

› But make sure this is not a shutdown/disabled

› In my opinion better than pulling the plug!

» Summary: 1) Copy memory

2) Copy all data from media

3a) Hibernate

3b) Pull plug


The order of volatility Registers, memory caches

Routing table, arp cache, kernel statistics

Established network connections, running processes

Memory

Opened file systems with encryption

Temporary file systems (Ramdisks)

Storage media in use

Remote data (on other systems)

Backup media: Disks not in use, tapes

WOM: CD-ROMs, DVDs

Evidence should be secured/collected in this order !

Separately: Analogue material » Physical configuration (cabling of devices; network topology), paper,

fingerprints, DNA, … Computer Forensics : Introduction 48

Practical sequence for a computer

Document system and actual time, ascertain privileges

Show active processes

» Plus environment, libraries, loaded modules, …

List current network configuration

» Established connection, listening sockets › Plus all data, e.g. which application they belong to

Copy of memory

» Complete or processes only, depending on possibility › Complete copy typically requires administrator login!

Duplicate swap space

» Could be deleted/modified during shutdown

Duplicate encrypted storage media

Stop system

Duplicate rest of storage media Computer Forensics : Introduction 49

Chain of Custody

Guaranteeing identity and integrity of the evidence

Requirements:

Making sure the piece of evidence on hand is the same as was taken from the suspect/scene of crime/….

› Serial numbers All harddisks/USB/… look exactly the same!

› “This is THE harddisk!”

Making sure there was no tampering with it › Witnesses of actions, trust in the person

› “The data on the harddisk has not been changed (while I had it)!”

Making sure the transition to the next custodian is logged › Who got it next, i.e. when was a chance for tampering

Lying around somewhere? Handed to an untrusted person? …

› “I am trustworthy, and the next user is it too!”

» Repetition of and until the presentation in court


Chain of Custody

Normally not that important:

» Falsifying a fingerprint on a clear plastic tape is difficult (replacement is easier, but also simpler to detect!), but modifying digital data is (techn.) trivial and leaves no traces!

But: Digital evidence has a very nice property here: Hash values can reliably prove "no tampering"!

» Acquire as early and trustworthy as possible: "Since then"! › I.e., we get an ABSOLUTE guarantee for no-tampering!

Not “He is trustworthy, so he didn’t change it”, but “It has objectively not been changed with very high probability”

» Store it "securely", e.g. on paper with signature of third person

» The “original” of data (not: medium!) is typically unimportant Only the content is relevant, so

› “Normal” chain of custody for the physical medium

› “Hash” for the data on it

And “normal” chain of custody for the hash printout!


Chain of Custody

You have to document

» Where, when, by whom was evidence discovered & collected › Plus: “Identity” of the evidence

Example: The harddisk with serial number s was found on desk x by person A at time t

» Where, when, by whom was evidence handled or examined › Plus: How it was examined

Example: Person A investigated it at time t with program P in lab L

» Who had custody of the evidence during what period › Plus: How was it stored then

Example: Person A stored it in the safe in the lab L at t1

» Changes of custody: When and how did the transfer occur Example: Person A gave it personally to person B at time t

Example: It was sent by registered mail from A to B at time t with package number y

Not everything needs to be on a single tag (especially 2.)!


Interviewing personnel/witnesses

Information to obtain:

» Owner

» User names, passwords › PW: Account, BIOS, E-Mail, configuration, network, ISP, applications, token

codes, …

» Procedures for access (log in method)

» E-Mail addresses, online services/applications used, ISP

» Purpose of the system, person(s) using it

» Security schemes (self-destruct systems; e.g. delete scripts)

» Offsite data: Backups, online replications, …

» Documentation of the system: Version numbers

» Existence & use: Encryption, Steganography!

Note also when information is not provided! › Or what turns out to be incorrect

» Won't help the investigation, but may be important in court Computer Forensics : Introduction 53

Gathering further useful information

Wastepaper baskets:

» Printouts of information

» Invoices, E-Mails: Hints to online services used

Backside of keyboards, drawers, post-its: Passwords/hints

Cables (esp. plugged in), chargers, packaging, manuals: Associated equipment

Packaging: Serial numbers, IMSI/IMEI, PIN, PUK

Other devices: Synchronization targets

Media: Stacks of empty media (type; commercial!)

Dust/no dust on connector sockets (USB, firewire, …)

Installed software (esp. “crapware”): Synchronization, backup, company-specific

Wireless networks: Some devices must create them


Guiding the search: Data on system

The aim of the search is most important

» Is it a search for "something illegal", a specific crime, or whether the image "xyz.jpg" is present on the computer?

» Uncovering all information that is recoverable is possible, but also a lot of work (and therefore extremely expensive!)!

Assessing the proficiency of the suspect

» What "hiding" can reasonably be expected? › If unknown, always assume the worst, i.e. expert techniques!

When to stop:

» If something matching has been found or must all, respectively most of, such data be recovered?

» Financial considerations (expenses)


The Heisenberg principle - Analogon

It is impossible to completely capture an entire running computer system at a single point in time from within

» Every kind of "copying the state" will change the state itself!

» Note: Virtualisation allows this; but this is “outside”!

The goal to reach:

» With as little changes as possible

» Without distortion (like installing additional software)

» Without bias (like adding hardware/software) › With additional hardware, the data state alone can be captured

completely and without modifications ( Theoretically!)

Decisions are necessary: what to do (& with what tools!)

» Generally: Obtain as much data as possible with fewest changes

» Trivial examples: Display running processes and photograph the output on screen

› Even better: Use your own (statically linked) program from a CD Computer Forensics : Introduction 56

Documenting the investigation

The following elements should be documented for each step of an investigation

» Start time

» Person investigating

» Description of the investigative step

» Reason for this step › What do we expect to gain from it?

» Tools and their version which are employed

» Parameters used for the tools

» Result of the analysis

» End time

» Ensure integrity of the results and the documentation › Hash values for all digital results

» Ensure authenticity and confidentiality: Sign & encrypt › Paper: Sign & lock away

» Archive the tools used


Documenting actions

All actions during an investigation must be documented

» This starts with acquiring the evidence! › Writing down and photographing when/how the computer was found,

which state it was in, etc.

Running systems: Every single command entered must be documented with the time and the complete results

» Ideally the log and the result should be stored as a file with a checksum to verify its integrity

Offline systems:

» The state must be exactly documented, e.g. checksums over the whole disk

» Every step of the examination should be documented like in a running system

Generally: Also document the tools (make, version…) used!


Documenting actions

Methods of documentation

» Pen & paper: For non-electronic actions › Disk is duplicated, computer is unplugged, …

» Other “analogue” documentation: Photos, audio commentary › Might be digital today, but are not the action itself

» Electronic log: If possible, e.g. protocol of all commands (and their output) issued during investigation

› Depends on the system/software used

Chain of custody: Important for the documentation too!

» Pen & Paper: Number pages, don’t leave partly empty, sign every page, separate signature for “end of document"

» Digital documentation: Photos, audio logs, … should contain metadata (e.g. time and serial number of camera) if possible


Documenting actions: “script”

The “script” command (*nix) copies the in- and output to a file

» Note: The commands should be only “normal” text commands › E.g. “vi” will not be represented correctly!

» End with Ctrl+D (or “exit”)

Example: “script –f log.txt” » Script started on Tue 05 Jul 2011 01:24:13 PM CEST

[root@mail backup]# date

Tue Jul 5 13:24:18 CEST 2011

[root@mail backup]# ls –al

total 36

drwxr-xr-x 3 root root 4096 Jul 5 13:24 .

drwxr-xr-x 25 root root 12288 May 17 21:49 ..

drwxr-xr-x 5 root root 4096 Jul 5 04:06 db

-rw-r--r-- 1 root root 0 Jul 5 13:24 log.txt

[root@mail backup]# exit

exit

Script done on Tue 05 Jul 2011 01:24:32 PM CEST

Don’t forget: Hash value, read-only, store on other disk, …! Computer Forensics : Introduction 60

Documenting time/time difference

Very important for the evaluation later

» Note: We can’t know the difference between the computer time and the real time at some point in the past: Only now!

Time on investigation system should be very precise

» Use NTP or similar for synchronisation (and take care of timezone and DST!)

Time on investigated system should NOT be changed!

» Only the difference should be documented

Practical problem: How to do this!

» Solution 1: Document time on investigated system and manually add (paper, not file!) the “real” time at that moment

» Solution 2: Connect both systems, redirect output to second system, call “date” on first system, note timestamp of created logfile (not the timestamp within it!) on second system


Crime Information needs


Information according to crimes

Electronic intrusion

» Configuration files

» Executable programs and source code/scripts

» Open ports, running processes (esp. servers)

» Logs: Activity, connection, programs, communication, …

Fraud

» Address books, calendars: Physical, E-Mail etc.

» Images: Cheques, currency, West. Union, signatures, products…

» Credit card data, esp. CVC

» Office documents: Letters, spreadsheets, databases

» Banking/accounting software: Dedicated and online

» Internet activity: Logs, caches, cookies, …

» Account information: eBay, banks, …

» Communication history: E-Mails, chat logs



Undesirable communication (threats, spam, mobbing)

» Address information: E-Mail, telephone, …

» Documents: Background information, diaries, legal etc.

» Communication: Letters, E-Mails, SMS, chat logs, …

» Internet activity: Cache, logs, cookies

» Accounts: Online communication facilities

» Images: Person, products, fakes

» Software: Mass mailers, text/image/PDF generators

» Financial information: Accounts, banking



Violence: Child abuse/pornography, domest. violence, death

» Images, especially hidden ones, and videos

» Date and time stamps

» Internet activity: Cache, logs, cookies, access time, searches

» Software: Communication, photo, P2P

» Address information and communication: E-Mails, chats, tel.

» Documents: Legal, medical



Identity theft

» Personal information: Name, address, credit card, …

» Communication: Especially copies of other person's, obtaining/buying information online

» Software: Generators (names, credit card numbers), imaging (scanner, photo modification)

» Images: Certificates, forms, signatures

» Documents: Forms, letters, orders, …

» Electronic signatures

» Internet activity: Cache, logs, searches



Copyright

» Software: P2P, CD/DVD-burning, encryption, recoding, key generators, cracks

» Documents: Serial numbers, authorization information

» Internet activity: Cache, logs, searches, cookies

» Images: Covers, license forms

» Communication information: E-Mail, chat

» Accounts: Web-Sites, FTP, shops



Information according to “crimes”

Pornography surfing, time-wasting, …

» Internet activity: Cache, logs, searches, cookies › Special problem: Streaming media. Only URL left; content might have

changed; security measures to prevent downloading, …

» Images: Undesirable content

» Communication information: Chat


» Logs: Firewall, Web-proxy

Administrator IT abuse

» Logs: Servers, firewalls, proxies, routers

» Data: Additional data stored somewhere

» Programs: New services (FTP, webserver, …)

» Databases: DBs


Signs for an attack


Common signs for an attack (1)

Additional users?

» All new accounts are suspicious: Why are they there? Who created them? Automatically through software installation?

» Administrative/high rights or any other special permissions?

» When were they created? Was the Administrator active/logged in at that point in time?

» Passwords modified (not: user changed and it doesn’t work)? › Or empty passwords?

» Additional permissions of existing users (promoted to admin)?

Additional processes?

» Might be hard to detect, as especially Windows runs many processes in the background for the OS itself.

» What are they doing: Network connections/listening?

» What executables are they based on?



Suspicious webserver data?

» Because a webserver is almost everywhere and typically accessible anonymously!

» Especially the error logs: Signs of attacks

» Especially the access logs: Scripts previously not executed/URLs not retrieved or not existing

» Signs for SQL injection, shellcode etc?

» Additional files/directories in the webserver location?

Security software alerts?

» IDS/IPS/firewall/… alerts (Attention: False positives!)?

» rkhunter, chkrootkit, …?

» Full antivirus scan shows something?



Log modifications?

» Logging deactivated (partially)?

» Missing log files/log archives?

» Temporal “holes” in log files (no entries for some time)

» Additional software installed/login events/…?

Temporary files?

» Anything new in /tmp, C:\Temp, C:\Windows\Temp, …which does not look like the normal files there?

» Linux: Any kind of source code?

» Windows: Executables/DLLs?

» Delete everything, reboot Still empty/expected files only?

Databases: injected data?

» Fulltext search for injected JavaScript, SQL code, HTML …?



Suspicious activities of users? › Depends heavily on what users are expected to do: Mail store only or

developing software?

» Linux (shell history!): sudo, nc, ssh, scp, ftp, telnet, ?sh, chmod, chown, useradd, ln, mkdir, …

» Windows: Downloaded executables, frequent logins/logouts, started programs, …

» Any other logins: SSH, sftp, WebDAV, …?

» Web applications: Who logged in when (esp. admin!)?

Indirectly: Software release state Updates available? » Any known unpatched security problems?


Problems of CF


Technical problems of CF

Anything done to a system changes it

» Especially problematic for running systems

» Usually less of a problem for hard disks › Reading data might change the content microscopically …

You can never trust the system under investigation

» It may be hacked, modified by the owner etc.

Proving you did not change anything is difficult

» You must be "above suspicion" & precautions Process!

The past can never be known

» We can only find hints what might have possibly been › The content could have been manufactured by someone!

› This can be pretty good evidence, but no absolute proof

Not everyone knows everything

» Every forensic examination is limited by the examiner!


Systematic problems of CF

Identifying the attacker: IP addresses are often the only traces of “hacking”; commonly they cannot be identified

» No information available anymore

» Used a proxy (=other hacked computer; commercial proxy service) without any logs on that one

Finding traces: If the attacker is good, once he has com-promised the system he can hide his tracks very well

» Note: It is very easy to forget something, but you can hide almost every trace!

› Exceptions: Already backed up, external systems (network sniffers/IDS on other system not yet hacked, …)

Note: Many investigations are successful

» E.g. child pornography is difficult to hide and still "use"

» Culprit may not even once forget to perform all security pre-cautions (when he does won't immediately notice this fact!)


Bias of the investigator

Very dangerous and must be reduced as far as possible

» To avoid it completely is probably impossible for a human …

Dangers:

» Limitation of investigation › “This can’t be found here”, “I’m sure this didn’t happen”, …

» Limitation of interpretation › You find a picture of a naked child: Is it child pornography in the legal

sense? Or just a picture of your newborn child?

» Limitation of certainty › “Obviously this was the reason”

Common: Confirming a theory Disproving a theory » Therefore: Explicitly look for things which would invalidate your

current assumption › E.g. "File was copied; if so, then MAC should…" Are they?


Distribution

Much data is not stored on "the" computer anymore

» Cloud Computing (e.g. Amazon Simple Storage Service; S3) › Need not be currently running

» Webmail accounts: Send mail to yourself, or create a draft

» “Online harddisks" › Example: RapidShare, Dropbox and similar services

» VPN networks to other systems › One more computer somewhere…

Obtaining a copy of one system is often not enough today!

» Find traces of the existence of remote information

» Find traces of the remote information itself › Caches, paging file, file slack, local copies, …

» Try to access this remote information › By seizure, copying, access over the network, …


(De-)Duplication

Data often exists in numerous copies

» Installation package and installed version

» Temporary files, old versions

» Quoted content (E-Mail sequences!)

» Full copies in different locations › E-Mail with CC/BCC, local file vs. stored on server (“Windows offline files”)

De-duplication can reduce the work/duration significantly

Potential problems:

» When is something a duplicate? › Is a quoted mail one? Or is this something different?

» Which is the “original” (if we care about this)?

» How to exclude the duplicates?

» How to keep the references to the duplicates?


Computer forensics vs. encryption

CF does work, but doesn't bring usable results if the data dis-/recovered is encrypted

» Depends strongly on the kind of encryption!

For some programs decryption software is readily available

» Especially the integrated encryption of MS Office and Zip!

» Sometimes based on weaknesses or short keys › But otherwise just brute force attacks: High computing power, special

software, and long time may be necessary!

» Sometimes passwords are not meant to be secure, but rather to prevent accidents (e.g. backup passwords)

Especially problematic: Hardware

» Tokens, self-encrypting harddisks, smartcards etc. › Extracting the key typically impossible or requires enormous amount of

effort


Computer forensics vs. encryption

If really good encryption is used, there is almost no chance of decryption without the key (or brute forcing the data)

» One of the reasons for hidden searches: Get at the data before/after it has been en-/decrypted!

» But: Very often passwords are known words ( lists!), are written down somewhere, stored in a safe, …

› Important to search the environment for any clues!

» See also the importance of copying the memory › Either the password is still present (very bad implementation) or at least

the cryptographic key (necessary to work)

» “Cryptographic containers” that are not in use Try to find traces of password/key or hashed passwords for cracking!

› Breaking password hashes is therefore an important part of CF

› Brute forcing the password has fair chances of being successful

Depends on the security of the password


Data hiding methods

Numerous approaches to hide data exist :

» Through the operating system › Mark as "hidden", "system", ...; use ADS; “dot-files”

» Renaming/Changing file extension : "order.txt" "cmd.com"

» RAM slack: End of file End of sector

» File slack: End of file end of cluster

» Partition slack: End of partition end of track

» Disk slack: End of last partition end of disk

» Unallocated/bad/reserved sectors

» Delete file/partition; format disk

» Steganography

» Encryption: Not really hidden, but “unusable” › But see: Hidden containers


Data hiding: Common problems

Several methods are "unstable“

» Later actions might (or will) destroy the data

Many approaches require special programs

» These must be stored somewhere

» “Manually” doing it is only very rarely possible

Hiding data still results in changes

» Two images: One before, one after

» “Explain the difference!” This is not part of a file, so why has some unused area on the disk changed?

If the method is known, its use might be easily proven

» Which then will need some explanation › “Knowledge of illegality”

Raw searches will trivially uncover it Encryption necessary


What is “Steganography”?

Steganography: Hiding messages within normal data

» The intention is that there is no sign that data exists at all

Typical "recipients": graphics, HTML, text, executables

» Common problem: Only a small part of content data can be used for hiding information Large "cover" for little "content"!

Areas of use:

» Where encryption is illegal

» When the fact of communication itself should be hidden

First encrypt, then employ steganography

» Makes detection through statistics much harder!

Relation to computer forensics:

» Hiding data in "inaccessible" places is steganography too

» Examples: Various slack spaces, alternate data streams › Rather easy to uncover, if presence is known!


Problems of Steganography

Not very resilient:

» Data hidden in images is easily destroyed through recoding

» Text can be reformatted

Not all base data is suitable:

» Many files are exactly "known": E.g. OS files cannot be used to hide data within them

› See also the problems caused by signed code!

Complicated to use: Additional tools necessary

» These can be found on the computer, disks, USB sticks, … › But need not necessarily be installed!

Large and seemingly important base material needed

» This is not always available or is a hint to hidden data

Requires a high level of knowledge to be "good"

» Free tools are available, but these are often easily detected!


CF vs. Steganography

In practice, Steganography seems to be rather rare

» There are much easier methods for hidden communication! › E.g. the personal ad columns with certain pre-defined texts

› If the text to hide is very long (or multiple pictures, videos), Steganography is problematic even today

Still, looking for hints that it has been applied should be part of every investigation

» Are there any traces of Steganography programs?

» Is there suspicious data?

Brute force attacks, e.g. using steganalysis programs on all images on a computer, are probably less useful

» Requires a long time and it is improbable to find anything › Mostly the programs only "support" specific tools for hiding!


Common errors


Common errors of a CF process (1)

No incident response plan

» At some time an incident will happen. If there are no plans what to do in which sequence, most probably the wrong things will be done!

» Requirements: › Who should be alarmed when

› Rules for escalation

› Guidelines for quickly assessing the problem

Without changing anything!

› Should be clearly documented and available without the system

I.e., ideally on paper!

Underestimation of the incident

» Third parties or other systems might also be affected › Example: Laptop was stolen Data on laptop is “gone”

But: Remote access to company servers possible?



Delayed detection of an incident or response to it

» E.g. the earlier the disks are copied, the more information will still be present

» Reduction of the time the attacker has for performing changes or hiding his tracks

› As soon as it is definite that an incident occurred “full alarm”!

› Keep any “preliminary” investigations for later & for experts

Management is informed late or incompletely

» External investigations might be costly: The management needs full information (as far as available)

» Responsible for business continuity/contingency measures outside of the IT area

» Decision on whether to involve the police or through whom

» Special measures might be necessary Must be authorized



Incomplete documentation of activities

» Chain of Custody (see above)

» But also for other (non-IT) measures › Might be extremely important in the legal area: Did you do everything (or:

enough) to reduce the damage? (Insurance!)

› Did you do enough to prevent damage to third parties? (Liability!)

» If no documentation exists, going to court might still be an option later (although with less valuable evidence)

Digital evidence is protected inadequately

» If the option for a court proceeding should remain open, very strict standards for access to data are necessary

› Checksums for everything!

» Evidence should be stored on read-only devices (today’s hard disk sizes typ. prevent this!), offline, and physically secured


Common practical mistakes (1)

Quickly entering some commands to find the problem

» This will change timestamps, add data, destroy data etc.

» These executables might have been modified by an attacker!

Using graphical tools

» This is no problem as such, but graphical tools require lots of libraries and typically do many things in addition (e.g. active desktop showing webpages, logging activities/MRU lists)

Killing suspicious processes

» As long as it is running, we might observe it and copy its RAM

Entering commands without a protocol

» We will later not be able to identify which results occurred as side-effects of the command we entered!

Installing addit. software (for recovery, investigation …)

» Destroys a lot of data, is potentially useless



Writing protocols on the disk under investigation

» Will again destroy data; potentially modified by malware

Waiting for the problem to solve itself

» Attackers are unlikely to go away on their own….

Immediately pulling the plug of everything in reach

» Documenting the current state and acquiring live data is typically preferable; losses in the meantime or probably small

Repairing the system/blocking connections on firewall/…

» It works again, but is the door for the intrusion closed?

» Tips off the intruder; some observation can be useful



Damaged devices/data is not documented as such

» If something is physically damaged Document (photo, log)

» If data turns out to be damaged: Document that (and when/how) this was identified

» Very important for potential liability: “The investigator destroyed/damaged it”

Some things are not that easy to decide Support of management for (afterwards decided as such!) incorrect decisions is necessary!


Report on investigations


Final report: General information

Identity of the examiner

Identification of the case, e.g. case numbers

» Who commissioned the report?

Subject of examination

» List of and serial numbers of disks/components/…

» Source of the equipment › Personally taken from suspect, received from police/court etc.

Procedural history

» When was what piece of evidence received, examined, passed on, reported upon, …

› Chain of custody!

» Description of examination: Who did what when in which way › Which techniques were used; state of the art?


Final report: General information

Results and conclusions

» Facts (see next slide): What was found

» Conclusions: What can be derived from that? › This must conform to a very high degree and state assumptions!

Example: Time of computer matches "real" time, file access date is 12.12.06 (facts) File was accessed at that time

• Note: Changing the clock, who used the computer, network connections, …?

› Includes a reliability assessment:

Not necessarily with a percentage, but should have it if possible!

"Might perhaps be", e.g. 10%

"Almost assuredly", e.g. 99,999%

» What was not investigated? › But might be interesting

› Reason for this "omission"

› What therefore cannot be deduced from the things investigated

› What could be in there and what could never (?) be in there


Final report: Content

Summary of findings (non-technical language!)

Detailed findings:

» Specific files matching the search › And other files supporting the findings

» String searches, keywords searches, and text string searches

» Internet-evidence: Web traffic analysis, chat logs, cache files, E-Mail, newsgroup activity, ICQ/Skype/… activity

» Graphic image analysis

» Ownership status of all files found › Who of the users owned them/when were they created/accessed

» Techniques used to hide data or limit access to it › Steganography, encryption, hidden attributes/partitions/streams

› Incorrect file names (e.g. JPEG files with ".bin" extension)

Annex: Printouts, digital copies, documentation


Confidence levels

Any conclusions should contain a reliability assessment

» There is always some uncertainty…

» But: Didn’t we want to find out the truth, the whole truth and nothing but the truth?

› Yes, but the world is imperfect (and money often limited !)

Informal categories:

» Possibly (Eventuell)

» Perhaps/Very possibly (Vielleicht)

» Probably (Wahrscheinlich)

» Most probably (Sehr wahrscheinlich)

» Almost definitely (Mit an Sicherheit grenzender Wahrscheinlichkeit)

» Definitely (Mit Sicherheit): This category is absent!


Computer Forensics : Introduction

Confidence levels: Casey’s C-Scale

Certainty level Description/Indicators Qualification

C0 Evidence contradicts “known” facts. Erroneous/Incorrect

C1 Evidence is highly questionable. Highly uncertain

C2 Only one source of evidence that is not protected

against tampering. Somewhat uncertain

C3 The source(s) of evidence are more difficult to

tamper with but there is not enough evidence to

support a firm conclusion or there are unexplained

inconsistencies in the available evidence.

Possible

C4 Evidence is protected against tampering or multiple

independent sources of evidence agree (which are

not protected against tampering).

Probable

C5 Agreement of evidence from multiple independent

sources that are protected against tampering.

However, small uncertainties exist (e.g. temporal

error, data loss).

Almost certain

C6 The evidence is tamper-proof and unquestionable.

No other explanation is possible at all. Certain

Casey, Eoghan: Digital Evidence and Computer Crime2, London 2004, 175 99


Examples: CF investigation guidelines

OLAF: European Anti-Fraud Office OLAF carries out external investigations. Part of the investigation procedure includes

collecting data, which can be in paper-based, digital or electronic format. The aim of this leaflet is to give basic information about OLAF's computer forensic procedure, which relates to the collection of digital or electronic data.

At the onset, OLAF will inform you of the purpose and the legal basis of the investigation and provide you with a copy of the Investigation Authority.

An experienced computer forensic examiner (CFE) using specialised tools will:

1. explain to you the steps involved and may request the assistance of your IT staff;

2. identify the data carriers/devices and take photographs to provide documentary evidence of their physical surroundings and layout;

3. produce an inventory of the hardware components which could hold the data, such as laptop or computer hard disks or external disks, hard disks of servers, back-up data carriers (tapes, DVDs, CDs etc), USB memory devices, external drives, pocket PCs, smart phone, analyses of network activity;

4. create a forensic disk image of the entire contents of the data carrier which becomes a "forensic evidence file", available if required for court or other proceedings. Each image has a unique "hash" value, which makes it possible to check if a copy is identical. The collected data will remain on the "forensic evidence file" and cannot physically be erased, or removed from the forensic log files. This ensures the integrity of the data and part imaging is not possible.

http://ec.europa.eu/anti_fraud/documents/forensics-leaflet/external_en.pdf 100


Examples: CF investigation guidelines 5. The CFE will ask you to sign the Computer Forensic Operation Report, which records each

step of the OLAF computer forensic procedure. This report forms part of OLAF's investigation file.

6. You will receive a copy of the report, which includes your rights as a data subject.

The forensic disk image is then registered and secured in OLAF's premises. The CFE works on a forensic working copy.

As part of the investigation process, OLAF examines the data in the forensic working copy in its secure forensic laboratory using specialised computer forensic software and hardware to make the searched data readable.

Automated processes and searches, for example by keywords, are used to identify case relevant data, which will be extracted and placed in the OLAF investigation file.

Your data will be stored for a maximum of 20 years after the end of the investigation and follow-up and then destroyed.

101 http://ec.europa.eu/anti_fraud/documents/forensics-leaflet/external_en.pdf

Examples: CF investigation guidelines

European Investment Bank Group (EIB) ….

3. Computer forensic procedures in case OLAF does not intervene

3.1 Setting of achievable objectives:

Conducting computer forensic operations and examinations is also an extremely labour intensive and resourceful job. Considering that complexity and the scarcity of forensic computing resources, choices needed to make such operations more efficient and more operationally effective, involve the following planning:

1. Be specific about the added value of a forensic operation. Where, how and when can forensic examiners assist this investigation? Is it necessary?

2. Set achievable objectives beforehand. Investigators should accurately outline the scope of the envisaged operation at the preparatory stage. During the operation, further selective data capturing may be necessary. Live data examination where possible may help target the scope of the operation.

3. Realise objectives set i.e. the operation must be feasible with the resources that are available.

4. Timely achievement of objectives set. Ensure that deadlines are met in time, to avoid jeopardising the whole operation e.g. expiry of the legal time limit.

5. Measure the outcome of a data acquisition or seizure e.g. that relevant material for and against the person was found and reference included in the final case report.

http://www.eib.org/attachments/strategies/anti_fraud_procedures_20130703_en.pdf Computer Forensics : Introduction 102

Conclusions

Obtaining some information from hard disks is easy

» Ensuring it is complete and usable in courts is difficult!

» There is only a single chance …

A wide variety of hard- and software exists, which must be treated differently and contains various information

» Specialization is needed for in-depth investigation

The huge amount of data is a problem

» Try to reduce the scope of investigation › Lists of "known good" files

» Automate examination › Keyword searches, deleted file recreation etc.

Expensive software needed

» Some investigation also possible with cheaper tools

» Open source software available partly


Thank you! Questions?

Thank you!

Any questions?

https://www.ins.jku.at


Michael Sonntag

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Literature

Casey, Eoghan: Digital Evidence and Computer Crime2, London 2004

NIJ Report: Forensic Examination of Digital Evidence: A Guide for Law Enforcement. http://www.ojp.usdoj/nij

NIJ Report: Electronic Crime Scene Investigation: A Guide for First Responders. http://www.ojp.usdoj/nij

dns: An introduction to: Computer Forensics http://www.dns.co.uk/NR/rdonlyres/5ED1542B-6AB5-4CCE-838D-D5F3A4494F46/0/ComputerForensics.pdf

RFC 3227: Guidelines for Evidence Collection and Archiving

Kuhlee/Völzow: Computer Forensik Hacks
