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Computer Forensics and Advanced Topics. Chapter 17. Computer Forensics. Application of computer science and engineering principles and practices to investigate unauthorized computer use and/or the use of a computer to support illegal activities

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Computer Forensics

  • Application of computer science and engineering principles and practices to investigate unauthorized computer use and/or the use of a computer to support illegal activities

  • Computer forensics is conducted for three purposes:

    • Investigating and analyzing computer systems as related to violation of laws.

    • Investigating and analyzing computer systems for compliance with an organization's policies.

    • Investigating computer systems that have been remotely attacked.


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Role of a Computer Forensic Specialist

  • Isolates security holes

  • Identifies modes of access

  • Detects clues for evidence of a cybercrime or security breach

  • Ensures maximum recovery of data and preservation of digital evidence


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The Forensic Process

  • Identify evidence

  • Collection of evidence

  • Examination of evidence

  • Analysis of evidence

  • Documenting and reporting of evidence


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Digital Evidence

  • Digital evidence can be retrieved from computers, cell phones, pagers, PDAs, digital cameras, and any device that has memory or storage.

  • Extremely volatile and susceptible to tampering

  • Often concealed like fingerprints

  • Sometimes time sensitive


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Digital Evidence

  • Evidence consists of documents, verbal statements, and material objects admissible in a court of law.

    • It is critical to convince management, juries, judges, or other authorities that some kind of violation has occurred.

  • If evidence will be used in court proceedings or actions that could be challenged legally, evidence must meet these three standards:

    • Sufficiency: The evidence must be convincing or measure up without question.

    • Competency: The evidence must be legally qualified and reliable.

    • Relevancy: The evidence must be material to the case or have a bearing on the matter at hand.


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Principles of Digital Evidence

  • Investigation/analysis performed on seized digital evidence should not change evidence in any form

  • Evidence should only be manipulated and analyzed on a copy of original source

  • Individual must be forensically competent to be given permission to access original digital evidence

  • Activity relating to seizure, access, storage, or transfer of digital evidence must be fully documented, preserved, and available for review


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Identify Evidence

  • Mark evidence properly as it is collected so that it can be identified as the particular piece of evidence gathered at the scene.

    • Label and store evidence properly.

    • Ensure that the labels cannot be removed easily.

    • Keep a logbook.

    • Identify each piece of evidence (in case the label is removed).


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Identify Evidence

  • The information should be specific enough for recollection later in the court.

    • Log other identifying marks, such as device make, model, serial number, and cable configuration or type.

    • Note any type of damage to the piece of evidence.

  • It is important to be methodical while identifying evidence.

    • Do not collect evidence by yourself—have a second person witness the actions.


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Identify Evidence

  • Protect evidence from electromagnetic or mechanical damage.

    • Ensure that the evidence is not tampered, damaged, or compromised by the procedures used during the investigation.

    • Do not damage evidence – Avoids liability problems later.

    • Protect evidence from extremes in heat and cold, humidity, water, magnetic fields, and vibration.

    • Use static-free evidence protection gloves, not standard latex gloves.

    • Seal the evidence in a proper container with evidence tape.


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Types of Evidence

  • Direct evidence is oral testimony that proves a specific fact, such as an eyewitness' statement.

  • Real evidence is physical evidence that links the suspect to the scene of a crime.

  • Documentary evidence is evidence in the form of business records, prints, and manuals.

  • Demonstrative evidence is used to aid the jury and can be in the form of a model, experiment, or chart, offered to prove that an event occurred.


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Three rules of Evidence

  • Best Evidence Rule

    • Courts prefer original evidence rather than a copy to ensure no alteration of the evidence has occurred.

  • Exclusionary Rule

    • The Fourth Amendment to the United States Constitution precludes illegal search and seizure and, therefore, any evidence collected in violation of the Fourth Amendment is not admissible as evidence.

  • Hearsay Rule

    • Hearsay is second-hand evidence—evidence not gathered from the personal knowledge of the witness.


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Guidelines for Collecting Evidence

  • While conducting the investigation, analyze computer storage carefully.

    • Analyze a copy of the system and not the original system – that is evidence.

    • Use a system specially designed for forensics examination.

  • Conduct analysis in a controlled environment with:

    • Strong physical security

    • Minimal traffic

    • Controlled access


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Guidelines for Collecting Evidence

  • Unless there are specific tools to take forensic images under Windows, DOS should be used for imaging process instead of standard Windows.

  • Boot it from a floppy disk or a CD, and have only the minimal amount of software installed to preclude propagation of a virus or the inadvertent execution of a Trojan horse or other malicious program.

  • Windows can then be used to examine copies of the system.


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Collecting Evidence

  • Each investigation is different. Given below is an example of a comprehensive investigation.

    • Remove or image only one component at a time.

    • Remove the hard disk and label it – use an anti-static or static-dissipative wristband and mat before beginning the investigation.

    • Identify the disk type (IDE, SCSI, or other type). Log the disk capacity, cylinders, heads, and sectors.

    • Image the disk with a bit-level copy, sector by sector – this will retain deleted files, unallocated clusters, and slack space.


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Collection Steps

  • Make a list of all systems, software, and data involved, as well as evidence to be collected

  • Establish criteria for what is likely to be relevant and admissible in court

  • Remove external factors that may cause accidental modification of file system or system state

  • Perform quick analysis of external logs and IDS output

continued…


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Collection Steps

  • Proceed from more volatile assets to less

    • Memory

    • Registry, routing table, arp cache, process cache

    • Network connections

    • Temporary files

    • Disk or storage device

  • Check processes running on the system

  • Copy arp cache, routing table, registry, status of network connections

  • Capture temporary files

  • Make byte-by-byte copy of entire media

  • Remove and store original media in a secure location

  • Do not run programs that modify files or their access times

  • Do not shutdown until the most volatile evidence has been collected

  • Do not trust programs on the system

  • Document the procedure


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Chain of Custody

  • The chain of custody accounts for all persons who handled or had access to the evidence.

  • It shows who obtained the evidence, when and where it was obtained, where it was stored, and who had control or possession of the evidence.


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Chain of Custody

  • Steps in the chain of custody are:

    • Record each item collected as evidence.

    • Record who collected the evidence along with the date and time.

    • Document a description of the evidence.

    • Put the evidence in containers and tag the containers with the case number the name of the person who collected it, and the date and time.


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Chain of Custody

  • Steps in the chain of custody are (continued):

    • Record all message digest (hash) values in the documentation.

    • Securely transport the evidence to a protected storage facility.

    • Obtain a signature from the person who accepts the evidence at this storage facility.

    • Provide controls to prevent access to and compromise of the evidence while it is being stored.

    • Securely transport it to the court for proceedings.


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Free Space vs Slack Space

  • When a user deletes a file, the file is not actually deleted.

  • Instead, a pointer in a file allocation table is deleted.

  • A second file that is saved in the same area does not occupy as many sectors as the first file – there will be a fragment of the original file.

  • The sector that holds the fragment of this file is referred to as free space because the operating system marks it usable when needed.

    • When the operating system stores something else in this sector, it is referred to as allocated.

  • Unallocated sectors still contain the original data until the operating system overwrites them.


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Free Spack vs Slack Space

  • When a file is saved to a storage media, the operating system allocates space in blocks of a predefined size, called sectors.

  • The size of all sectors is the same on a given system or hard drive.

  • Even if a file contains only 10 characters, the operating system will allocate a full sector of say 1,024 bytes—the space left over in the sector is slack space.


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Free Space vs Slack Space

  • It is possible for a user to hide malicious code, tools, or clues in slack space, as well as in the free space.

  • Slack space from files that previously occupied that same physical sector on the drive may contain information.

  • Therefore, an investigator should review slack space using utilities that can display the information stored in these areas.


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Education and Training

  • One of the most cost-effective tools in computer security

  • Knowledge of systems documentation

  • Knowledge of security procedures

  • Availability of resources and references

  • “Loose lips sink ships”

  • Clearly delineate information that may never be divulged over the phone


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Education and Training

  • Require proof of positive identity

  • Purpose of training and awareness program

  • Agency security appointments and contacts

  • Contacts and action in the event of a real or suspected security incident

  • Legitimate use of system accounts

  • Access and control of system media

continued…


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Education and Training

  • Destruction and sanitization of media and hard copies

  • Security of system accounts (including sharing of passwords)

  • Authorization for applications, databases, and data

  • Use of the Internet, the Web, and e-mail


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