Evidence handling and chain of custody

Evidence Handling and Chain of Custody – SSCP Exam Guide

Why Is Evidence Handling and Chain of Custody Important?

Evidence handling and chain of custody are critical components of incident response and recovery. In the event of a security breach, cyberattack, or any incident that may lead to legal proceedings, the integrity of collected evidence determines whether it will be admissible in court. Poor evidence handling can render months of investigation useless, allow perpetrators to escape prosecution, and expose the organization to legal liability. For security professionals, understanding these procedures is essential to protecting both the organization and the legal process.

What Is Evidence Handling?

Evidence handling refers to the proper collection, preservation, analysis, and presentation of digital and physical evidence during and after a security incident. It ensures that evidence maintains its integrity, authenticity, and reliability throughout the investigation lifecycle.

Key types of evidence in cybersecurity include:
- Digital evidence: Log files, hard drive images, memory dumps, network traffic captures, emails, database records
- Physical evidence: Hardware devices, printed documents, storage media (USB drives, CDs)
- Volatile evidence: Data stored in RAM, running processes, network connections, logged-in users (this data is lost when the system is powered off)
- Non-volatile evidence: Data stored on hard drives, flash storage, and other persistent media

What Is Chain of Custody?

The chain of custody is a documented, unbroken trail that records the seizure, custody, control, transfer, analysis, and disposition of evidence. It answers the fundamental questions: Who had the evidence? When did they have it? What did they do with it? Where was it stored?

A proper chain of custody document typically includes:
- Description of the evidence (type, serial number, unique identifiers)
- Date and time of collection
- Name and signature of the person collecting the evidence
- Each transfer of the evidence (from whom, to whom, date, time, purpose)
- Storage location and conditions
- Actions performed on the evidence (e.g., forensic imaging)
- Final disposition of the evidence

How Does Evidence Handling Work in Practice?

Step 1: Identification
Determine what constitutes potential evidence at the scene. Identify all devices, logs, and artifacts relevant to the incident.

Step 2: Collection
Collect evidence using forensically sound methods. For digital evidence, this means creating bit-for-bit forensic images (exact copies) of storage media rather than working on originals. Volatile evidence must be collected first because it disappears when systems are shut down. This follows the Order of Volatility:
1. CPU registers and cache
2. RAM (system memory)
3. Network state and connections
4. Running processes
5. Disk storage
6. Remote logging and monitoring data
7. Archival media

Step 3: Preservation
Protect evidence from alteration, damage, or destruction. Use write blockers when accessing storage media. Store evidence in anti-static bags, sealed containers, or secure evidence lockers. Maintain environmental controls to prevent degradation.

Step 4: Documentation
Document everything meticulously. Photograph the scene, label all evidence, record timestamps, and maintain the chain of custody form. Every person who touches the evidence must be logged.

Step 5: Analysis
Perform analysis on forensic copies only, never on original evidence. Use validated forensic tools. Generate cryptographic hashes (MD5, SHA-1, SHA-256) of the original evidence and compare them with hashes of the copies to verify integrity.

Step 6: Presentation
Present findings in a clear, objective manner suitable for legal proceedings or management review. Maintain all documentation to demonstrate the evidence was handled properly throughout.

Key Principles to Remember

- Integrity: Evidence must not be altered. Use hashing to verify integrity at every stage.
- Authenticity: You must be able to prove that the evidence is genuine and has not been tampered with.
- Completeness: Collect all relevant evidence; partial evidence can be challenged in court.
- Admissibility: Evidence must meet legal standards to be accepted in court. This requires proper chain of custody and handling procedures.
- Minimal handling: Limit the number of people who handle evidence to reduce the risk of contamination or challenges to admissibility.
- Forensic imaging: Always work on copies. The original evidence should be preserved in its original state.

Legal Considerations

- Evidence collected in violation of laws or organizational policies may be inadmissible.
- The best evidence rule states that original evidence is preferred over copies, though forensic copies with verified hashes are generally accepted for digital evidence.
- Hearsay rules may apply to computer-generated records, though many jurisdictions have exceptions for business records generated in the normal course of operations.
- Organizations should have pre-established policies and trained first responders to ensure proper evidence handling during an incident.

Roles Involved in Evidence Handling

- First Responder: The first person on the scene; responsible for securing the area and beginning evidence preservation.
- Incident Response Team: Coordinates the overall response and evidence collection effort.
- Forensic Analyst: Conducts detailed analysis of collected evidence using specialized tools and techniques.
- Legal Counsel: Advises on legal requirements for evidence handling and admissibility.
- Law Enforcement: May take over evidence collection in criminal cases.

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Exam Tips: Answering Questions on Evidence Handling and Chain of Custody

1. Order of Volatility is a favorite exam topic. Remember that the most volatile evidence (CPU registers, cache, RAM) must be collected first, before less volatile evidence (hard drives, archival media). If a question asks what to collect first, always choose the most volatile option.

2. Never analyze original evidence. If a question presents a scenario where someone is working on original media, that is almost always the wrong answer. Forensic copies should be created and analyzed instead.

3. Hashing is essential for integrity verification. Questions about proving evidence has not been tampered with will point to cryptographic hashes (MD5, SHA-1, SHA-256) as the answer. Hashes are generated at the time of collection and compared later to ensure no changes occurred.

4. Chain of custody questions focus on documentation. The correct answer will emphasize logging every transfer, every person who handled the evidence, timestamps, and maintaining an unbroken record. A break in the chain of custody can make evidence inadmissible.

5. Write blockers prevent modification. When the exam asks how to prevent accidental modification of a hard drive during forensic acquisition, the answer is to use a write blocker.

6. Know the difference between criminal and civil proceedings. Criminal cases require evidence to meet the beyond a reasonable doubt standard, while civil cases use preponderance of evidence. This affects how carefully evidence must be handled.

7. Look for the most legally defensible answer. When in doubt, choose the option that best protects the integrity, authenticity, and admissibility of the evidence. The answer that includes proper documentation, forensic imaging, and chain of custody is almost always correct.

8. First responder actions matter. If a question asks what a first responder should do upon discovering an incident, prioritize securing the scene and preserving volatile evidence over other actions like rebooting systems or running antivirus scans.

9. Do not power off a running system if you need volatile data. Shutting down a system destroys RAM contents, running processes, and network connections. Conversely, if the system is already off, do not power it on, as this can alter data on the storage media.

10. Understand that policy and procedures should be established before an incident occurs. Questions may test whether you know that organizations should have incident response plans, evidence handling procedures, and trained personnel ready in advance, not created ad hoc during an incident.