Digital Evidence Preservation | Decripte Security

Proper preservation of digital evidence is essential for successful forensic investigations and the legal admissibility of evidence in judicial proceedings.

Concept and Purpose

Digital evidence is information stored or transmitted in digital format that can be used as proof in investigations. It includes files, logs, emails, images, videos, network data, etc.

The purpose of preservation is to ensure that evidence is not altered, damaged or destroyed, maintaining its integrity and authenticity for forensic analysis and legal use.

Fundamental Principles

Integrity: Ensure that evidence remains unaltered from the moment of collection.

Authenticity: Confirm that evidence is what it claims to be and has not been tampered with.

Chain of Custody: Document every stage of evidence handling, from collection to presentation in court.

Competence: Perform collection and analysis with trained and qualified personnel.

Legal Compliance: Follow laws and regulations applicable to the collection and preservation of evidence.

Forensic Collection

Identification: Identify relevant sources of evidence (e.g., servers, workstations, mobile devices, removable media).

Acquisition: Create a forensic copy of the evidence using methods that preserve integrity (e.g., bit-by-bit disk imaging).

Write Blockers: Use write-blocker devices to prevent data from being written to the original media during acquisition.

Documentation: Record collection details (date, time, location, people involved, description of the evidence).

Hashing

Hash Calculation: Calculate a hash (e.g., MD5, SHA-256) of the original evidence and of the forensic copy to verify integrity.

Hash Comparison: Compare hashes to ensure that the copy is identical to the original and has not been altered.

Hash Record: Record hash values in the chain of custody.

Chain of Custody

Detailed Documentation: Record every transfer of custody of the evidence, including date, time, people involved and the purpose of the transfer.

Custody Form: Use a standardized form to document the chain of custody.

Signatures: Obtain signatures from everyone who handles the evidence.

Secure Storage: Store evidence in a secure location with controlled access.

Essential Tools

Write Blockers: Hardware or software devices that prevent writing to disks.

Imaging Tools: Software to create forensic images of disks (e.g., FTK Imager, EnCase).

Hashing Tools: Utilities to calculate hashes (e.g., HashCalc, md5sum).

Forensic Analysis Software: Platforms to analyze digital evidence (e.g., Autopsy, Volatility).

Storage Media

Hard Drives: Use new and formatted hard drives to store forensic copies.

Removable Media: Use removable media (e.g., DVDs, flash drives) only for data transfer, not for long-term storage.

Cloud Storage: Consider cloud storage for backup and redundancy, but ensure security and compliance.

Documentation

Incident Response Plan: Include evidence preservation procedures in the incident response plan.

Policies and Procedures: Create detailed policies and procedures for the collection and preservation of evidence.

Training: Train IT and security teams in forensic procedures.

Common Scenarios

System Intrusion: Preserve logs from servers, workstations and network devices.

Data Theft: Collect copies of files accessed and transferred illegally.

Internal Fraud: Preserve emails, documents and access records of suspect employees.

Malware Attacks: Analyze malware samples and infected systems.

Challenges

Encryption: Dealing with encrypted data requires knowledge of decryption techniques.

Data Volume: Large volumes of data require adequate tools and infrastructure.

Volatile Data: Collect volatile data (e.g., RAM memory) before it is lost.

Privacy: Balance the need to preserve evidence with privacy rights.