What Is Digital Forensics

Digital forensics is the collective term for techniques and methods used to collect, preserve, analyze, and report digital data from computers and networks as legally valid evidence. It is used in a wide range of scenarios, including cybercrime investigations, root cause analysis in incident response, and submission of electronic evidence in litigation (eDiscovery).

Forensic investigation targets include hard disks, SSDs, memory, network traffic, mobile devices, cloud environments, and IoT devices. Through recovering deleted files, analyzing metadata, reconstructing timelines, and analyzing malware behavior, investigators determine "what happened, when, by whom, and how."

The defining characteristic of digital forensics is that investigations proceed while maintaining evidence integrity. If it cannot be proven that evidence has not been tampered with, it loses its legal admissibility.

The 4 Steps of a Forensic Investigation

The digital forensics investigation process consists of four internationally recognized steps.

1. Collection: Identify and collect digital data that serves as evidence. Create bit-for-bit disk images (forensic images) and capture memory dumps. The most important consideration at this stage is to collect volatile data first, such as memory, network connections, and running processes.

2. Preservation: To guarantee the integrity of collected evidence, compute and record hash values (SHA-256, etc.). All subsequent analysis is performed on copies only; the originals are never modified. Document the Chain of Custody to make the evidence handling history traceable.

3. Analysis: Analyze preserved data using specialized tools. This includes file system analysis, deleted file recovery, registry examination, log correlation analysis, and timeline reconstruction.

4. Reporting: Compile investigation results into a report that is understandable to non-technical audiences. Clearly document findings, analysis methods, tools used, and conclusions. When used in legal proceedings, the evidence handling process must also be recorded in detail.

Key Analysis Techniques and Targets

Disk Forensics: Analyze all sectors of storage to examine file system structure, deleted files, data in unallocated areas, and file timestamps. File carving techniques can recover data even when file system management information has been lost.

Memory Forensics: Analyze RAM contents to identify running processes, network connections, encryption keys, and malware code. This technique is essential for detecting fileless malware that leaves no traces on disk.

Network Forensics: Analyze packet captures and flow data to identify unauthorized communications, data exfiltration, and communication with C2 (Command and Control) servers. Correlation analysis with SIEM logs is also important.

Cloud Forensics: A unique challenge in cloud environments is the restricted access to physical storage. Investigations focus on cloud provider API logs, access logs, and audit logs. In data breach investigations, IAM configuration change history and resource access patterns are key clues.

Legal Requirements and Considerations for Forensic Investigations

Using digital forensics investigation results in legal proceedings requires strict procedures to ensure evidence reliability.

Evidence Integrity: Prove that evidence has not been altered since collection by verifying hash values. If hash values do not match before and after analysis, the evidence's reliability is compromised.

Chain of Custody: Record chronologically who handled the evidence, when, and how. Both parties sign upon evidence transfer to guarantee continuity of custody.

Reproducibility: A third party must be able to obtain the same results using the same methods and tools. Record the tool versions, configurations, and procedures used in detail.

When a CSIRT conducts forensic investigations as part of incident response, always keep in mind the possibility of legal proceedings and follow evidence preservation procedures from the initial response stage. Inadequate evidence preservation may result in evidence being deemed inadmissible if legal action is pursued later.

To learn more about this topic, see What to Do After a Data Breach: A Step-by-Step Response Guide.

Common Misconceptions

Deleted files cannot be recovered even with forensic investigation: Even after files are deleted, the actual data often remains on storage and can be recovered with forensic tools. However, recovery becomes difficult when SSD TRIM functions or secure erasure processes have been executed.
Forensic investigations are only used in criminal investigations: Digital forensics is used not only in criminal investigations but also in corporate incident response, internal fraud investigations, submission of electronic evidence in litigation, and compliance audits.

Digital Forensics