Digital Forensics Essentials: Preservation, Acquisition, and Analysis
Digital Forensics Essentials (DFE) tests a defensible process for identifying, preserving, acquiring, examining, analyzing, and reporting digital evidence. The exam stresses order of volatility, chain of custody, hashing, write blockers, forensic imaging, timeline reconstruction, and the difference between live and dead analysis.
Core rules and concepts
- Forensic process: identification, preservation, acquisition, examination, analysis, and reporting. Each stage must be documented so another examiner can evaluate or reproduce the work.
- Order of volatility: collect the most perishable evidence first, such as CPU registers, cache, RAM, network connections, and running processes, before shutting down or imaging disks. Persistent media follows.
- Chain of custody: record who collected, handled, transferred, and stored each item, with dates, times, locations, and signatures. A break can undermine admissibility.
- Acquisition integrity: use a write blocker for dead-box disk acquisition, create a forensic image rather than working on the original, and hash before and after acquisition. Matching hashes support integrity, not guilt or innocence.
- Live vs. dead analysis: live analysis captures volatile state but changes the system; dead analysis is more controlled but loses volatile data. Choose according to authority, urgency, and investigative questions.
- Analysis: build timelines, correlate file system, log, browser, registry, and network artifacts, and distinguish user activity from system or malware activity.
- Reporting: state findings, limitations, methods, and supporting evidence; avoid overstating what an artifact proves.
Worked example
A compromised laptop is still running. The examiner documents the scene, photographs the screen, and captures volatile data such as RAM, network connections, and logged-in users according to policy. They then isolate the device from the network without powering it off unnecessarily. The disk is removed or connected through a write blocker, imaged, and hashed. The original is sealed and logged; analysis is performed on a verified copy. The reasoning follows order of volatility: volatile state disappears on shutdown, while disk data persists. Hashing and chain-of-custody records let others verify that the analyzed image matches what was acquired.
Traps that cost marks
Do not boot or run utilities from the original disk when a forensic image is required. Do not confuse a backup with a forensic image; backups may omit deleted space, metadata, or hashes. Do not skip hashing or chain-of-custody documentation. Do not assume one artifact proves intent: a file timestamp can reflect system activity, time-zone handling, or anti-forensic manipulation. Do not let live-response actions overwrite the very evidence needed for later analysis.