a post for students in my network security course
In the intricate landscape of cybersecurity, understanding “what happened” after a security incident is as crucial as preventing it. This is where forensic investigations come into play. Often a critical component of incident response, forensic analysis is the meticulous process of examining systems, devices, or networks to uncover the truth about an event, whether it’s a cyberattack, an internal policy violation, or simply an unexpected system behavior. Cybersecurity analysts leverage specialized skills and tools to build a comprehensive picture of what occurred.
Building Your Digital Detective Kit
Embarking on a forensic investigation requires a carefully assembled toolkit designed to collect and preserve digital evidence without altering it. At the core of this capability is a digital forensics workstation, a dedicated and secure environment for analysis.
Key hardware components of a forensic kit include specialized write blockers, such as a Tableau SATA- and IDE-capable hardware write blocker. These devices are essential because they prevent any accidental or intentional modifications to the original storage media during the investigation, ensuring the integrity of the evidence. Along with write blockers, a kit would contain various cables, drive adapters, and wiped removable media for storing collected data. For physical scene documentation, cameras, crime tape, and tamper-proof seals are also part of the toolkit. Critical administrative items like documentation forms, chain of custody forms, incident response plans, incident forms, and call lists are also vital for proper procedure and legal defensibility.
The Core of the Investigation: Imaging and Analysis
Once the physical setup is ready, the first and most crucial technical step is creating a forensic disk image. This isn’t a simple file copy; it’s a bitwise, or “forensic,” image, meaning it’s an exact, sector-by-sector copy of the original drive, preserving every piece of data, including deleted files and slack space. Tools like dd, FTK (Forensic Toolkit), and EnCase are commonly used for this purpose. It’s important to note that standard copying utilities like xcopy are not suitable for forensic imaging as they cannot create a bitwise image.
To ensure the integrity of the collected evidence, hashing utilities like MD5sum and SHAsum are used. Hashing creates a unique digital fingerprint of the data. If even a single bit of the original data is changed, its hash will be different, immediately indicating tampering or corruption.
During data collection, investigators follow the order of volatility, meaning they collect the most volatile data (data that is most likely to disappear quickly, like RAM contents) first, before moving to less volatile sources like hard drives.
After imaging and hashing, the real analysis begins, often using powerful forensic investigation suites such as EnCase, FTK, Helix, Sysinternals, and Cellebrite6. These suites provide a wide array of analysis utilities2, including:
- OS and process analysis—Examining operating system logs, running processes, and system configurations to identify malicious activity or unauthorized changes.
- Mobile device forensics—Specialized tools and techniques for extracting data from smartphones and tablets.
- Password crackers—Tools like John the Ripper and Cain & Abel can be used to recover passwords from hashed or encrypted formats, potentially providing access to encrypted files or systems.
- Cryptography tools—For dealing with encrypted data found on systems.
- Log viewers—To parse and analyze various system and application logs for suspicious entries.
Investigators also specifically look into slack space, which is the unused space left at the end of a file’s last cluster when it’s written to a drive. This space often contains remnants or “file fragments” from previously deleted files, offering a trove of potential evidence. Through these analysis methods, investigators can unearth various types of data, from extracted emails and web search histories to iCloud setup logs with timestamps, and even remnant data from system cleaners like CCleaner, or specific document types like resignation letters.
The Unbreakable Chain
Throughout the entire process, maintaining a meticulous chain of custody is paramount. This formal process documents every person who has handled the evidence, when they handled it, and what they did with it. A broken chain of custody can compromise the admissibility of evidence in legal proceedings, undermining the entire investigation.
Forensic investigations are a cornerstone of robust cybersecurity. They provide the deep understanding needed to recover from incidents, refine security defenses, and hold responsible parties accountable. By systematically gathering and analyzing digital artifacts, cybersecurity professionals can uncover the digital truth, one byte at a time.