The Basics of Digital Forensics

1. Digital Forensics: Science Applied to Law

Simply put, forensics is the application of science to solve a legal problem.

Law and Science. Digital forensics is the application of computer science and investigative procedures for legal purposes. It's not just about the technology; it's about how that technology intersects with the legal system. The best scientific evidence is worthless if it's inadmissible in court.

Uses of Digital Forensics. Digital forensics is used in criminal investigations (child pornography, identity theft, homicide), civil litigation (eDiscovery), intelligence gathering (DOMEX), and administrative matters (policy violations). The BTK killer case demonstrates how metadata from a floppy disk led to the capture of a serial killer after 30 years.

Organizations and Standards. Several organizations contribute to the discipline, including the Scientific Working Group on Digital Evidence (SWGDE), the American Academy of Forensic Sciences (AAFS), the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB), and the National Institute of Standards and Technology (NIST). These organizations help establish protocols, standards, and procedures.

2. Understanding Technical Concepts is Foundational

Intimate knowledge of the inner workings of a computer is critical for the digital forensics practitioner.

Bits and Bytes. Computers use binary code (1s and 0s) to store data. Eight bits make a byte, which represents a character. Hexadecimal is a base-16 shorthand for binary. ASCII and Unicode are encoding schemes that convert binary into human-readable text.

Storage and Memory. Data are stored magnetically (hard drives), electrically (flash memory), or optically (CDs, DVDs). Memory (RAM) is volatile, meaning data disappear when power is removed. Storage (hard drives, SSDs) is non-volatile. Flash memory is used in thumb drives and SSDs.

File Systems. File systems (FAT, NTFS, HFS+) track the location of files and free space on a drive. Understanding allocated (used) and unallocated (free) space is crucial for data recovery. Slack space contains fragments of previously deleted files.

3. Labs and Tools Ensure Reliable Forensic Results

Quality assurance is a bedrock principle that underpins every discipline in forensic science.

Forensic Labs. Forensic labs are typically run by law enforcement agencies. The FBI's Regional Computer Forensic Laboratory (RCFL) program provides services and training to law enforcement. Virtual labs are also emerging, but security and connectivity are major concerns.

Quality Assurance. Quality assurance (QA) programs ensure the accuracy and reliability of analytical results. This includes technical and administrative reviews, proficiency testing, and tool validation. The Glen Woodall case highlights the need for quality assurance.

Tools and Documentation. Digital forensic tools include hardware (write blockers, cloning devices) and software (FTK, EnCase). Documentation is critical, including submission forms, chain of custody records, examiner's notes, and final reports.

4. Evidence Collection: Preserve, Document, and Chain

How the digital evidence is handled will play a major role in getting that evidence admitted into court.

Crime Scene. Securing the scene is the first priority. This includes isolating computers and wireless devices from networks to prevent remote access or data wiping. Removable media (DVDs, thumb drives, memory cards) should be located and secured.

Documentation. Documenting the scene involves detailed notes, photographs, and video recordings. The order of volatility dictates which evidence to collect first, starting with the most volatile (RAM) and ending with the least (archival media).

Chain of Custody. A well-documented chain of custody is essential for admissibility. Evidence must be marked, sealed, and tracked from collection to court. Forensic cloning creates an exact copy of the hard drive for analysis, preserving the original evidence.

5. Windows Artifacts: Clues Left Behind

Your computer will betray you.

Deleted Data. Deleted files are not truly erased; they remain on the hard drive until overwritten. File carving can recover files from unallocated space. The hibernation file (Hiberfile.sys) stores data from RAM when a computer enters hibernation mode.

Windows Registry. The Windows Registry is a database of system and user settings. It contains valuable information, such as installed programs, recently opened files, and USB device history. The USBStor key in the registry can show when external drives were connected.

Other Artifacts. Other Windows artifacts include print spooling files, Recycle Bin contents, metadata, thumbnail caches, Most Recently Used (MRU) lists, restore points, shadow copies, prefetch files, and link files. Each of these can provide clues about user activity.

6. Antiforensics: Hiding and Destroying Data

Each betrayal begins with trust.

Encryption. Encryption converts data into an unreadable format (cipher text). It's used to protect sensitive information, but can also be used to hide criminal activity. Common encryption tools include BitLocker, FileVault, and TrueCrypt.

Password Attacks. Passwords can be cracked using brute force attacks (trying every possible combination) or dictionary attacks (using common words and phrases). The key space (length of the key) determines the difficulty of breaking encryption.

Data Destruction. Data can be hidden using steganography (embedding messages within other files). Data can be destroyed using drive-wiping utilities, but these tools can leave telltale signs of their use.

7. Legal Authority: The Foundation of Digital Forensics

Although a “forensic” science, the legal aspects of digital forensics can't be divorced from the technical.

Fourth Amendment. The Fourth Amendment protects against unreasonable searches and seizures. A search warrant is required unless an exception applies (consent, exigent circumstances, plain view). The Electronic Communications Privacy Act (ECPA) protects electronic communications.

Electronic Discovery. Electronic discovery (eDiscovery) involves identifying, preserving, collecting, and producing electronically stored information (ESI) in civil cases. The duty to preserve data begins when litigation is reasonably anticipated.

Expert Testimony. Digital forensic examiners often serve as expert witnesses. They must be qualified based on their knowledge, skill, training, or experience. The Daubert standard governs the admissibility of expert testimony.

8. Internet and Email: A Treasure Trove of Evidence

Social networks, e-mail, chat logs, and Internet history represent some of the best evidence we can find on a computer.

Internet Overview. The Internet uses TCP/IP, HTTP, and DNS to deliver web pages. A URL (Uniform Resource Locator) identifies a web address. Web pages can be static or dynamic. Peer-to-peer (P2P) networks facilitate file sharing.

Web Browsers. Web browsers (Internet Explorer, Firefox, Chrome) create artifacts such as cookies, temporary Internet files (cache), and browsing history. The INDEX.DAT file tracks browsing activity in Internet Explorer.

Email. Email uses protocols such as SMTP, POP, and IMAP. Email headers provide a record of the message's path. Email can be spoofed or remailed anonymously.

9. Network Forensics: Tracing the Attack

We can find a network almost anywhere, from small home networks to huge corporate ones.

Network Fundamentals. Networks connect computers and devices using protocols like TCP/IP. Types of networks include LANs, WANs, and intranets. Routers, bridges, and gateways connect different networks.

Network Security Tools. Firewalls protect networks from unauthorized access. Intrusion Detection Systems (IDS) detect attacks. Snort is an open-source NIDS.

Network Attacks. Common network attacks include Distributed Denial of Service (DDoS), identity spoofing, man-in-the-middle attacks, and social engineering. Incident response plans help organizations respond to breaches.

10. Mobile Device Forensics: Pocketfuls of Evidence

Small-scale mobile devices such as cell phones and GPS units are everywhere.

Cellular Networks. Cellular networks comprise cells, base stations, and mobile switching centers (MSC). Cellular networks use transmission schemes such as CDMA, GSM, and iDEN.

Mobile Device Evidence. Mobile devices store call history, text messages, email, pictures, videos, contacts, location information, and more. SIM cards store subscriber information.

Acquisition and Tools. Cell phone data can be acquired physically (bit-for-bit copy) or logically (files and folders). Cell phone forensic tools include Cellebrite UFED, AccessData MPE+, and Paraben Device Seizure.

11. Future Challenges: Cloud, SSDs, and Standards

There are two “game-changing” technologies that are upon us that will have a huge impact on not only the technical aspect of digital forensics but the legal piece as well.

Cloud Forensics. Cloud computing presents technical and legal challenges. Data are stored in complex virtual environments that can be located anywhere in the world. Forensic tools for cloud environments are lacking.

Solid State Drives (SSDs). SSDs make data recovery difficult due to their architecture and data management techniques. Traditional data recovery methods are often ineffective.

Standards and Controls. The digital forensics community needs to develop standards and controls to ensure the integrity and reliability of its work. This includes addressing legal and ethical issues.

Last updated: February 17, 2025