Forensic analysis of hard drives is a crucial skill for cybersecurity professionals. When a computer is involved in illegal activity, has been infected with malware, or contains evidence pertinent to an investigation, forensic examiners need to know how to properly extract that information. Performing a forensic hard drive inspection requires specialized tools, strict protocols, and meticulous documentation. The data uncovered can then be analyzed to determine what happened on the system.
Why Conduct a Forensic Hard Drive Inspection?
There are several key reasons to forensically inspect a hard drive:
- Recover deleted files – When a file is deleted, the data itself is not actually erased from the hard drive. Forensic tools can scan the drive and recover these deleted files.
- Find evidence of illegal activity – If a computer is suspected of being used for financial fraud, distributing illicit materials, or other crimes, the hard drive can be inspected to find supporting evidence.
- Determine the cause of a cybersecurity incident – When an organization suffers a malware infection, data breach, or other cyberattack, forensic analysis can identify ground zero and how the attackers gained entry.
- Audit computer usage – Forensic techniques can reveal unauthorized activities by employees, such as improper Internet usage or accessing inappropriate content.
- Support insurance claims and lawsuits – The results of a forensic investigation can become critical evidence in court cases and insurance claims resulting from cyber incidents.
By forensically examining hard drives in these situations, cybersecurity professionals can uncover valuable digital evidence and insights. This information is often pivotal in determining what really happened in an incident.
How Does Forensic Hard Drive Analysis Work?
Forensic hard drive inspection utilizes a number of techniques to find and interpret digital evidence. Here are some of the primary steps involved:
- Imaging the hard drive – The first and most important step is to create a complete forensic image (or clone) of the hard drive. This binary image file preserves the drive contents without alteration for subsequent inspection.
- Authenticating the image – Forensic examiners use mathematical hashing functions to validate the forensic image. This proves the image perfectly matches the original and has not been altered.
- Analyzing the file systems – The cloned drive is then attached to a forensic workstation for analysis. Examiners inspect critical file system data structures, directory entries, and metadata for clues.
- Recovering deleted files and partitions – Forensic tools piece together remnants of deleted files and partitions that may hold evidence. This provides access to data the user wanted to hide.
- Cracking encrypted volumes – Some users encrypt partitions or entire drives. Forensic specialists use password crackers and other methods to bypass or decrypt these volumes.
- Extracting Internet history and traces – Web browsers, email clients, chat logs, and network services leave extensive information about online activities that can be recovered forensically.
- Identifying external storage – Evidence of external media like USB drives and optical discs may be uncovered through analysis of Internet history, logs, registry data, and file timestamps.
- Data carving – When high-level file system data is missing, forensic tools carve raw data looking for specific file headers and footers. For example, JPEGs start with 0xFFD8 and end with 0xFFD9.
By utilizing these and other advanced forensic techniques, trained examiners can uncover a wealth of details from a suspect hard drive. The findings help reconstruct user activities, relationships, motives, and timelines.
Forensic Hard Drive Inspection Process
Proper handling and documentation is critical throughout the forensic hard drive inspection process. Following consistent procedures preserves the evidentiary value of any data recovered. Key steps include:
- Securing the evidence – Unplug the suspect computer without shutting it down. Document the hardware configuration. Photograph connections. Place evidence tape over connectors and chassis openings. The goal is to prevent data alteration.
- Establishing chain of custody – Every person taking custody of evidence must be documented. Meticulous records prove who had access and that data could not have been modified without detection.
- Validating and imaging drives – After connecting drives to the forensic workstation, their model and serial numbers are validated against chain of custody records. A cryptographic hash is generated prior to imaging to later authenticate the forensic copy.
- Analyzing data – With the forensic image authenticated, the drive contents are indexed and searched using forensic software tools. The examiner looks for files and artifacts relevant to the particular investigation.
- Documenting the findings – All activities taken during the analysis phase are recorded in notes, case logs, and through screen captures. Careful documentation helps demonstrate adherence to forensic procedures.
- Generating a report – The forensic examiner produces a detailed report summarizing the methodology, significant data findings, and their interpretation based on training and experience.
Strict adherence to these best practices helps ensure the admissibility and integrity of digital evidence extracted through forensic hard drive analysis.
Forensic Hard Drive Tools
Specialized forensic software tools automate many aspects of the hard drive inspection process. Both open source and commercial products are widely used:
Drive Imaging
– FTK Imager
– Guymager
– DCFLdd
– Drive Cloner Rx
These tools create forensic-quality duplicate images quickly and reliably. Some also compute hashes to authenticate the integrity of the copies.
Analysis Tools
– Autopsy
– SANS Investigative Forensic Toolkit (SIFT)
– ProDiscover
– EnCase Forensic
Multi-function suites that index drive contents, carve deleted files, crack passwords, reconstruct web activity, and visualize timelines.
File Recovery
– Recuva
– PhotoRec
– Foremost
– Lazesoft Recovery Suite
Used to reliably recover deleted files and partitions marked as empty space. Often can resurrect data lost due to reformatting or OS reinstallation.
Password Cracking
– Ophcrack
– Cain and Abel
– John the Ripper
– Elcomsoft Forensic Disk Decryptor
These tools crack weak passwords protecting encrypted volumes, compressed archives, and password-locked documents. Employ wordlists, brute force, and decryption.
Internet Artifact Parsing
– NetAnalysis
– X-Ways Internet History Browser
– Magnet Forensics IEF
Reconstructs web browsing sessions, extracts chats, identifies cloud storage access, and carves out other traces of online activity.
Hex Editors
– HxD
– WinHex
– Hex Fiend
Low-level tools that display hard drive contents in hexadecimal format. Allows granular analysis of raw data structures and headers/footers.
Write Blocking
– Tableau Forensic SATA/IDE Bridge
– WiebeTech Forensic UltraDock v5
Hardware devices that prevent modification of drives during imaging and analysis. Critical for maintaining forensic data integrity.
Combining multiple tools is necessary in most cases to thoroughly reconstruct user activities, uncover all relevant artifacts, and capture necessary evidence from a hard drive.
Key Forensic Hard Drive Analysis Techniques
Some of the most important techniques used by forensic hard drive examiners include:
Review File System Metadata
File creation, access, and modification timestamps can reveal details about user behavior and data relevance. Analyzing filesystem structures shows which directories and files were accessed most recently.
Check System Logs
Logs generated by the operating system and applications track events, errors, network connections, and administrator activities. These can point to suspicious behaviors.
Recover Deleted Files and Folders
While the filesystem marks disk space from deleted items as empty, the actual data remains until being overwritten by new files. Forensics can resurrect deleted content.
Inspect Swap and Unallocated Space
Valuable data ends up in swap space during computer usage. Unallocated clusters also contain file fragments left by the OS. Forensic tools can extract hidden nuggets from these areas.
Lookup File Signatures
Unique header patterns identify many file types. Forensic utilities scan drives looking for these signatures to recover files marked as empty space. Media files are common targets.
Identify External Storage
Evidence of external devices like USB drives and flash cards may be found through analysis of logs, update cycles, web history, and registry data. This shows attempts to exfiltrate data off the computer.
Parse Internet History and Artifacts
Browser histories, cached web pages, cookies, downloads, and other traces paint a detailed picture of the user’s online activities and can point to sources of malware infections.
Inspect Emails and Chat Logs
Emails and chat messages may contain critical evidence. Forensics tools extract these communications from client software, web mail, backup files, and unallocated disk space.
Report Writing for Forensic Hard Drive Examination
The report generated by the forensic examiner documents all findings and activities relevant to the analysis. These reports have a typical structure:
Background and Objectives
This section states the background of the case and goals of the hard drive analysis based on the original request. This sets the stage for the report.
Methodology
Documents every step taken during the forensic process, including imaging, authentication, tools, techniques, analyses performed, and software settings.
Findings
Details the significant digital evidence discovered during forensic procedures. Uses direct quotes, screenshots, table summaries, and visual timelines.
Interpretations
The examiner interprets the implications of the findings based on their expertise. For example, this could identify the source of a malware infection uncovered on the system.
Supporting Materials
Supplementary exhibits like disk images, log files, screenshots, and tool reports. This provides proof to support conclusions.
Effective report writing is crucial, as the report will serve as the record and evidence of the entire forensic hard drive inspection process. Reports must be clear, accurate, and meticulously detailed.
Challenges of Forensic Hard Drive Analysis
While an extremely valuable investigative technique, forensic hard drive analysis also comes with some notable challenges:
- Encrypted volumes can be impossible to decrypt without passwords or keys. Users increasingly leverage disk encryption to thwart inspection.
- Solid state drives lack recoverable remnant data due to wear leveling and TRIM commands. Deleted files quickly become unrecoverable on SSDs.
- Antiforensic techniques like data wiping, metadata scrubbing, and disk formatting can cover the tracks of illegal activities.
- As hard drives grow larger in capacity, imaging times increase. Performing complete forensic copies takes longer.
- Determining data relevance and recognizing meaningful evidence becomes more difficult as drives fill with more user content.
- Adhering to strict forensic processes is labor-intensive and time-consuming compared to casual disk inspection methods.
Examiners must constantly adapt to new technology trends that introduce barriers to forensic disk analysis. But as cyberattacks and cybercrime accelerate, the ability to extract digital evidence from hard drives remains critical.
Conclusion
Forensic analysis of hard drives enables the recovery, interpretation, and preservation of data that can serve as key evidence in legal proceedings and investigations. By following best practices for drive imaging, leveraging forensic software tools, and meticulously documenting the examination process, digital evidence can be reliably acquired from storage media. While increasing disk sizes, encryption, and antiforensic techniques present challenges, forensic hard drive inspection remains an indispensable digital forensic skill for recovering probative information.