Guide to Computer Forensics and Investigations Fourth Edition
Chapter 7 Current Computer Forensics Tools

Objectives
• Explain how to evaluate needs for computer forensics tools • Describe available computer forensics software tools • List some considerations for computer forensics hardware tools • Describe methods for validating and testing computer forensics tools

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Evaluating Computer Forensics Tool Needs
• Look for versatility, flexibility, and robustness
– – – – – OS File system Script capabilities Automated features Vendor’s reputation

• Keep in mind what application files you will be analyzing

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Types of Computer Forensics Tools
• Hardware forensic tools
– Range from single-purpose components to complete computer systems and servers

• Software forensic tools
– Types
• Command-line applications • GUI applications

– Commonly used to copy data from a suspect’s disk drive to an image file
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Tasks Performed by Computer Forensics Tools
• Five major categories:
– – – – – Acquisition Validation and discrimination Extraction Reconstruction Reporting

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Tasks Performed by Computer Forensics Tools (continued)
• Acquisition
– Making a copy of the original drive

• Acquisition subfunctions:
– – – – – – – Physical data copy Logical data copy Data acquisition format Command-line acquisition GUI acquisition Remote acquisition Verification
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Tasks Performed by Computer Forensics Tools (continued)
• Acquisition (continued)
– Two types of data-copying methods are used in software acquisitions:
• Physical copying of the entire drive • Logical copying of a disk partition

– The formats for disk acquisitions vary
• From raw data to vendor-specific proprietary compressed data

– You can view the contents of a raw image file with any hexadecimal editor
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Tasks Performed by Computer Forensics Tools (continued)
• Acquisition (continued)
– Creating smaller segmented files is a typical feature in vendor acquisition tools – All computer forensics acquisition tools have a method for verification of the data-copying process
• That compares the original drive with the image

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Tasks Performed by Computer Forensics Tools (continued)
• Validation and discrimination
– Validation
• Ensuring the integrity of data being copied

– Discrimination of data
• Involves sorting and searching through all investigation data

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Tasks Performed by Computer Forensics Tools (continued)
• Validation and discrimination (continued)
– Subfunctions
• Hashing – CRC-32, MD5, Secure Hash Algorithms • Filtering – Based on hash value sets • Analyzing file headers – Discriminate files based on their types

– National Software Reference Library (NSRL) has compiled a list of known file hashes
• For a variety of OSs, applications, and images
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Tasks Performed by Computer Forensics Tools (continued)

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Tasks Performed by Computer Forensics Tools (continued)
• Validation and discrimination (continued)
– Many computer forensics programs include a list of common header values
• With this information, you can see whether a file extension is incorrect for the file type

– Most forensics tools can identify header values

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Tasks Performed by Computer Forensics Tools (continued)

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Tasks Performed by Computer Forensics Tools (continued)
• Extraction
– Recovery task in a computing investigation – Most demanding of all tasks to master – Recovering data is the first step in analyzing an investigation’s data

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Tasks Performed by Computer Forensics Tools (continued)
• Extraction (continued)
– Subfunctions
• • • • • • Data viewing Keyword searching Decompressing Carving Decrypting Bookmarking

– Keyword search speeds up analysis for investigators

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Tasks Performed by Computer Forensics Tools (continued)

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Tasks Performed by Computer Forensics Tools (continued)
• Extraction (continued)
– From an investigation perspective, encrypted files and systems are a problem – Many password recovery tools have a feature for generating potential password lists
• For a password dictionary attack

– If a password dictionary attack fails, you can run a brute-force attack

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Tasks Performed by Computer Forensics Tools (continued)
• Reconstruction
– Re-create a suspect drive to show what happened during a crime or an incident – Subfunctions
• • • • Disk-to-disk copy Image-to-disk copy Partition-to-partition copy Image-to-partition copy

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Tasks Performed by Computer Forensics Tools (continued)
• Reconstruction (continued)
– Some tools that perform an image-to-disk copy:
• • • • • SafeBack SnapBack EnCase FTK Imager ProDiscover

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Tasks Performed by Computer Forensics Tools (continued)
• Reporting
– To complete a forensics disk analysis and examination, you need to create a report – Subfunctions
• Log reports • Report generator

– Use this information when producing a final report for your investigation

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Tool Comparisons

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Other Considerations for Tools
• Considerations
– – – – Flexibility Reliability Expandability Keep a library with older version of your tools

• Create a software library containing older versions of forensics utilities, OSs, and other programs

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Computer Forensics Software Tools
• The following sections explore some options for command-line and GUI tools in both Windows and UNIX/Linux

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Command-line Forensic Tools
• The first tools that analyzed and extracted data from floppy disks and hard disks were MS-DOS tools for IBM PC file systems • Norton DiskEdit
– One of the first MS-DOS tools used for computer investigations

• Advantage
– Command-line tools require few system resources
• Designed to run in minimal configurations

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UNIX/Linux Forensic Tools
• *nix platforms have long been the primary command-line OSs • SMART
– Designed to be installed on numerous Linux versions – Can analyze a variety of file systems with SMART – Many plug-in utilities are included with SMART – Another useful option in SMART is its hex viewer

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UNIX/Linux Forensic Tools (continued)
• Helix
– One of the easiest suites to begin with – You can load it on a live Windows system
• Loads as a bootable Linux OS from a cold boot

• Autopsy and SleuthKit
– Sleuth Kit is a Linux forensics tool – Autopsy is the GUI/browser interface used to access Sleuth Kit’s tools

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UNIX/Linux Forensic Tools (continued)
• Knoppix-STD
– Knoppix Security Tools Distribution (STD)
• A collection of tools for configuring security measures, including computer and network forensics

– Knoppix-STD is forensically sound
• Doesn’t allow you to alter or damage the system you’re analyzing

– Knoppix-STD is a Linux bootable CD

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Other GUI Forensic Tools
• • • • Simplify computer forensics investigations Help training beginning investigators Most of them come into suites of tools Advantages
– Ease of use – Multitasking – No need for learning older OSs

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Other GUI Forensic Tools (continued)
• Disadvantages
– Excessive resource requirements – Produce inconsistent results – Create tool dependencies

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Computer Forensics Hardware Tools
• Technology changes rapidly • Hardware eventually fails
– Schedule equipment replacements

• When planning your budget consider:
– Failures – Consultant and vendor fees – Anticipate equipment replacement

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Forensic Workstations
• Carefully consider what you need • Categories
– Stationary – Portable – Lightweight

• Balance what you need and what your system can handle

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Forensic Workstations (continued)
• Police agency labs
– Need many options – Use several PC configurations

• Private corporation labs
– Handle only system types used in the organization

• Keep a hardware library in addition to your software library

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Forensic Workstations (continued)
• Not as difficult as it sounds • Advantages
– Customized to your needs – Save money

• Disadvantages
– Hard to find support for problems – Can become expensive if careless

• Also need to identify what you intend to analyze

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Forensic Workstations (continued)
• You can buy one from a vendor as an alternative • Examples
– F.R.E.D. – F.I.R.E. IDE

• Having vendor support can save you time and frustration when you have problems • Can mix and match components to get the capabilities you need for your forensic workstation

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Using a Write-Blocker
• Write-blocker
– Prevents data writes to a hard disk

• Software-enabled blockers
– Software write-blockers are OS dependant – Example: PDBlock from Digital Intelligence

• Hardware options
– Ideal for GUI forensic tools – Act as a bridge between the suspect drive and the forensic workstation

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Using a Write-Blocker (continued)
• Can navigate to the blocked drive with any application • Discards the written data
– For the OS the data copy is successful

• Connecting technologies
– FireWire – USB 2.0 – SCSI controllers

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Recommendations for a Forensic Workstation
• Determine where data acquisitions will take place • Data acquisition techniques
– USB 2.0 – FireWire

• Expansion devices requirements • Power supply with battery backup • Extra power and data cables

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Recommendations for a Forensic Workstation (continued)
• External FireWire and USB 2.0 ports • Assortment of drive adapter bridges • Ergonomic considerations
– Keyboard and mouse – A good video card with at least a 17-inch monitor

• High-end video card and monitor • If you have a limited budget, one option for outfitting your lab is to use high-end game PCs

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Validating and Testing Forensic Software
• Make sure the evidence you recover and analyze can be admitted in court • Test and validate your software to prevent damaging the evidence

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Using National Institute of Standards and Technology (NIST) Tools
• Computer Forensics Tool Testing (CFTT) program
– Manages research on computer forensics tools

• NIST has created criteria for testing computer forensics tools based on:
– Standard testing methods – ISO 17025 criteria for testing items that have no current standards – ISO 5725
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Using National Institute of Standards and Technology (NIST) Tools (continued)
• Your lab must meet the following criteria
– – – – – – Establish categories for computer forensics tools Identify computer forensics category requirements Develop test assertions Identify test cases Establish a test method Report test results

• Also evaluates drive-imaging tools using
– Forensic Software Testing Support Tools (FS-TST)
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Using National Institute of Standards and Technology (NIST) Tools (continued)
• National Software Reference Library (NSRL) project
– Collects all known hash values for commercial software applications and OS files
• Uses SHA-1 to generate a known set of digital signatures called the Reference Data Set (RDS)

– Helps filtering known information – Can use RDS to locate and identify known bad files

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Using Validation Protocols
• Always verify your results • Use at least two tools
– Retrieving and examination – Verification

• Understand how tools work • One way to compare results and verify a new tool is by using a disk editor
– Such as Hex Workshop or WinHex

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Using Validation Protocols (continued)
• Disk editors
– Do not have a flashy interface – Reliable tools – Can access raw data

• Computer Forensics Examination Protocol
– Perform the investigation with a GUI tool – Verify your results with a disk editor – Compare hash values obtained with both tools

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Using Validation Protocols (continued)
• Computer Forensics Tool Upgrade Protocol
– Test
• New releases • OS patches and upgrades

– If you find a problem, report it to forensics tool vendor
• Do not use the forensics tool until the problem has been fixed

– Use a test hard disk for validation purposes – Check the Web for new editions, updates, patches, and validation tests for your tools
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Summary
• Create a business plan to get the best hardware and software • Computer forensics tools functions
– – – – – Acquisition Validation and discrimination Extraction Reconstruction Reporting

• Maintain a software library on your lab

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Summary (continued)
• Computer Forensics tools types
– Software – Hardware

• Forensics software
– Command-line – GUI

• Forensics hardware
– Customized equipment – Commercial options – Include workstations and write-blockers
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Summary (continued)
• Tools that run in Windows and other GUI environments don’t require the same level of computing expertise as command-line tools • Always test your forensics tools

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