Guide to Computer Forensics and Investigations Fourth Edition
Chapter 4 Data Acquisition

Objectives
• List digital evidence storage formats • Explain ways to determine the best acquisition method • Describe contingency planning for data acquisitions • Explain how to use acquisition tools

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Objectives (continued)
• Explain how to validate data acquisitions • Describe RAID acquisition methods • Explain how to use remote network acquisition tools • List other forensic tools available for data acquisitions

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Understanding Storage Formats for Digital Evidence
• Three formats
– Raw format – Proprietary formats – Advanced Forensics Format (AFF)

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Raw Format
• Makes it possible to write bit-stream data to files • Advantages
– Fast data transfers – Can ignore minor data read errors on source drive – Most computer forensics tools can read raw format

• Disadvantages
– Requires as much storage as original disk or data – Tools might not collect marginal (bad) sectors

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Proprietary Formats
• Features offered
– Option to compress or not compress image files – Can split an image into smaller segmented files – Can integrate metadata into the image file

• Disadvantages
– Inability to share an image between different tools – File size limitation for each segmented volume

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Advanced Forensics Format
• Developed by Dr. Simson L. Garfinkel of Basis Technology Corporation • Design goals
– Provide compressed or uncompressed image files – No size restriction for disk-to-image files – Provide space in the image file or segmented files for metadata – Simple design with extensibility – Open source for multiple platforms and OSs

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Advanced Forensics Format (continued)
• Design goals (continued)
– Internal consistency checks for self-authentication

• File extensions include .afd for segmented image files and .afm for AFF metadata • AFF is open source

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Determining the Best Acquisition Method
• Types of acquisitions
– Static acquisitions and live acquisitions

• Four methods
– – – – Bit-stream disk-to-image file Bit-stream disk-to-disk Logical disk-to-disk or disk-to-disk data Sparse data copy of a file or folder

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Determining the Best Acquisition Method (continued)
• Bit-stream disk-to-image file
– – – – Most common method Can make more than one copy Copies are bit-for-bit replications of the original drive ProDiscover, EnCase, FTK, SMART, Sleuth Kit, XWays, iLook

• Bit-stream disk-to-disk
– When disk-to-image copy is not possible – Consider disk’s geometry configuration – EnCase, SafeBack, SnapCopy
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Determining the Best Acquisition Method (continued)
• Logical acquisition or sparse acquisition
– When your time is limited – Logical acquisition captures only specific files of interest to the case – Sparse acquisition also collects fragments of unallocated (deleted) data – For large disks – PST or OST mail files, RAID servers

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Determining the Best Acquisition Method (continued)
• When making a copy, consider:
– Size of the source disk
• Lossless compression might be useful • Use digital signatures for verification

– When working with large drives, an alternative is using tape backup systems – Whether you can retain the disk

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Contingency Planning for Image Acquisitions
• Create a duplicate copy of your evidence image file • Make at least two images of digital evidence
– Use different tools or techniques

• Copy host protected area of a disk drive as well
– Consider using a hardware acquisition tool that can access the drive at the BIOS level

• Be prepared to deal with encrypted drives
– Whole disk encryption feature in Windows Vista Ultimate and Enterprise editions
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Using Acquisition Tools
• Acquisition tools for Windows
– Advantages
• Make acquiring evidence from a suspect drive more convenient – Especially when used with hot-swappable devices

– Disadvantages
• Must protect acquired data with a well-tested writeblocking hardware device • Tools can’t acquire data from a disk’s host protected area

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Windows XP Write-Protection with USB Devices
• USB write-protection feature
– Blocks any writing to USB devices

• Target drive needs to be connected to an internal PATA (IDE), SATA, or SCSI controller • Steps to update the Registry for Windows XP SP2
– Back up the Registry – Modify the Registry with the write-protection feature – Create two desktop icons to automate switching between enabling and disabling writes to USB device
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Windows XP Write-Protection with USB Devices (continued)

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Acquiring Data with a Linux Boot CD
• Linux can access a drive that isn’t mounted • Windows OSs and newer Linux automatically mount and access a drive • Forensic Linux Live CDs don’t access media automatically
– Which eliminates the need for a write-blocker

• Using Linux Live CD Distributions
– Forensic Linux Live CDs
• Contain additionally utilities
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Acquiring Data with a Linux Boot CD (continued)
• Using Linux Live CD Distributions (continued)
– Forensic Linux Live CDs (continued)
• Configured not to mount, or to mount as read-only, any connected storage media • Well-designed Linux Live CDs for computer forensics – Helix – Penguin Sleuth – FCCU

• Preparing a target drive for acquisition in Linux
– Linux distributions can create Microsoft FAT and NTFS partition tables
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Acquiring Data with a Linux Boot CD (continued)
• Preparing a target drive for acquisition in Linux (continued)
– fdisk command lists, creates, deletes, and verifies partitions in Linux – mkfs.msdos command formats a FAT file system from Linux

• Acquiring data with dd in Linux
– dd (“data dump”) command
• Can read and write from media device and data file • Creates raw format file that most computer forensics analysis tools can read
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Acquiring Data with a Linux Boot CD (continued)
• Acquiring data with dd in Linux (continued)
– Shortcomings of dd command
• Requires more advanced skills than average user • Does not compress data

– dd command combined with the split command
• Segments output into separate volumes

• Acquiring data with dcfldd in Linux
– dd command is intended as a data management tool
• Not designed for forensics acquisitions
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Acquiring Data with a Linux Boot CD (continued)
• Acquiring data with dcfldd in Linux (continued)
– dcfldd additional functions
• • • • Specify hex patterns or text for clearing disk space Log errors to an output file for analysis and review Use several hashing options Refer to a status display indicating the progress of the acquisition in bytes • Split data acquisitions into segmented volumes with numeric extensions • Verify acquired data with original disk or media data

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Capturing an Image with ProDiscover Basic
• Connecting the suspect’s drive to your workstation
– – – – – Document the chain of evidence for the drive Remove the drive from the suspect’s computer Configure the suspect drive’s jumpers as needed Connect the suspect drive Create a storage folder on the target drive

• Using ProDiscover’s Proprietary Acquisition Format
– Image file will be split into segments of 650MB – Creates image files with an .eve extension, a log file (.log extension), and a special inventory file (.pds extension)
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Capturing an Image with ProDiscover Basic (continued)

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Capturing an Image with ProDiscover Basic (continued)
• Using ProDiscover’s Raw Acquisition Format
– Select the UNIX style dd format in the Image Format list box – Raw acquisition saves only the image data and hash value

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Capturing an Image with AccessData FTK Imager
• Included on AccessData Forensic Toolkit • View evidence disks and disk-to-image files • Makes disk-to-image copies of evidence drives
– At logical partition and physical drive level – Can segment the image file

• Evidence drive must have a hardware writeblocking device
– Or the USB write-protection Registry feature enabled

• FTK Imager can’t acquire drive’s host protected area
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Capturing an Image with AccessData FTK Imager (continued)

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Capturing an Image with AccessData FTK Imager (continued)
• Steps
– – – – – Boot to Windows Connect evidence disk to a write-blocker Connect target disk to write-blocker Start FTK Imager Create Disk Image
• Use Physical Drive option

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Capturing an Image with AccessData FTK Imager (continued)

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Capturing an Image with AccessData FTK Imager (continued)

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Capturing an Image with AccessData FTK Imager (continued)

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Capturing an Image with AccessData FTK Imager (continued)

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Validating Data Acquisitions
• Most critical aspect of computer forensics • Requires using a hashing algorithm utility • Validation techniques
– CRC-32, MD5, and SHA-1 to SHA-512

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Linux Validation Methods
• Validating dd acquired data
– You can use md5sum or sha1sum utilities – md5sum or sha1sum utilities should be run on all suspect disks and volumes or segmented volumes

• Validating dcfldd acquired data
– Use the hash option to designate a hashing algorithm of md5, sha1, sha256, sha384, or sha512 – hashlog option outputs hash results to a text file that can be stored with the image files – vf (verify file) option compares the image file to the original medium
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Windows Validation Methods
• Windows has no built-in hashing algorithm tools for computer forensics
– Third-party utilities can be used

• Commercial computer forensics programs also have built-in validation features
– Each program has its own validation technique

• Raw format image files don’t contain metadata
– Separate manual validation is recommended for all raw acquisitions
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Performing RAID Data Acquisitions
• Size is the biggest concern
– Many RAID systems now have terabytes of data

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Understanding RAID
• Redundant array of independent (formerly “inexpensive”) disks (RAID)
– Computer configuration involving two or more disks – Originally developed as a data-redundancy measure

• RAID 0
– Provides rapid access and increased storage – Lack of redundancy

• RAID 1
– Designed for data recovery – More expensive than RAID 0
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Understanding RAID (continued)
• RAID 2
– – – – Similar to RAID 1 Data is written to a disk on a bit level Has better data integrity checking than RAID 0 Slower than RAID 0

• RAID 3
– Uses data stripping and dedicated parity

• RAID 4
– Data is written in blocks
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Understanding RAID (continued)

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Understanding RAID (continued)

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Understanding RAID (continued)

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Understanding RAID (continued)
• RAID 5
– Similar to RAIDs 0 and 3 – Places parity recovery data on each disk

• RAID 6
– Redundant parity on each disk

• RAID 10, or mirrored striping
– Also known as RAID 1+0 – Combination of RAID 1 and RAID 0

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Understanding RAID (continued)

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Acquiring RAID Disks
• Concerns
– – – – – How much data storage is needed? What type of RAID is used? Do you have the right acquisition tool? Can the tool read a forensically copied RAID image? Can the tool read split data saves of each RAID disk?

• Older hardware-firmware RAID systems can be a challenge when you’re making an image
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Acquiring RAID Disks (continued)
• Vendors offering RAID acquisition functions
– – – – – Technologies Pathways ProDiscover Guidance Software EnCase X-Ways Forensics Runtime Software R-Tools Technologies

• Occasionally, a RAID system is too large for a static acquisition
– Retrieve only the data relevant to the investigation with the sparse or logical acquisition method
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Using Remote Network Acquisition Tools
• You can remotely connect to a suspect computer via a network connection and copy data from it • Remote acquisition tools vary in configurations and capabilities • Drawbacks
– LAN’s data transfer speeds and routing table conflicts could cause problems – Gaining the permissions needed to access more secure subnets – Heavy traffic could cause delays and errors
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Remote Acquisition with ProDiscover
• With ProDiscover Investigator you can:
– – – – – Preview a suspect’s drive remotely while it’s in use Perform a live acquisition Encrypt the connection Copy the suspect computer’s RAM Use the optional stealth mode

• ProDiscover Incident Response additional functions
– Capture volatile system state information – Analyze current running processes
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Remote Acquisition with ProDiscover (continued)
• ProDiscover Incident Response additional functions (continued)
– – – – Locate unseen files and processes Remotely view and listen to IP ports Run hash comparisons Create a hash inventory of all files remotely

• PDServer remote agent
– ProDiscover utility for remote access – Needs to be loaded on the suspect
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Remote Acquisition with ProDiscover (continued)
• PDServer installation modes
– Trusted CD – Preinstallation – Pushing out and running remotely

• PDServer can run in a stealth mode
– Can change process name to appear as OS function

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Remote Acquisition with ProDiscover (continued)
• Remote connection security features
– – – – – Password Protection Encryption Secure Communication Protocol Write Protected Trusted Binaries Digital Signatures

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Remote Acquisition with EnCase Enterprise
• Remote acquisition features
– Remote data acquisition of a computer’s media and RAM data – Integration with intrusion detection system (IDS) tools – Options to create an image of data from one or more systems – Preview of systems – A wide range of file system formats – RAID support for both hardware and software
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Remote Acquisition with R-Tools RStudio
• R-Tools suite of software is designed for data recovery • Remote connection uses Triple Data Encryption Standard (3DES) encryption • Creates raw format acquisitions • Supports various file systems

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Remote Acquisition with Runtime Software
• Utilities
– DiskExplorer for FAT – DiskExplorer for NTFS – HDHOST

• Features for acquisition
– Create a raw format image file – Segment the raw format or compressed image – Access network computers’ drives

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Using Other Forensics-Acquisition Tools
• Tools
– – – – – – – SnapBack DatArrest SafeBack DIBS USA RAID ILook Investigator IXimager Vogon International SDi32 ASRData SMART Australian Department of Defence PyFlag

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SnapBack DatArrest
• Columbia Data Products • Old MS-DOS tool • Can make an image on three ways
– Disk to SCSI drive – Disk to network drive – Disk to disk

• Fits on a forensic boot floppy • SnapCopy adjusts disk geometry
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NTI SafeBack
• • • • Reliable MS-DOS tool Small enough to fit on a forensic boot floppy Performs an SHA-256 calculation per sector copied Creates a log file

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NTI SafeBack (continued)
• Functions
– Disk-to-image copy (image can be on tape) – Disk-to-disk copy (adjusts target geometry)
• Parallel port laplink can be used

– Copies a partition to an image file – Compresses image files

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DIBS USA RAID
• Rapid Action Imaging Device (RAID)
– Makes forensically sound disk copies – Portable computer system designed to make disk-todisk images – Copied disk can then be attached to a write-blocker device

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ILook Investigator IXimager
• Iximager
– Runs from a bootable floppy or CD – Designed to work only with ILook Investigator – Can acquire single drives and RAID drives

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Vogon International SDi32
• Creates a raw format image of a drive • Write-blocker is needed when using this tool • Password Cracker POD
– Device that removes the password on a drive’s firmware card

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ASRData SMART
• Linux forensics analysis tool that can make image files of a suspect drive • Capabilities
– – – – Robust data reading of bad sectors on drives Mounting suspect drives in write-protected mode Mounting target drives in read/write mode Optional compression schemes

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Australian Department of Defence PyFlag
• PyFlag tool
– Intended as a network forensics analysis tool – Can create proprietary format Expert Witness image files – Uses sgzip and gzip in Linux

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Summary
• Data acquisition methods
– – – – Disk-to-image file Disk-to-disk copy Logical disk-to-disk or disk-to-data file Sparse data copy

• Several tools available
– Lossless compression is acceptable

• Plan your digital evidence contingencies • Write-blocking devices or utilities must be used with GUI acquisition tools
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Summary (continued)
• Always validate acquisition • A Linux Live CD, such as Helix, provides many useful tools for computer forensics acquisitions • Preferred Linux acquisition tool is dcfldd (not dd) • Use a physical write-blocker device for acquisitions • To acquire RAID disks, determine the type of RAID
– And then which acquisition tool to use

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