Guide to Computer Forensics and Investigations Fourth Edition
Chapter 4 Data Acquisition
Modified 9-23-10
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
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
Understanding Storage Formats for Digital Evidence
Understanding Storage Formats for Digital Evidence
Two types of data acquisition
Static acquisition
Copying a hard drive from a powered-off system Used to be the standard Does not alter the data, so it's repeatable
Live acquisition
Copying data from a running computer Now the preferred type, because of hard disk encryption Cannot be repeated exactlyalters the data Also, collecting RAM data is becoming more important But RAM data has no timestamp, which makes it much harder to use
Understanding Storage Formats for Digital Evidence
Terms used for a file containing evidence data
Bit-stream copy Bit-stream image Image Mirror Sector copy
They all mean the same thing
Understanding Storage Formats for Digital Evidence
Three formats
Raw format Proprietary formats Advanced Forensics Format (AFF)
Raw Format
This is what the Linux dd command makes Bit-by-bit copy of the drive to a file Advantages
Fast data transfers Can ignore minor data read errors on source drive Most computer forensics tools can read raw format
Raw Format
Disadvantages
Requires as much storage as original disk or data Tools might not collect marginal (bad) sectors
Low threshold of retry reads on weak media spots Commercial tools use more retries than free tools
Validation check must be stored in a separate file
Message Digest 5 ( MD5) Secure Hash Algorithm ( SHA-1 or newer) Cyclic Redundancy Check ( CRC-32)
Proprietary Formats
Features offered
Option to compress or not compress image files Can split an image into smaller segmented files
Such as to CDs or DVDs With data integrity checks in each segment
Can integrate metadata into the image file
Hash data Date & time of acquisition Investigator name, case name, comments, etc.
Proprietary Formats
Disadvantages
Inability to share an image between different tools File size limitation for each segmented volume
Typical segmented file size is 650 MB or 2 GB
Expert Witness format is the unofficial standard
Used by EnCase, FTK, X-Ways Forensics, and SMART Can produce compressed or uncompressed files File extensions .E01, .E02, .E03,
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
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
Determining the Best Acquisition Method
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 Sparse
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 Tools: ProDiscover, EnCase, FTK, SMART, Sleuth Kit, X-Ways, iLook
Bit-stream disk-to-disk
Used when disk-to-image copy is not possible
Because of hardware or software errors or incompatibilities This problem is more common when acquiring older drives
Adjusts target disks geometry (cylinder, head, and track configuration) to match the suspect's drive Tools: EnCase, SafeBack (MS-DOS), Snap Copy
Logical Acquisition and Sparse Acquisition
When your time is limited, and evidence disk is large Logical acquisition captures only specific files of interest to the case
Such as Outlook .pst or .ost files
Sparse acquisition collects only some of the data
I am finding contradictory claims about thiswait until we have a real example for clarity
Compressing Disk Images
Lossless compression might compress a disk image by 50% or more But files that are already compressed, like ZIP files, wont compress much more
Error in textbook: JPEGs use lossy compression and degrade image quality (p. 104)
Use MD5 or SHA-1 hash to verify the image
Tape Backup
When working with large drives, an alternative is using tape backup systems No limit to size of data acquisition
Just use many tapes
But its slow
Returning Evidence Drives
In civil litigation, a discovery order may require you to return the original disk after imaging it If you cannot retain the disk, make sure you make the correct type of copy (logical or bitstream)
Ask your client attorney or your supervisor what is requiredyou usually only have one chance
Contingency Planning for Image Acquisitions
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 (link Ch 4c)
Be prepared to deal with encrypted drives
Whole disk encryption feature in Windows Vista Ultimate and Enterprise editions
Encrypted Hard Drives
Windows BitLocker TrueCrypt If the machine is on, a live acquisition will capture the decrypted hard drive Otherwise, you will need the key or passphrase
The suspect may provide it There are some exotic attacks
Cold Boot (link Ch 4e) Passware (Ch 4f) Electron microscope (Ch 4g)
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 cant acquire data from a disks host protected area
Windows 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 Works in Windows XP SP2, Vista, and Win 7
Acquiring Data with a Linux Boot CD
Linux can read hard drives that are mounted as read-only Windows OSs and newer Linux automatically mount and access a drive Windows will write to the Recycle Bin, and sometimes to the NTFS Journal, just from booting up with a hard drive connected Linux kernel 2.6 and later write metadata to the drive, such as mount point configurations for an ext2 or ext3 drive All these changes corrupt the evidence
Acquiring Data with a Linux Boot CD
Forensic Linux Live CDs mount all drives read-only
Which eliminates the need for a write-blocker
Using Linux Live CD Distributions
Forensic Linux Live CDs
Contain additional utilities
Forensic Linux Live CDs
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 (French interface)
Preparing a target drive for acquisition in Linux
Modern linux distributions can use Microsoft FAT and NTFS partitions
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
Acquiring data with dd in Linux
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
dd command is intended as a data management tool
Not designed for forensics acquisitions
Acquiring data with dcfldd in Linux
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
Capturing an Image with ProDiscover Basic
Connecting the suspects drive to your workstation
Document the chain of evidence for the drive Remove the drive from the suspects computer Configure the suspect drives jumpers as needed Connect the suspect drive to a write-blocker device Create a storage folder on the target drive
Using ProDiscovers 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)
Capturing an Image with ProDiscover Basic (continued)
Capturing an Image with ProDiscover Basic (continued)
Using ProDiscovers 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
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 cant acquire drives host protected area (but ProDiscover can)
Capturing an Image with AccessData FTK Imager (continued)
Capturing an Image with AccessData FTK Imager (continued)
Steps
Boot to Windows Connect evidence disk to a write-blocker Connect target disk Start FTK Imager Create Disk Image
Use Physical Drive option
Capturing an Image with AccessData FTK Imager (continued)
Capturing an Image with AccessData FTK Imager (continued)
Capturing an Image with AccessData FTK Imager (continued)
Capturing an Image with AccessData FTK Imager (continued)
Validating Data Acquisitions
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
MD5 has collisions, so it is not perfect, but its still widely used SHA-1 has some collisions but its better than MD5 A new hashing function will soon be chosen by NIST
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
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 dont contain metadata
Separate manual validation is recommended for all raw acquisitions
Performing RAID Data Acquisitions
Performing RAID Data Acquisitions
Size is the biggest concern
Many RAID systems now have terabytes of data
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 (Striped)
Provides rapid access and increased storage Lack of redundancy
RAID 1 (Mirrored)
Designed for data recovery More expensive than RAID 0
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 striping and dedicated parity
RAID 4
Data is written in blocks
Understanding RAID (continued)
Understanding RAID (continued)
Understanding RAID (continued)
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
Understanding RAID (continued)
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 youre making an image
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
Using Remote Network Acquisition Tools
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
LANs 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 Remote access tool could be blocked by antivirus
Remote Acquisition with ProDiscover Investigator
Preview a suspects drive remotely while its in use Perform a live acquisition
Also called a smear because data is being altered
Encrypt the connection Copy the suspect computers RAM Use the optional stealth mode to hide the connection
Remote Acquisition with ProDiscover Incident Response
All the functions of ProDiscover Investigator plus
Capture volatile system state information Analyze current running processes Locate unseen files and processes Remotely view and listen to IP ports Run hash comparisons to find Trojans and rootkits Create a hash inventory of all files remotely
PDServer Remote Agent
ProDiscover utility for remote access Needs to be loaded on the suspect computer 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
Remote Connection Security Features
Password Protection Encrypted communications Secure Communication Protocol Write Protected Trusted Binaries Digital Signatures
Remote Acquisition with EnCase Enterprise
Remotely acquires 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
Other Remote Acquisition Tools
R-Tools R-Studio WetStone LiveWire F-Response
Remote Acquisition with Runtime Software
Compact Shareware Utilities
DiskExplorer for FAT DiskExplorer for NTFS HDHOST (Remote access program)
Features for acquisition
Create a raw format image file Segment the raw format or compressed image Access network computers drives
Using Other ForensicsAcquisition Tools
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
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
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
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
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
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
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
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
