Unit 1.ppt
Document Details
Full Transcript
Storage Formats for Digital Evidence Understanding Storage Formats 2 for Digital Evidence Two types of data acquisition Static acquisition Copying a hard drive from a powered-off system Used to b...
Storage Formats for Digital Evidence Understanding Storage Formats 2 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 exactly—alters 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 3 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 4 for Digital Evidence Three formats Raw format Proprietary formats Advanced Forensics Format (AFF) Raw Format 5 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 6 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 7 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 8 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 Usedby EnCase, FTK, X-Ways Forensics, and SMART Can produce compressed or uncompressed files File extensions.E01,.E02,.E03, … Advanced Forensics Format 9 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 10 (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 12 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 13 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 14 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 disk’s geometry (cylinder, head, and track configuration) to match the suspect's drive Tools: EnCase, SafeBack (MS-DOS), Snap Copy Logical Acquisition and Sparse 15 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 this—wait until we have a real example for clarity Compressing Disk Images 16 Lossless compression might compress a disk image by 50% or more Butfiles that are already compressed, like ZIP files, won’t 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 Returning Evidence Drives 17 Incivil litigation, a discovery order may require you to return the original disk after imaging it Ifyou 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 required—you usually only have one chance Contingency Planning for Image Acquisitions Contingency Planning for Image 19 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 20 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 21 Acquisition tools for Windows Advantages Makeacquiring evidence from a suspect drive more convenient Especially when used with hot-swappable devices Disadvantages Mustprotect acquired data with a well-tested write- blocking hardware device Tools can’t acquire data from a disk’s host protected area Windows Write-Protection with 22 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 Validating Data Acquisitions Validating Data Acquisitions 24 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 it’s still widely used SHA-1 has some collisions but it’s better than MD5 A new hashing function will soon be chosen by NIST Linux Validation Methods 25 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 26 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 Performing RAID Data Acquisitions Performing RAID Data 28 Acquisitions Size is the biggest concern Many RAID systems now have terabytes of data Understanding RAID 29 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) 30 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) 31 Understanding RAID (continued) 32 Acquiring RAID Disks 33 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 Acquiring RAID Disks (continued) 34 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 36 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 Remote access tool could be blocked by antivirus Remote Acquisition with 37 ProDiscover Investigator Preview a suspect’s drive remotely while it’s in use Perform a live acquisition Also called a “smear” because data is being altered Encrypt the connection Copy the suspect computer’s RAM Use the optional stealth mode to hide the connection Remote Acquisition with 38 ProDiscover Incident Response Allthe 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 39 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 40 Features Password Protection Encrypted communications Secure Communication Protocol Write Protected Trusted Binaries Digital Signatures Remote Acquisition with EnCase 41 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 42 R-Tools R-Studio WetStone LiveWire F-Response Remote Acquisition with Runtime 43 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 Forensics- Acquisition Tools Using Other Forensics-Acquisition 45 Tools Tools SnapBack DatArrest SafeBack DIBS USA RAID ILook Investigator IXimager Vogon International SDi32 ASRData SMART Australian Department of Defence PyFlag SnapBack DatArrest 46 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 47 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) 48 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 49 Rapid Action Imaging Device (RAID) Makes forensically sound disk copies Portablecomputer system designed to make disk-to-disk images Copieddisk can then be attached to a write- blocker device ILook Investigator IXimager 50 Iximager Runs from a bootable floppy or CD Designed to work only with ILook Investigator Can acquire single drives and RAID drives ASRData SMART 51 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 52 PyFlag PyFlag tool Intended as a network forensics analysis tool Cancreate proprietary format Expert Witness image files Uses sgzip and gzip in Linux Challenges of Computer Forensics 53 A microcomputer may have 60-GB or more storage capacity. There are more than 2.2 billion messages expected to be sent and received (in US) per day. There are more than 3 billion indexed Web pages world wide. There are more than 550 billion documents on line. Exabytes of data are stored on tape or hard drives. (Source: Marcella, Albert, et al, Cyber Forensic, 2002.) Challenges of Computer Forensics 54 (continued) How to collect the specific, probative, and case- related information from very large groups of files? Link analysis Visualization Enabling techniques for lead discovery from very large groups of files: Text mining Data mining Intelligent information retrieval
