Computer Forensics Evidence Collection

Monday, August 23, 2010

Bozidar Spirovski

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Following up on A Computer Forensics Process Tutorial, here is a step-by-step tutorial on how to process a suspect computer to obtain dumps of RAM memory and Disk Drive using Helix Forensic CD.

Our suspect computer is a Windows XP Virtual Machine.

Our Example Forensic Toolkit

  • Helix forensic CD - your basic tool for the investigation
  • Evidence USB - 16 GB Capacity - for removing smaller evidence files from the evidence computer
  • Analysis computer - a windows laptop, VDK driver, for the analysis computer (if using windows) - this driver will enable you to mount a DD image created during the evidence collection
  • Sophos Antivirus and A-Squared Free Antispyware detector software for the analysis computer

I. Running state evidence collection

   1. Insert the Helix CD in the suspects computer CD/DVD drive. The Helix has an autorun so should start immediately, but be careful. If you are logged on as anything other then an administrator, you won't be able to make a dump of the full physical memory. So close the autorun, and choose the Run as option to start the Helix software, and provide the Administrator credentials.

   2. WARNING - DO NOT log off the session in order to log on as an Administrator! Ending a session will inevitably change and contaminate the content of RAM, since a lot of processes are closed upon logoff.

   3. When Helix starts, there will be a warning screen stating that Helix won't be able to protect the suspect OS environment from changing, since it's running within the suspect OS environment. But, since there is no other way to take a snapshot of the ram memory, just choose accept.

   4. You will see the startup screen of the Helix tool. The first icon is just a preview of system info, so it's not too useful. Go ahead to the second option – acquisition. It will prompt you for the source. Choose physical memory, and direct the output to the evidence USB drive.

  5. Acquisition will prompt you for the source to be dumped – choose Physical Memory
      It will ask for second confirmation and will start the dump

   6. After Memory Dump is finished, choose incident response (3rd icon on the Left menu) and click on the small arrow to go to the second screen (shown below). Run WinAudit

   7. Click on the only link and let it perform inventory of the system. Save the result as a PDF on your evidence USB

After Winaudit finishes, close it, and close the Helix mainwindow. It will ask whether you like to record all activities in a PDF file. Confirm that you wish to and save the PDF on your evidence USB.

The above process will create an MD5 hash of the memory dump on the evidence USB. Open this file and take note of the MD5 hash.

II. Disk drive evidence collection

   1. Turn off the computer ungracefully, pull the plug - this will prevent any possible shutdown scripts from running and possibly erasing data on the computer.

   2. Boot it up again, and from the BIOS select to boot from CD-ROM. In a real corporate investigation, you may need assistance of IT to provide passwords, since most corporate PC's are set-up with BIOS password and disabled from booting from CD to prevent possible information theft.

   3. Boot the Helix Linux OS

   4. When booted, select Adepto from the Forensics Menu

   5. Similarly to the memory dump above, select the drive you wish to make a dump of, and select your evidence USB as destination. For hash, you can choose severa. The example is with SHA1. After the dump is finished, choose the last tab (report) and choose to save the dump report as PDF to the evidence USB.

   6. Copy all files to your analysis computer, and verify the hashes of the memory and disk dumps again using md5sum and sha1sum, whichever you used initially.

   7. Using VDK, mount a copy of the disk image for investigation. The mount command is: vdk open path_to_dump_file\dump_filename.dd /L:free_drive_letter

HERE You can download and review the forensic log documents created in this tutorial (5.19 MB ZIP file)

Helix_Evidence_Collection_Sample_Logs.zip

Verification sums:

    * SHA1SUM c7d189a78a715fd96127677d39d5ace1d5854ea5
    * MD5SUM 9b61fad0cf4418175cb7e387c6962c49

This concludes the easy part of computer forensics - evidence collection. Shortinfosec will follow-up with exercises of the analysis part.

Cross-posted from ShortInfosec

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Benjamin Wright Bozidar: On the topic of tools . . . I'm looking for feedback. I have posted a prototype, online investigation report and evidence container. Please see description, and please critique:
http://blogs.sans.org/computer-forensics/2010/10/22/digital-forensics-investigators-write-report-store-digital-evidence/ --Ben
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