Solid State Drive (SSD) Forensics

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Solid State Drives pose a variety of interesting challenges for computer forensics in comparison with traditional rotating magnetic platter hard drives.

Most SSD devices are based on flash memory; some have battery backed SRAM or DRAM with a flash backing store.

Flash has a number of key properties that complicate its use in computer storage systems and subsequent forensic analysis:

  1. Internally, flash memory is not divided into the traditional 512 byte blocks, but instead is in pages of 2KiB, 4KiB, or larger, although it is still presented to the host computer in blocks
  2. Whilst hard drives can be written in a single pass, flash memory pages must be erased (in whole) before they can be rewritten.
  3. Rewriting a block at the operating system level does not necessarily rewrite the same page in the flash memory due to the controller remapping data to spread wear or avoid failing pages
  4. Each page can be erased and rewritten a limited number of times – typically 1000 to 10,000. (Hard drive sectors, in contrast, can be rewritten millions of times or more.)
  5. Flash data is often encrypted on the drive, and can be "erased" by telling the controller to forget the old key and generate a new one, as well as marking all blocks as unused

The controller in a flash SSD is significantly more complex in the number of tasks it has to perform in comparison to a magnetic rotating drive, with the following features:

  1. wear leveling – that is, spreading the writes to flash out among different sectors. Wear leveling is typically done with a flash translation layer that maps logical sectors (or LBAs) to physical pages. Most FTLs are contained within the SSD device and are not accessible to end users.


Bibliography

Michael Wei, Laura M. Grupp, Frederick M. Spada, Steven Swanson - Reliably Erasing Data from Flash-Based Solid State Drives
FAST 2011 ,2011
http://cseweb.ucsd.edu/users/m3wei/assets/pdf/FMS-2010-Secure-Erase.pdf
Bibtex
Author : Michael Wei, Laura M. Grupp, Frederick M. Spada, Steven Swanson
Title : Reliably Erasing Data from Flash-Based Solid State Drives
In : FAST 2011 -
Address :
Date : 2011

Graeme B. Bell, Richard Boddington - Solid State Drives: The Beginning of the End for Current Practice in Digital Forensic Recovery?
Journal of Digital Forensics, Security and Law 5,2011
http://www.jdfsl.org/subscriptions/JDFSL-V5N3-Bell.pdf
Bibtex
Author : Graeme B. Bell, Richard Boddington
Title : Solid State Drives: The Beginning of the End for Current Practice in Digital Forensic Recovery?
In : Journal of Digital Forensics, Security and Law -
Address :
Date : 2011

Billard, David, Hauri, Rolf - Making sense of unstructured flash-memory dumps
Proceedings of the 2010 ACM Symposium on Applied Computing pp. 1579--1583, New York, NY, USA,2010
http://doi.acm.org/10.1145/1774088.1774426
Bibtex
Author : Billard, David, Hauri, Rolf
Title : Making sense of unstructured flash-memory dumps
In : Proceedings of the 2010 ACM Symposium on Applied Computing -
Address : New York, NY, USA
Date : 2010

James E. Regan - The Forensic Potential of Flash Memory
Master's Thesis, Naval Postgraduate School , Monterey, CA,2009
http://handle.dtic.mil/100.2/ADA509258
Bibtex
Author : James E. Regan
Title : The Forensic Potential of Flash Memory
In : Master's Thesis, Naval Postgraduate School -
Address : Monterey, CA
Date : 2009

Phillips, B. J., Schmidt, C. D., Kelly, D. R. - Recovering data from USB flash memory sticks that have been damaged or electronically erased
Proceedings of the 1st international conference on Forensic applications and techniques in telecommunications, information, and multimedia and workshop pp. 19:1--19:6, ICST, Brussels, Belgium, Belgium,2008
http://portal.acm.org/citation.cfm?id=1363217.1363243
Bibtex
Author : Phillips, B. J., Schmidt, C. D., Kelly, D. R.
Title : Recovering data from USB flash memory sticks that have been damaged or electronically erased
In : Proceedings of the 1st international conference on Forensic applications and techniques in telecommunications, information, and multimedia and workshop -
Address : ICST, Brussels, Belgium, Belgium
Date : 2008

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