[LINK] Self-erasing flash drives destroy court evidence
Bernard Robertson-Dunn
brd at iimetro.com.au
Thu Mar 3 09:55:23 AEDT 2011
Self-erasing flash drives destroy court evidence
'Golden age' of forensics coming to close
By Dan Goodin in San Francisco
Posted in ID, 1st March 2011
The Register
http://www.theregister.co.uk/2011/03/01/self_destructing_flash_drives/
The inner workings of solid state storage devices are so fundamentally
different from traditional hard drives that forensic investigators can
no longer rely on current preservation techniques when admitting
evidence stored on them in court cases, Australian scientists said in a
research paper.
Data stored on Flash drives is often subject to a process the scientists
called “self-corrosion,” in which evidence is permanently erased or
contaminated in ways that bits stored on magnetic-based hard drives are
not. The alterations happen in the absence of any instructions from the
user. The findings introduce a “grey area” into the integrity of files
that are forensically extracted from the devices and threaten to end a
“golden age” of digital evidence gathering offered by older storage types.
“Given the pace of development in SSD memory and controller technology,
and the increasingly proliferation [sic] of manufacturers, drives, and
firmware versions, it will probably never be possible to remove or
narrow this new grey area within the forensic and legal domain,” the
scientists, from Australia's Murdoch University, wrote. “It seems
possible that the golden age for forensic recovery and analysis of
deleted data and deleted metadata may now be ending.”
For decades, investigators have worked with tape, floppy drives and hard
drives that continue to store huge amounts of information even when the
files they're contained in are marked for deletion. Even wiping the
disks isn't always enough to permanently erase the contents. SSDs, by
contrast, store data in blocks or pages of NAND-based transistor chips
that must be electronically erased before they can be reused.
As a result, most SSDs have firmware that automatically carries out
“self healing” or “garbage collection” procedures that can permanently
erase or alter files that have been marked for deletion. The process
often begins as soon as three minutes after the drive is powered on and
happens with no warning. The user need not initiate any commands, and
the drive emits no lights or makes any sounds to indicate the purging is
taking place.
What's more, the use of so-called write blockers and other techniques
designed to isolate a drive during forensic imaging offered no
protection. That's because the garbage collection is initiated by the
SSD firmware that's independent from commands issued by the computer
it's attached to.
“If garbage collection were to take place before or during forensic
extraction of the drive image, it would result in irreversible deletion
of potentially large amounts of valuable data that would ordinarily be
gathered as evidence during the forensic process – we call this
'corrosion of evidence,'” the scientists wrote.
The findings have serious consequences for criminal and civil court
cases that rely on digital evidence. If the disk from which the data
comes appears to have been tampered with after it was seized, an
opposing party frequently has grounds for having the evidence thrown out
of court. The paper comes as a growing number of computer makers
integrate SSDs into the machines they sell. The drives have many
benefits over their magnetic brethren, including speed, lower power
consumption and durability.
At first blush, the results appear to conflict with those of a recent
paper that found data fragments stored on flash drives can be virtually
indestructible.
<http://www.theregister.co.uk/2011/02/21/flash_drive_erasing_peril/> It
may be the case that what both research teams are saying is that data
stored on the newfangled devices can't be reliably deleted or preserved
the way it can on magnetic media.
Researchers Graeme B. Bell and Richard Boddington, of Murdoch
University's School of IT, arrived at their findings by comparing the
way data is preserved on a 64GB Corsair P64 SSD versus an 80GB Hitachi
Deskstar hard drive. A PDF of their paper, which previously was
published in December in The Journal of Digital Forensics, Security and
Law, is here. <http://www.jdfsl.org/subscriptions/JDFSL-V5N3-Bell.pdf>
--
Regards
brd
Bernard Robertson-Dunn
Canberra Australia
email: brd at iimetro.com.au
website: www.drbrd.com
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