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[liberationtech] secure wipe of flash memory

Michael Rogers michael at briarproject.org
Mon Jul 30 04:01:29 PDT 2012


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On 21/07/12 18:02, Chris Ball wrote:
> Hi,
> 
> On Sat, Jul 21 2012, Michael Rogers wrote:
>> Does anyone on the list know whether flash controller chips use 
>> journalling? I'm guessing they might because YAFFS does.
> 
> I don't think so -- YAFFS is a filesystem, and the wear-leveling 
> algorithm on the controller only knows how to act on reads/writes 
> to individual blocks on the flash, so they're very different
> layers. The flash controller isn't a replacement for a filesystem;
> you still need to use one, and it may or may not be journaled.
> 
> (Although the independence between wear-leveling algorithm and 
> filesystem isn't total; there's evidence that the vendors teach 
> their firmware how to handle writes to the Windows FAT cleanly.)

Thanks for the information Chris. Perhaps journalling was the wrong
word for me to use - what I'm interested in is whether a forensic
investigator can (partially) reconstruct the order in which the
logical blocks of a flash device were updated. If so, TrueCrypt hidden
volumes could be exposed.

Each time YAFFS updates a logical block, it stores a numbered mapping
from the logical block to a physical block. The numbers reveal the
order of the updates. Do you know whether controller chips do
something similar?

Cheers,
Michael
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