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[liberationtech] CryptoParty Handbook

Eugen Leitl eugen at
Thu Oct 4 23:33:34 PDT 2012

On Fri, Oct 05, 2012 at 05:43:46AM +0200, Maxim Kammerer wrote:

> Did anyone try this with devices that are supposed to be resistant to
> file shredding due to wear leveling? I tried the following on two USB

Wear levelling is a function of newer devices (your old
USB flash sticks are unlikely to have it, but your new
SSD definitely has) and it hides damaged blocks 
transparently by using the overprovisioned flash
block pool (its size depending on on whether consumder or
enterprise drive, the latter having more overprovisioning). 

It might be possible to access the damaged blocks
via a debug function, or by flashing the drive
with custom firmware.

> keys, one ~12 years old, another ~6 years old, both formatted as
> FAT32:
> echo test_string_123 > x
> for i in $(seq 20); do cat x x > x1; mv x1 x; done
> cp x /media/... && sync
> shred -u /media/... && sync
> cp /dev/sd... image
> LC_ALL=C grep -wc test_string_123 image
> The result was 0 in both cases.

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