[dm-crypt] SSD disks and cryptsetup-reencrypt

Matthias Schniedermeyer ms at citd.de
Thu Jun 13 01:43:22 CEST 2013


On 13.06.2013 00:30, Arno Wagner wrote:
> 
> That said, unless you have high-resource attackers to defend
> against, with something like, say, 8 complete-disk re-encryptions
> you should be relatively secure. But don't blame me if it turns
> out you are not.

Or use one of the newer SSDs that take "the easy way" for secure 
erasing.

At last one or more of the current generation controller chips encrypt 
the contents by default (even without enabling FDE), as the controller 
has to do some form of scrambling anyway as high-entrophy is better for 
the flash cells(*). So at least one does AES256 encryption always. When 
you secure erase such a SSD they typically just generate a new key and 
not actually erase the flash-cells. The unknown is if they "drop" the 
old key in a secure way, but if they do there is no way to decrypt older 
content even if you desolder the flash-chips.

Also you have to have to hope that key generation is really random. That 
is something that can't really be proven (only disproven), so personally 
that is not something i could rely on. So i classify it as a "nice to 
have", if it works it is a line of defense otherwise it is "nothing".

Problem is i can't remember which one(s) do(es) that, and it's bed time.
:-)


*:
Something about preventing long streams of zeros, ones or both.


-- 

Matthias


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