[dm-crypt] Detecting the use of a keyfile

Arno Wagner arno at wagner.name
Thu May 23 16:55:12 CEST 2013

On Thu, May 23, 2013 at 03:27:25PM +0200, sector9 at ftml.net wrote:
> During the boot stage is it possible for an attacker with physical
> access to detect if a keyfile is used to unlock an encrypted volume?

Yes, very easily. Just look at the initrd or init-script that does it.
Booting with a USB/CD Linux (e.g. Knoppix) makes this easy, including
the test whether the keyfile is valid.
> Does it yield to protest that the keyfile is lost/unknown/destroyed when
> in reality there is no keyfile but instead a regular non-keyfile
> passphrase?

Aehm, what are you asking? Whether you could lie about the former
presence of a keyfile and claim the data is now inacessible due
to its absence? That depends very much so how much technological
knowledge those have that should believe it and what mechnism for
its loss or destruction you propose. Also, keyfiles are not
secure, so you would have to justify the low securuity level and
the absebce of backups as well.

Generally, I would call it a losing strategy.

Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
There are two ways of constructing a software design: One way is to make it
so simple that there are obviously no deficiencies, and the other way is to
make it so complicated that there are no obvious deficiencies. The first
method is far more difficult.  --Tony Hoare

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