[dm-crypt] Detecting the use of a keyfile

Arno Wagner arno at wagner.name
Thu May 23 19:36:33 CEST 2013

On Thu, May 23, 2013 at 07:13:03PM +0200, sector9 at ftml.net wrote:
> Understood. The problematic nature of claiming plausible deniability
> with regard to a lost non-existent keyfile comes down to extralegal
> practices and testimony on behalf of the user.

Indeed. Or legal practices where the police or prosecution
has a lot of leeway and when they think you are "difficult" 
they can bring the hammer down. Completely unethical of course,
but entirely legal. 

Remember that any form of authorities traditionally had the 
purpose to make the subjects do what the ruling class wanted, 
typically by threat of force. Laws were not about what is right, 
but about what behaviours were undesired by those in power. This 
still shows and by my impression some western countries are 
again strongly going in that direction, e.g. by calling people 
"terrorists" more and more frequently to take the rights away 
they would have had as mere murderers. 

> On the technical side, if done properly, one could place the boot
> partition on a separate USB and claim it is lost along with the keyfile.
> This setup would allow one to perfectly conceal whether or not one is
> using a keyfile and therefore provide plausible deniability about access
> to an encrypted system.
> The good old xkcd depiction of the reality of rubberhose cryptanalysis
> is so eloquent in its simplicity. 

Indeed. The message could not be clearer. Some XKCDs are
prue genius. 

> Yet we explore sidechannel attacks,
> social engineering, etc to bolster the use of the strong crypto ciphers.
> This variety of defense that I was inquiring about is another
> possibility to explore.
> I appreciate your answers very much.

You are very welcome. It is a discussion that needs
revisiting from time to time as things change. And there
is a lot of change currently.

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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