[Nottingham] Can't remember the term for a cryptographic technique...

Roger Light roger at atchoo.org
Wed May 28 11:11:32 BST 2008


On Wed, May 28, 2008 at 09:44:34AM +0100, Joshua Lock wrote:
> On Wed, May 28, 2008 at 9:25 AM, Danny King <dannyking at gmail.com> wrote:
> > Hi all,
> >
> > A bit off topic so I apologise in advance:
> >
> > At the last meeting I was having a conversation with a few people and
> > we briefly touched on cryptography, specifically a certain area of it.
> > I can't for the life of me remember the term used to describe the
> > practice of encrypting a message so that two separate keys provide
> > different plaintexts when used on the same cyphertext i.e.:
> >
> > Alice creates a cyphertext from her secret message and gives Bob key1
> > and Fred key2. Bob uses key1 to decode the true message whilst Fred
> > uses key2 on the same cyphertext to decode a different but still
> > conceivable message.
> >
> > Can anyone help me to remember the name of this practice? I've been
> > googling and wikipeding for an hour with no success!
> 
> Hmm, not sure. Sounds a bit like it could be Steganography? What with
> the hidden messages and all.

Close, but no cigar. This sounds very similar to burglar alarm codes
where one code deactivates the alarm properly and another code
deactivates the alarm but alerts the police (or other agency) that
the code has been entered against the will of the person entering.

In the case of encryption, it gives plausible deniability.

So I'd try searching for "duress encryption" or something similar.
Given the powers of the government to require you disclose
encryption keys (iirc) based on RIPA, it might be worth including
that as well.

Cheers,

Roger



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