Re(2): A GPG version of the PGPstealth program?

Andrew Marlow apm35@student.open.ac.uk
Wed Aug 29 22:08:02 2001


tftp@yahoo.com writes:

>--- Andrew Marlow <apm35@student.open.ac.uk> wrote:
>>
>
>You can also XOR the GPG data with a text from a Bible.
>It would make an acceptable keystream for your purposes...
>even better than what you propose :-)
Not so. Take a look at the stealth web site for the technical details:- http://www.cypherspace.org/~adam/stealth/
>
>
>> This is the bit where I *deny* that there is a secret msg.
>
>The attacker can use the same algorithm - and your own
>public key as the secret key - to produce the GPG stream,
>which will prove that this is a GPG message.
I probably did not make myself clear enough. The idea is that the attacker is assumed to have knowledge of all steg methods so it is assumed that the attacker will do this. But when they do they just gets the stealth'd data which is DENIABLE.
>The number
>of stego algorithms is finite,
I do not believe in security thru obscurity (STO). Steg on its own is STO which doesn't work since the truth will always out in the end. My interest is in combining steg with deniable public key crypto.
>and if you want to get somewhere
>with this idea you probably have to use an outer envelope that
>can not be deciphered into anything but noise without the unique,
>secretly maintained, key.
The process of making the PGP/GPG stream resemble noise is what stealth is designed to do.
>
>
>You see, public key crypto and stego have opposite purposes. The
>PKI allows anyone to receive (and recognize them, of course!)
>crypto messages. Steganography systems go to great length to
>hide even the fact that there is a second message somewhere...
I agree ;-)
>
[snip]
>
>I am still unsure how valuable the second layer of encryption
>would be, especially using publicly available "secret" key...
The steg I would like to use employs a symmetric key, otherwise it would be very trivial STO. And we all know the trouble with symmetric key exchange. The people with whom I communicate in this way would be advised that the key is my public key, which adds a bit more obscurity to the STO but does not suffer the inconvenience of maintaining symmetric keys with all the people concerned.
>
>but if you really want to do that, there are plenty of simple
>ciphers, block or stream, that can be implemented in 100 lines
>of any language.
The strength of crypto lies in the strength of the algorithm and the key, and these are assessed by peer review. Thus I have no desire to (re)invent unproven crypto not subject to such review. There is plenty of strong crypto already out there. PGP/GPG is my favourite. I would use it. I would not invent my own.
>You only need to export the public key and
>then use it (all or portion of it) as a symmetric key.
>
>Dmitri
>
Regards, apm