DTI White Paper on Export Control

[Greg Rose]

David Swarbrick writes:
>What PGP does also, is to demonstrate the intellectual dishonesty of
>trying to split off digital signatures and associated guaranteeing
>functions, from encryption functions. In these matters there are always
>mathematical complications, but in principle the one is merely the
>reverse use of sender and receivers keys. Systems which complicate this
>seem designed merely to split off the 'nice' certification from the
>'nasty' privacy.

This is not really the case. Of all practical public key cryptosystems 
(and most of the impractical ones) the RSA system is the only one which 
has the symmetry property, where the same key/algorithm can produce both 
digital signatures and encrypted contents. PGP wanted to avoid RSA for 
intellectual property reasons, so they chose a variant of the 
unencumbered ElGamal encryption (which they IMHO miscall Diffie-Hellman) 
and the Digital Signature Standard for signatures. But given the state of 
the art, if you are avoiding RSA, you are stuck with separate keys for 
encryption and signatures. (I know, if you want to get picky, it is 
possible to reuse the keys for the other functions, but in all cases you 
compromise security and/or significantly increase hassle.)

Many people (myself included) think that this separation is not a bad 
thing. After all, this means you can keep your "signature" key constant 
while rolling over (and discarding) old encryption keys. They have no 
justification for recovering your signature key. I think Adam Back has 
already given many of the justifications for this approach... if PGP 
supported it implicitly, I think it is a good idea. Not for key recovery 
reasons, though.

>Perhaps we should all make a declaration that we are posting from within
>the UK, and promise to unsubscribe if we travel abroad, just to keep the
>DTI happy.

And what made you think only Britons subscribe to this list?

regards,
Greg

Greg Rose                                     INTERNET: ggr@qualcomm.com
QUALCOMM Australia        VOICE:  +61-2-9181 4851   FAX: +61-2-9181 5470
Suite 410, Birkenhead Point              http://people.qualcomm.com/ggr/ 
Drummoyne NSW 2047      B5 DF 66 95 89 68 1F C8  EF 29 FA 27 F2 2A 94 8F