Large Primes

[Brian Gladman]

From: "Owen Lewis" <oml@sysrx.uk.com>
To: <ukcrypto@chiark.greenend.org.uk>
Sent: Sunday, August 18, 2002 2:31 PM
Subject: RE: Large Primes


[snip]
> > Just my opinion, and Brian's point about something completely unknown
> > turning up is very relevant. I for one can't predict the future! We're
all
> > guessing here.
>
> That's the point, isn't it? What ever the unquantifiable risk in using any
> cipher, the use of a current PK cryptosystem *increases* it.

And vice versa:

"whatever the unquantifiable risk in using any PK cipher, the use of a
current symmetric cryptosystem *increases* it".

If we don't have any measures of strength for the two ciphers being
composed, it is impossible to predict which one of the pair will let us
down.

On the other hand, if we have a theory for the strength of asymmetric and
symmetric ciphers we can then choose either cipher to be much stronger than
the other so that the strength of the composed cipher is effectively that of
the weaker one of the pair.

And this might be either cipher depending on the choice we make.

   Brian Gladman