One time pads

[Bill Stewart]

At 09:20 PM 10/16/2002 -0400, Sam Ritchie wrote:
>     ACTUALLY, quantum computing does more than just halve the effective key
>length. With classical computing, the resources required to attack a given
>key grow exponentially with key length. (a 128-bit key has 2^128
>possibilities, 129 has 2^129, etc. etc. you all know this...)
>     With quantum computing, however, the complexity of an attack grows only
>polynomially. Hence a MUCH MUCH more agreeable time frame for brute force
>attacks. Good stuff, eh?

The speed of quantum computing depends on the algorithm -
it's generally believed that for some problems, like factoring,
you can hypothetically get a hypothetically-precise-enough
quantum computer to resolve in polynomial time instead of exponential,
subject to a variety of caveats I don't pretend to understand,
but for many other problems they're only cutting the
effective number of bits in half (which is still exponentially
faster than brute-force, but not *enough* exponentially faster),
and for other problems they may not be a match at all.

So Peter Trei's assertion that it's really only a big impact
on asymmetric cryptosystems, and a much smaller impact on symmetric,
is one layer deeper description than yours,
and it's something that does still leave us with practical ways
to use cryptography that don't include briefcases and handcuffs.

Myself, I'd rather hang out at Delphi waiting for the
stoned babe to give out the correct answers....  :-)
         ("If you use the right key, a great kingdom will fall...")