Provably "Secure" Crypto
John Anonymous MacDonald
nobody at cypherpunks.ca
Tue Nov 26 09:43:14 PST 1996
At 4:18 AM 11/26/1996, Peter M Allan wrote:
>> Which part of this have you failed to understand? Look in section 5.3.1
>> of Volume 3 of "The Art of Computer Programming" by Knuth. You will find
>> there a rigorous proof that the "information theoretic lower bound" of
>> an algorithm which sorts by comparison of keys is O(nlg(n)).
>That is a bound on a _reliable_ algorithm. A faster one is to shuffle
>the elements and present it as sorted. Lightning fast, but only with
>low probability of correctness. That is what we are up against in a key
>search attack. The other guy just might guess my 100 bit key first time,
>millionth time or whatever - early enough anyway.
>So to get a lower bound you have to show that a lucky guess cannot be
>distinguished from an unlucky one - and if you do that without a one
>time pad I take my hat off.
If the chance of a successful guess is absurdly low, the algorithm can
be considered to be secure. It is quite unlikely that you will guess
a random 128-bit key. Hence, you could have a secure algorithm in
which a successful guess can be distinguished from an unsuccessful
one.
diGriz
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