Re: Collision resistant encryption scheme

Paul Rubin <http://phr.cx@NOSPAM.invalid> writes:

>Unruh <unruh-spam@physics.ubc.ca> writes:
>> Ie, if you found such a scheme, so that for no two keys any collisions
>> existed, you would have a weak encryption scheme.

>The question allowed for the possibility of a collision, and only
>asked for bounds on the probability. As DAW noted, it sounds like a
>homework problem. Real-world systems generally don't look like that.

"I need a
scheme that is resistant to such collisions. Probably there are exist
sufficient conditions that can guarantee that such plaintext does not
exist and the scheme is collision resistant?"

Actually all shift cyphers (Caesar cyphers) have this feature.
Ie, C(R,M)=M+R mod(2^blocklength) have the property that for every R (the key)
C(R,M)!= C(R',M)
Received on Tue Feb 7 21:00:08 2006