Re: Collision resistant encryption scheme

Unruh wrote:
> 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)

   Same for XOR, C(R,M)=M^R, a standard implementation of a One-Time Pad.

--Mike Amling
Received on Tue Feb 7 21:00:10 2006