[RC5] DES-II question
stephen at tgivan.com
Fri Mar 27 14:03:08 EST 1998
Ted Rathkopf wrote:
> > > > I was just curious - how many "false positives" were there during
> > > > DES-II contest? (I hope this information is not classified...)
> > We check the first 8 bytes.
> So, in 8 bytes there are 256^8 or 2^64 combinations of which 1 will be
> the correct combination of 8 bytes.
> DES uses a 56 bit key, so of the 2^56 keys, 1 will be the correct key.
> So, statistically, there should not have been ANY false positives.
> If my math is wrong, somebody please correct me.
Your math is correct. However, the client only compares the first 8
bytes of the message. So it is possible to have other keys that, by
chance, decrypt the first 8 bytes but don't decrypt the whole
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