[RC5] DES-II question

Stephen Rasku 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
message.
--
To unsubscribe, send 'unsubscribe rc5' to majordomo at lists.distributed.net
rc5-digest subscribers replace rc5 with rc5-digest



More information about the rc5 mailing list