[RC5] First impressions

Mike Learn learnm at nationwide.com
Tue Mar 3 10:42:58 EST 1998


I came upon an interesting thought today.  I agree that the order in which  the
blocks are handed out should not matter.  However, it could be information that
could be used to a competitor's advantage.

Were I to embark upon my own key space brute force search for DESII, I would have
started at the top and gone down.  This would allow me to crunch more untouched
blocks.  If d.net were handing out blocks randomly, however, I would have a larger
chance of testing blocks that had already been checked and rejected.

I guess what I am trying to say is that my chances would be better if I knew the
order that d.net was checking.  It could be put to my advantage.  A couple days
before the end of the contest, I could pretty much say where the key wasn't (even
without crunching a single number myself!)

Jason Bechtel wrote:

> Paul Ross wrote:
>
>         As far as I know, the main keyspace is divided in to large "chunks."
> The large chunks are processed at random, but the actual blocks within
> each chunk are processed from start to finish, sequentially... for RC5
> at least.
>
> > averages are it'll be more towards the middle than either end...
>
>         Intuition deceives you.  If you've studied probability at all you know
> that this is not true.  Sorry...  :(
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