[RC5] An idea to prevent cheating

Dan Hrabarchuk danh at firstwest.com
Tue Sep 1 10:58:30 EDT 1998


But how much time whould it take to calc the checksum? Just a little sure
but can we throw out 3% of dnet?
-----Mensaje original-----
De: Alexander Kruppa <alexander.kruppa at stud.tu-muenchen.de>
Para: rc5 at lists.distributed.net <rc5 at lists.distributed.net>
Fecha: Monday, August 31, 1998 3:48 PM
Asunto: [RC5] An idea to prevent cheating


Hi,

I just recalled all the trouble with Bitbucket because some people
thought they were cheating in the DES-II-1 contest, and I thought about
what could be done to prevent cheating. It is rather obvious, actually.
This is the idea I got: we could simply compute a "checksum" over all
the trial encryption results the client gets while he tries to find the
right key. I.e. if the client is working on block 123456:00000000
compute
des(kp,123456:00000000) xor des(kp,123456:00000001) xor ...
(kp is the known plaintext) and store the result it in the output block.
If there is any doubt that a person or team processes the blocks
properly, the blocks could be redone on a trusted machine and the
checksums could be compared.
I don´t see any way how this check could be worked around by a cheater.
You only get the correct checksum by computing the encrypted string for
all keys. It should help soften the paranoia in some people, and maybe
then we could finally release the block data structure if we are sure
that it won´t tempt people into cheating?

Ciao,
  Alex.

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