[RC5] An idea to prevent cheating

Alexander Kruppa alexander.kruppa at stud.tu-muenchen.de
Mon Aug 31 15:20:45 EDT 1998


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
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?


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