[RC5] What does finding the contest key prove?

Matthew_Webber at cca-int.com Matthew_Webber at cca-int.com
Fri Apr 16 21:35:24 EDT 1999


Not a bad idea, but two issues remain -

(1) What would this do to the time required to crack the key? My point was
that our present tests (where we know part of the plaintext) do not tell us
anything about the real-life time required to crack.

(2) I don't think your method would work if the text was not in English, or
was 'encrypted' using some very simple scheme (eg a->b, b->c, c->d etc)
before being put through DES or whatever.

Thanks

> Warning: this is from a layman's point of view:

> It wouldn't be too difficult to program a cracking application to run
> the encrypted text against each possible key and then bring the
> results that satisfy certain requirements to the operators attention.
>  Look for occurences in the decrypted text for common words like "
> computer ", " the ", " and ", " hello ", etc etc, and yes the extra
> spaces would help to make sure that you decrypted an actual word and
> not just a coincidental string of characters.  The number of hits on
> the common word list would provide for a way to quantify (or rank)
> how close the solution might be and then a person could look at it
> and make a determination.  The chances of a message decrypting and
> hitting the interesting level without being the actual decrypted text
> AND being any where near actually interesting to a human would be
> pretty low.


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