[rc5] rc5 crack schemes
gindrup at okway.okstate.edu
Mon Aug 25 12:12:41 EDT 1997
You are probably right that there are effective and subtle methods
to prune the likely search keyspace. I think neural netes would be
good at guessing likely candidates but that doesn't preclude them
guessing the entire keyspace in some convoluted order only to arrive
at the correct key just as the entire keyspace is exhausted...
Further, I thought the RC5 effort wasn't about tricky techniques
that would only work for this encryption technique. I thought it was
about proving that it isn't too hard to brute-force a decrypt of *any*
56bit-key encryption. Because, hey, if a couple thousand geeks
running in their spare time can crack it in something approaching
reasonable time, dedicated budgets and hardware can do *much* better.
I'd be more interested in bumping up the client so that it checks
two or three structurally similar keys at once. The sort of thing
where the rotate sequence doesn't alter much between decrypts using
two different keys. Probably though, the computational effort to find
such similar sets of keys would be prohibitive and representing the
sets would be "hard".
-- Eric Gindrup ! gindrup at Okway.okstate.edu
______________________________ Reply Separator _________________________________
Subject: [rc5] rc5 crack schemes
Author: <rc5 at llamas.net> at SMTP
Date: 1997/08/25 11:53
how about a variation on brute-force?
We shouldn't be doing a purely sequential scan, but using a bisection
At the very least, I think that we should assign blocks from both ends
of the keyspace, and go sequentially from there, instead of starting at
Also, there are some other schemes. The military uses a scheme which can
crack a lesser generation 128-bit crypt in approx. 25 minutes. (the gov
thinks only the US mil has this technology so it likes the DES-56 for
I've heard that it uses some sort of neural net + fuzzy logic in
determining key probabilities, and testing the keys that are calculated
to have a high probability of being correct.
Am I right or dead wrong?
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