[rc5] Some thoughts on finding the key

Jeff Woods jeff at delta.com
Fri Oct 24 11:02:38 EDT 1997


At 09:45 PM 10/23/97 -0500, you wrote:

>The client only compares the first 8 bytes of the decrypted text to 
>the known plaintext.  The algorithm encrypts/decrypts in multiples of 
>8 bytes, so there's no benefit to doing a smaller comparison.  

I thought this was RC5-32/12/??, or 32-bit wordsize.   It SHOULD decrypt in
FOUR byte chunks, no?  Or did I miss something in reading the RFC?  Of
course, you're the expert....  I was more concerned with the algorithm to
compare those 4 or 8 byte chunks to "The " and "The unkn"....   Compares
are usually the SLOWEST things one can do in computing other than floating
point emulation, and since Cyberian's clients are faster than ours, I was
thinking of this as the most likely area for optimization.   I assume the
coders have run a profiler on this thing to find out where most of the time
is spent?


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