[RC5] Win32 GUI client on Cyrix - Slow or normal ?

gindrup at okway.okstate.edu gindrup at okway.okstate.edu
Thu Jan 29 15:11:17 EST 1998


     1) A pair of DES keys is checked faster than a pair of RC5 keys.
     2) The default DES block is larger than the default RC5 block.
     
     Now, a little discussion:
     First, check the FAQ.  Links are in the Help File section of 
     http://www.distributed.net/des/
     
        Next, I say a pair of DES keys because each DES key has a buddy.  
     If you decrypt with the key, you can decrypt with the buddy much 
more 
     easily.  I posted a lengthy discussion of this a week or two ago.  
RC5 
     keys don't come in "correlated" pairs, so decrypting a pair of RC5 
     keys is just as hard as decrypting each member of the pari 
separately.
        The clients take advantage of this property of DES keys to do two 
     keys at a time.  This is one of the reasons that the keyrates are so 
     much higher wth the new clients.
     
        The default DES block is four times larger than a default RC5 
     block.  Thus, if you can do one DES pair in the time it takes to do 
     one RC5 key, then it still takes four times as long to do the block.
        Blocks don't have buddy pairs in them because it is very easy to 
     compute the buddy key of a key *and*, in fact, you don't ever have 
to 
     explicitly compute the buddy key.  The client can just report that 
     "key x and its buddy didn't crack the code" and then it's up to the 
     keyservers to compute the buddy explicitly.
        Thus, if you get a 2^30 block, your machine will effectively test 
     2^31 keys.  Half of them will be buddies of the keys in the block.  
     The block, however, is four times larger than an RC5 block and so, 
by 
     our wild approximation, will take four times longer to do.
     
        Your number was 18 minutes for RC5.  Multiplying by four gives 1 
     hour 12 minutes.  This isn't hours and hours, so either you've 
     exaggerated a little, you're downloading blocks larger than 2^30, 
I've 
     overestimated the relative speeds of your machines on RC5 versus 
DES, 
     or there is something competing for processing time on your 
machines.  
        Any and possibly all of these could be the case.
            -- Eric Gindrup ! gindrup at Okway.okstate.edu


______________________________ Reply Separator 
_________________________________
Subject: [RC5] Win32 GUI client on Cyrix - Slow or normal ?   
Author:  <rc5 at llamas.net > at SMTP
Date:    1998/01/29 02:22


My Cyrix P166+ cracked RC5 blocks in about 18 minutes. The new DESII 
Win32 GUI clients takes hours and hours to crack a DESII block.
     
Are these blocks so much bigger, or is something wrong (I thought DES 
was supposed to go faster dan RC5).
     
--
Rogier
     
theroge at xs4all.nl
http://www.xs4all.nl/~theroge
     
     
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