[RC5] Golomb Rulers (was "sexy" projects)

gindrup at okway.okstate.edu gindrup at okway.okstate.edu
Tue Mar 3 19:28:22 EST 1998

     For the former, I'm referring to a pre-print I have lying around 
     here somewhere.  I'll try to dig it up and get the author's 
     permission to quote more of it.
     For the latter, please review
     To represent the "march of progress", move each row, to the right of 
     the budget column up ~2.5 lines.
            -- Eric Gindrup ! gindrup at Okway.okstate.edu

______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: [RC5] Golomb Rulers (was "sexy" projects)  
Author:  <rc5 at llamas.net > at SMTP
Date:    3/3/98 11:53 PM

>     There is no result showing that the security of Triple-DES is any 
>     greater than DES.  As a previous note by myself pointed out, doing
>     an attack on an unknown ASCII message requires ~0.3% more effort to 
>     brute force than to crack a message with known preamble.
>     Anthough it has been shown that DES does not have a group structure, 
>     so Triple-DES is inequivalent to DES, it has not been shown that the 
>     encryption is any stronger.  Further, it is not (currently) thought 
>     likely that Triple-DES is as strong as its keylength would indicate.
I have a reasonable amateur's knowledge of cryptography, and have not seen 
any evidence at all that 3DES is not 112-bit strong.
>     Dual-DES has been shown to be equivalent to another encryption
>     scheme with 64-bit keys, so it's *very unlikely* that Triple-DES 
>     gets you more than an equivalent of 72-bits of encryption.
2DES is equivalent in complexity to DES, provided that you have storage for 
2^56 blocks (encrypt two known plaintexts with each of the 2^56 possible 
keys, sort the list so you can check if a block's in the list in constant 
time, decrypt two ciphertexts with each possible key and check if the result 
is equal to any of the encrypted plaintexts; total time 2^58 encryptions to 
produce the list, 2^58 trial decryptions, for 2^59 work factor). To the best 
of my knowledge, there is no quicker attack on it.
>     It has been calculated that a direct attack on dedicated hardware 
>     could for ~US$10,000 break DES in a few minutes.
Not anywhere I've seen; it's almost impossible to get $10,000 worth of 
custom-made chips (minimum orders being a lot bigger), and, for an attack to 
take 2^9 seconds ('a few minutes'), you need 2^17 250MHz crackers. Not a 
$10,000 project by any means.
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