[RC5] Cracking 40 bits in realtime

gindrup at okway.okstate.edu gindrup at okway.okstate.edu
Thu Jan 8 16:02:02 EST 1998


     [personal mail manually replied to the mailing list because, again, 
     this has something to do with distributed decryption.]
     
     Credit card packets have fixed headers in the first couple of bytes.  
     So do most other transmission data streams.  Compressed data has 
     compression headers.  Encryption encapsulated TCP/IP has encrypted 
     TCP/IP headers.  It is very rare to run into an encrypted message that 
     doesn't have some sort of trivially recognizable header in the 
     plaintext.  HTML and CGI messages have this property.  SSL packets 
     have this property.  (SMTP) e-Mail has this property.
     
     Very little that someone would want to capture and attack does not 
     have this property.
            -- Eric Gindrup ! gindrup at Okway.okstate.edu


______________________________ Reply Separator _________________________________
Subject: Re: [RC5] Cracking 40 bits in realtime 
Author:  "Christopher Hodson (Consultant)" <cmh at fpk.hp.com>  at SMTP
Date:    1/8/98 4:19 PM


gindrup at okway.okstate.edu wrote:
> 
>      Anyone making a serious attack on a message already _does_ know 
>      something about what it contains.
     
I agree entirely, however, just because you know that there is a credit 
card number 10 bytes in does NOT mean you can otimize a client as much 
as bovine has done.  It would take much longer in practice.
     
I'm just playing devil's advocate here. 
--
Christopher M. Hodson
System Admin (Consultant)
Hewlett Packard Engineering Services Group 
cmh at fpk.hp.com
     


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