[RC5] My contribution to RC5

Ganesh Sittampalam ganesh.sittampalam at magd.ox.ac.uk
Sat Apr 4 11:35:17 EST 1998


>     It is not unreasonable to assume that a concerted "real" crack 
>     against a ciphertext has the following information about the 
>     plaintext:
>     1) What cipher was used to encrypt
>     2) What the keylength is
>     3) What headers were used to encode (wrapped) the plaintext
>     4) Who sent it
>     5) Who was to receive it
>     6) What (classification, not detail) the message contains
>     
>     For most real communication, the important one of those is 3.  Since 
>     most headers have a well-defined format, non-compliant trial 
>     ciphertexts generated in brute-force decryption efforts indicate a 
>     failed attempt.  4 and 5 can also help you narrow down the legal 
>     character set for the plaintext.  6 gives keywords to search for in 
>     the trial plaintext.

If I wanted to send something secret, then as the final stage before encrypting
it, I would compress it into some format with no header information whatsoever.
How would you handle cracking that efficiently?

Ganesh
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ganesh.sittampalam at magd.ox.ac.uk
http://users.ox.ac.uk/~magd0688
Life is a terminal illness
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