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Re: compression before encryption



On Thu, 10 Dec 1998, Jerome Etienne wrote:

> but in fact the compression increases the encryption scheme, because
> it reduces the redondancy of the plain text which is so usefull for
> cryptanalysis.
> did i miss something ?

Note that there is actually very few known about the usage of
cryptanalysis of the today's block ciphers with moderately reduntant
sources. [BK98] does provide an evidence, that when using differentially
weak ciphers, having only lot of ciphertexts is enough to find the key.
Examples were provided for 8-round DES and RC5. (I don't have the paper
atm so I may be wrong).

[BK98] Alex Biryukov, Eyal Kushilevitz, "From Differential Cryptanalysis
       to Ciphertext-Only Attacks", Proceedings of CRYPTO '98.

Helger
http://home.cyber.ee/helger



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