[Cryptography] Is there a good algorithm providing both compression and encryption at the same time?

[Lars Luthman]

On Wed, 2015-05-06 at 10:15 +0200, Francois BERENGER wrote: 
> I was thinking about something along those lines:
> 
> compression(clear_text) = (compression_dictionary, compressed_text)
> 
> then, instead of encrypting the whole resulting pair (to save some time),
> we would send over the wire
> 
> (symmetric_encrypt(compression_dictionary, secret_key), compressed_text)
> 
> Of course, I would like that the compressed_text cannot be uncompressed
> by someone who doesn't have access to the compression dictionary.

Wouldn't such an algorithm suffer from the same problem as using a block
cipher in ECB mode? That is, an attacker would be able to infer parts of
the structure of the plaintext by looking at repeated symbols in the
output (in this case compressed_text).

Assuming that different references in compressed_text to the same word
in compression_dictionary are recognisable as referring to the same word
for someone without access to the plaintext compression_dictionary, of
course. But if you are reasonably sure that they aren't you have
essentially encrypted compressed_text as well.


--ll
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