Re: Cryptographic Algorithm Metrics

[Kris Kennaway]

On Thu, Jan 04, 2001 at 01:23:30AM +0000, Paul Crowley wrote:
> Peter Fairbrother <[EMAIL PROTECTED]> writes:
> > Not so. Perfect compression with encryption works too.
> 
> Er, does it?  I get a 1k message from you, perfectly compressed and
> then encrypted with some strong algorithm and a 128-bit key.  As a
> godlike being unhindered by constraints of computational power, I try
> all 2^128 possible keys, and find due to the perfect compression that
> each of the 2^128 plaintexts is equally likely.

I think there's more that can be discovered here:

Decrypt the ciphertext with each possible key, and run it through the
perfect compression algorithm. If it compresses any more, then it's
not the plaintext since that is already perfectly compressed.

Kris

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