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Date: Wed, 3 Dec 2014 10:54:22 -0500
From: Peter Chapin <PChapin@vtc.vsc.edu>
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Subject: Re: The enormous potential that programming LaTeX in Ada presents.
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Xref: news.eternal-september.org comp.lang.ada:23839
Date: 2014-12-03T10:54:22-05:00
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On Wed, 3 Dec 2014, Denis McMahon wrote:

> So, it should not matter whether your plaintext is 7 bit ascii, a 
> picture, a compressed zip archive of the cia's darkest secrets or Malia 
> Obamas twitter account, if you run these through a good encryption 
> algorithm an attacker should be unable to tell, even in possession of 
> the encryption and decryption algorithms, what the format of the source 
> data was, or even how long it was (but it's reasonable to deduce it's no 
> longer than the ciphertext).

In many applications of cryptography the plaintext is compressed before it 
is encrypted so, in fact, it is fairly common for the plaintext to be 
longer than the ciphertext.

This is done because the compression "randomizes" the statistics of the 
data input to the encryption algorithm and can make the encryption harder 
to defeat... even if the attacker knows the compression has occurred and 
what compression algorithm was used.

Peter