[Cryptography] coding for compression or secrecy or both or neither

Dennis E. Hamilton dennis.hamilton at acm.org
Thu Jan 22 12:42:35 EST 2015

 -- replying below to --
From: cryptography [mailto:cryptography-bounces+dennis.hamilton=acm.org at metzdowd.com] On Behalf Of Henry Baker
Sent: Tuesday, January 20, 2015 20:48
To: cryptography at metzdowd.com
Subject: Re: [Cryptography] coding for compression or secrecy or both or neither

Re compressible ciphertexts:

[ ... ]

The usual reason for preferring uncompressible ciphertext is that it potentially maximizes the bit rate, but if bit rate isn't the most pressing problem, then other goals can be given priority.

   I think for me uncompressible ciphertext is also an "indistinguishable from random" indicator.  But the point is made.
   If I base64-encode a binary ciphertext for some practical purpose, it is compressible but there is no information disclosure beyond what there would be if I had the binary ciphertext.  
   The per-byte entropy might matter in other situations where apparent randomness is a requirement, but not in the ciphertext case being discussed here.

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