Re: Does good compression = good encryption?

Cameron Hutchison (camh@nospam.orthanc.apana.org.au)
Wed, 15 Nov 1995 16:32:18 +1000 (EST)

Once upon a time Dennis Clark said...
>
> A clearer way of saying that they "reduce redundancy" is to say that
> they increase the entropy (randomness) of a message.

I was going to say this too, but then I decided to look it up.
Compression does not increase the entropy of a message. The entropy is
related to the message; compression does not change the message, just
its representation. Also, entropy is the "amount of information" in
a message, not its randomness.

I found this info in Bruce Schneier's Applied Cryptography (1st ed.)
on page 189.

Cheers

-- 
Cameron Hutchison (camh@nospam.orthanc.apana.org.au) | Beware of the clams
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