building a true RNG (was: Quantum Computing ...)

[Paul Crowley]

daw at mozart.cs.berkeley.edu (David Wagner) writes:
> Eugen Leitl  wrote:
> >Is there any point in compressing the video before running it through a 
> >cryptohash?
> 
> No.  (assuming you're talking about lossless compression)
> 
> In general, any invertible transformation neither adds or subtracts
> entropy, and hence is extremely unlikely to make any difference to the
> performance of the hash function (assuming SHA-1 is cryptographically
> secure, which it is currently believed to be).  Lossless compression
> is just one special kind of invertible transformation.

There's no point as far as security is concerned, I agree - and
usually people are talking about lossy compression, which can only do
harm.  The argument seems to be that compression followed by hashing
will be faster than hashing alone, but that seems unikely to me.
-- 
  __  Paul Crowley
\/ o\ sig at paul.ciphergoth.org
/\__/ http://www.ciphergoth.org/

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