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Re: new hashes (SHA512, SHA3) in apt metadata and .changes files?

On Mon, Aug 05, 2013 at 01:33:24PM +0100, Ian Jackson wrote:
> AIUI SHA-512 is faster than SHA-256 on many processors, and not
> usually slower on the others.  If the hashes are too long, they can be
> truncated.

Not that, I think it matters, but this got me interested. It appears
that in practice this depends entirely on the word size. So SHA-256 is
faster on 32bit architectures and SHA-512 is faster on 64bit
architectures. The other aspect is that a block update of SHA-256 uses
64 rounds for a 64 byte block. Whereas SHA-512 uses 80 rounds for a 128
byte block update. So SHA-512 lowers the rounds/byte ratio. Now what can
we do with this knowledge? Probably negligible.


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