David A. Harding on 21 May 2009 10:55:56 -0700

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Re: [PLUG] Does appending known information to a key compromise its hash?

On Thu, May 21, 2009 at 12:26:26PM -0400, K.S. Bhaskar wrote:
> [A]ppending a known (to an attacker) string to an unknown key doesn't
> reduce the randomness in the key. The counter argument is that if the
> [...] hash has [...] known bits [...], [it] is more easily broken.

It follows logically that hashes with known parts are more easily broken
than hashes without known parts in flawed hash functions. In unflawed
hash functions, if such exists, or in hash functions where the attacker
doesn't know of any flaws, the avalanche effect[1] ensures the unknown
parts remain secret.

    [1] http://en.wikipedia.org/wiki/Avalanche_effect

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