[21491] in cryptography@c2.net mail archive
RE: passphrases with more than 160 bits of entropy
daemon@ATHENA.MIT.EDU (Whyte, William)
Wed Mar 22 10:25:40 2006
X-Original-To: cryptography@metzdowd.com
X-Original-To: cryptography@metzdowd.com
Date: Wed, 22 Mar 2006 10:14:21 -0500
From: "Whyte, William" <WWhyte@ntru.com>
To: "Alexander Klimov" <alserkli@inbox.ru>,
<cryptography@metzdowd.com>
> BTW, with respect to entropy reduction is there any explanation why
> PBKDFs from PKCS5 hash
>=20
> password || seed || counter
>=20
> instead of
>=20
> counter || seed || password
>=20
> and thus reduce all the entropy of the password to the size of the
> internal state.
In theory it's more efficient, as it lets you precalculate
all but the last block of (password || salt). In practice,
this is one of the situations where efficiency helps the
attacker more than the implementer.
William
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