Date: Wed, 3 Oct 2012 16:01:35 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: crypt() non-DES support * Gregor Pintar <grpintar@...il.com> [2012-10-03 13:56:37 +0200]: > 2012/10/3, Szabolcs Nagy <nsz@...t70.net>: > > * Daniel Cegie?ka <daniel.cegielka@...il.com> [2012-10-03 09:16:02 +0200]: > >> We already have SHA3 finalist: > >> > >> http://csrc.nist.gov/groups/ST/hash/sha-3/winner_sha-3.html > >> http://keccak.noekeon.org/ > >> http://keccak.noekeon.org/KeccakReferenceAndOptimized-3.2.zip > >> > > > > note that crypt is a password based key derivation function > > that is supposed to be (configurably) slow, protected against > > dictionary attacks and collision resistant (used for password > > verification mostly), while sha* is a secure hash that is > > supposed to be fast and collision resistant (used for integrity > > protection and digital signatures mostly) > > > > You can increase number of rounds. well the main selling point of keccak is that it has very simple and efficient hw implementation which means hw implementation can be a lot faster than any software implementation on a generic cpu this is good for a cryptographic hash, because you want it to be fast, but it's bad for a passwd hash, because you want it to have stable run time, otherwise you cannot set a reasonable iteration count (eg for this reason the scrypt passwd hash was designed so that hw implementation would use lots of transistors and cannot gain much performance) (the nist pbkdf2 often uses hmac-sha hash internally but it's main application is creating a secure symmetric encryption key from a simple password, the stored passwd hash application is more sensitive to the speed variation of the hash function) tl;dr: don't use sha3 for passwd hash
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