Re: [VOTE] Hash_pbkdf2

Hey all, The voting phase has ended for hash_pbkdf2, and it has passed with a vote of 8:0. I've moved the RFC into Accepted state, and will merge the PR today into master, then move the RFC into Implemented. Thanks! Anthony On Mon, Jul 2, 2012 at 10:37 PM, Sara Golemon <pollita@php.net> wrote: > > > On Mon, Jul 2, 2012 at 5:49 PM, Anthony Ferrara <ircmaxell@gmail.com>wrote: > >> Sara, >> >> On Mon, Jul 2, 2012 at 8:24 PM, Sara Golemon <pollita@php.net> wrote: >> > I'd like to see hash_init() support this mode as well (for >> completeness). >> > Perhaps something like the following: >> > >> > $ctx = hash_init("sha512", HASH_PBKDF2, $salt, array('length' >> > => 32, >> > 'iterations' => 5000)); >> > >> > The new fourth parameter being an overloadable options generic so that >> we >> > don't have an endless list of parameters for all the possible hashing >> types. >> >> The only problem that I have with this sort of implementation is that >> the only way it would work is to buffer the entire input (each >> hash_update call), and run it all at the end. That's because the data >> (password) is used in every iteration, so there's no pre-computation >> that can be done. And at that point, what's the benefit to it? >> >> public function pbkdf2($algo, $password, $salt, $iterations, $length) { >> $size = getHashBlockSize($hash); >> $len = ceil($length / $size); >> $result = ''; >> for ($i = 1; $i <= $len; $i++) { >> $tmp = hash_hmac($hash, $salt . pack('N', $i), $password, >> true); >> $res = $tmp; >> for ($j = 1; $j < $iterations; $j++) { >> $tmp = hash_hmac($hash, $tmp, $password, true); >> $res ^= $tmp; >> } >> $result .= $res; >> } >> return substr($result, 0, $length); >> } >> >> Contrast that to a normal hash function (used by the current >> hash_init) which iterates over blocks of input, and once it's done >> with a block, it doesn't need it anymore (which is where using >> something like hash_init/hash_update can make sense on large input). >> >> Additionally, hmac only uses the message in a single hash, so it can >> be streamed in as well (pre-compute the earlier hashes/data, stream >> the intermediate hash, then hash the final one). >> >> So while it could be added (just make hash_update buffer into a >> context, then have hash_final actually run the derivation), I'm not >> sure it makes sense to add it there. >> >> Thoughts? >> >> Anthony >> > > Ah, wasn't clear on how pbkdf2 worked. Your argument makes total sense. > Thanks for explaining it. :) >