Using PBKDF2 with Kohana 3 Auth Module

application_classes_auth.php

<?php

	abstract class Auth extends Kohana_Auth {


		public function hash ( $str ) {
			if ( ! $this->_config['hash_key'] )
				throw new Kohana_Exception( 'A valid hash key must be set in your auth config.' );

			if ( 'pbkdf2' == $this->_config['hash_method'] ) {
				return base64_encode( self::pbkdf2( 
					$str, 
					$this->_config['hash_key'], 
					Arr::get( $this->_config['pbkdf2'], 'rounds', 1000 ),
					Arr::get( $this->_config['pbkdf2'], 'length', 45 ),
					Arr::get( $this->_config['pbkdf2'], 'method', 'sha256' )
				) );
			}
			else {
				return parent::hash( $str );
			}
		}

		/** PBKDF2 Implementation (described in RFC 2898)
		 *
		 *  @param string p password
		 *  @param string s salt
		 *  @param int c iteration count (use 1000 or higher)
		 *  @param int kl derived key length
		 *  @param string a hash algorithm
		 *
		 *  @return string derived key
		 *
		 *  @url http://www.itnewb.com/tutorial/Encrypting-Passwords-with-PHP-for-Storage-Using-the-RSA-PBKDF2-StandardL
		*/
		public static function pbkdf2 ( $p, $s, $c, $kl, $a = 'sha256' ) {
		 
				$hl = strlen(hash($a, null, true)); # Hash length
				$kb = ceil($kl / $hl);              # Key blocks to compute
				$dk = '';                           # Derived key
		 
				# Create key
				for ( $block = 1; $block <= $kb; $block ++ ) {
		 
						# Initial hash for this block
						$ib = $b = hash_hmac($a, $s . pack('N', $block), $p, true);
		 
						# Perform block iterations
						for ( $i = 1; $i < $c; $i ++ )
		 
								# XOR each iterate
								$ib ^= ($b = hash_hmac($a, $b, $p, true));
		 
						$dk .= $ib; # Append iterated block
				}
		 
				# Return derived key of correct length
				return substr($dk, 0, $kl);
		}

	}

application_config_auth.php

<?php defined('SYSPATH') or die('No direct access allowed.');

	return array(
		'driver'       => 'orm',
		'hash_method'  => 'pbkdf2',
		'hash_key'     => 'zomg',
		'lifetime'     => 1209600,
		'session_key'  => 'auth_user',
		'pbkdf2'       => array(
			'method'  => 'sha256',
			'rounds'  => 1000,
			'length'  => 45,
		)
	);