note 92684 deleted from function.hash-hmac by googleguy

Note Submitter: Henry Merriam ---- <?php /** * Implementation of the PBKDF2 key derivation function as described in RFC 2898. * * PBKDF2 was published as part of PKCS #5 v2.0 by RSA Security. The standard is * also documented in IETF RFC 2898. * * The first four function arguments are as the standard describes: * * PBKDF2(P, S, c, dkLen) * * The fifth function argument specifies the hash function to be used. This should * be provided in the same format as used for the hash() function. The default * hash algorithm is SHA-1, but this is not recommended for new applications. * * The function returns false if dk_len is too large. Otherwise it returns the * derived key as a binary string. * * @author Henry Merriam <php@henrymerriam.com> * * @param string p password * @param string s salt * @param int c iteration count * @param int dk_len derived key length (octets) * @param string algo hash algorithm * * @return string derived key */ function pbkdf2($p, $s, $c, $dk_len, $algo = 'sha1') { // experimentally determine h_len for the algorithm in question static $lengths; if (!isset($lengths[$algo])) { $lengths[$algo] = strlen(hash($algo, null, true)); } $h_len = $lengths[$algo]; if ($dk_len > (pow(2, 32) - 1) * $h_len) { return false; // derived key is too long } else { $l = ceil($dk_len / $h_len); // number of derived key blocks to compute $t = null; for ($i = 1; $i <= $l; $i++) { $f = $u = hash_hmac($algo, $s . pack('N', $i), $p, true); // first iterate for ($j = 1; $j < $c; $j++) { $f ^= ($u = hash_hmac($algo, $u, $p, true)); // xor each iterate } $t .= $f; // concatenate blocks of the derived key } return substr($t, 0, $dk_len); // return the derived key of correct length } } ?>