<?php
# hmac_sha1.php - HMAC-SHA1 implementation
# Version 1.0
# ---------------------------------------- 
# Copyright (c) 2006 Dwayne C. Litzenberger <dlitz@dlitz.net>
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
# ---------------------------------------- 


# HMAC is:
#       H(K XOR opad, H(K XOR ipad, plaintext))
# where ipad is 0x36 repated B times, and opad is 0x5C repeated B times.
# B is the block length of the hash function (for SHA-1, B=64)
# Keys longer than B are hashed before being used.
#
# See "HMAC: Keyed-Hashing for Message Authentication" (RFC 2104)
#       http://www.ietf.org/rfc/rfc2104.txt
function hmac_sha1($data, $key, $raw_output=FALSE)
{
    $block_size = 64;   // SHA-1 block size
    
    if (strlen($key) > $block_size) {
        $k = pack("H*", sha1($key));
    } else {
        $k = str_pad($key, $block_Size, "\x00", STR_PAD_RIGHT);
    }
    
    $ki = '';
    for($i = 0; $i < $block_size; $i++) {
        $ki .= chr(ord(substr($k, $i, 1)) ^ 0x36);
    }
    $ko = '';
    for($i = 0; $i < $block_size; $i++) {
        $ko .= chr(ord(substr($k, $i, 1)) ^ 0x5C);
    }

    $h = sha1($ko . pack('H*', sha1($ki . $data)));
    if ($raw_output) {
        return pack('H*', $h);
    } else {
        return $h;
    }
}