Simple implementation of hmac sha1
<?php
function hmac_sha1($key, $data)
{
// Adjust key to exactly 64 bytes
if (strlen($key) > 64) {
$key = str_pad(sha1($key, true), 64, chr(0));
}
if (strlen($key) < 64) {
$key = str_pad($key, 64, chr(0));
}
// Outter and Inner pad
$opad = str_repeat(chr(0x5C), 64);
$ipad = str_repeat(chr(0x36), 64);
// Xor key with opad & ipad
for ($i = 0; $i < strlen($key); $i++) {
$opad[$i] = $opad[$i] ^ $key[$i];
$ipad[$i] = $ipad[$i] ^ $key[$i];
}
return sha1($opad.sha1($ipad.$data, true));
}