// Use this code if the mhash library isn't compiled in PHP


function hmac ($key, $data)

{
   // RFC 2104 HMAC implementation for php.
   // Creates an md5 HMAC.
   // Eliminates the need to install mhash to compute a HMAC
   // Hacked by Lance Rushing
   $b = 64; // byte length for md5
   if (strlen($key) > $b) {
       $key = pack("H*",md5($key));
   }
   $key  = str_pad($key, $b, chr(0x00));
   $ipad = str_pad('', $b, chr(0x36));
   $opad = str_pad('', $b, chr(0x5c));
   $k_ipad = $key ^ $ipad ;
   $k_opad = $key ^ $opad;
   return md5($k_opad  . pack("H*",md5($k_ipad . $data)));
}