function mac256($b64_data, $key)
 {
     if (version_compare(PHP_VERSION, '5.1.2') < 0) {
         $result = hash_hmac4('sha256', $b64_data, $key, true);
     } else {
         $result = hash_hmac('sha256', $b64_data, $key, true);
         //(PHP 5 >= 5.1.2)
     }
     return $result;
 }
 function mac256($ent, $key)
 {
     if (PHP_VERSION_ID < 50102) {
         $res = hash_hmac4('sha256', $ent, $key, true);
     } else {
         $res = hash_hmac('sha256', $ent, $key, true);
         //(PHP 5 >= 5.1.2)
     }
     return $res;
 }