decode encode php

function encode($string, $key = NULL) {
        if(!$key)
            $key = ENCRYPTION_KEY;
        $key = sha1($key);
        $strLen = strlen($string);
        $keyLen = strlen($key);
        $j = 0;
        $hash = "";
        for ($i = 0; $i < $strLen; $i++) {
            $ordStr = ord(substr($string, $i, 1));
            if ($j == $keyLen) {
                $j = 0;
            }
            $ordKey = ord(substr($key, $j, 1));
            $j++;
            $hash .= strrev(base_convert(dechex($ordStr + $ordKey), 16, 36));
        }
        $hash = $hash . "-" . md5($string);

        return $hash;
    }

    function decode($string, $key = NULL) {
      $hash = "";
      if(!empty($string)) {
        $strings = explode("-", $string);
        $string = $strings[0];
        if(!$key)
            $key = ENCRYPTION_KEY;
        $key = sha1($key);
        $strLen = strlen($string);
        $keyLen = strlen($key);
        $j = 0;
        $hash = "";
        for ($i = 0; $i < $strLen; $i+=2) {
            $ordStr = hexdec(base_convert(strrev(substr($string, $i, 2)), 36, 16));
            if ($j == $keyLen) {
                $j = 0;
            }
            $ordKey = ord(substr($key, $j, 1));
            $j++;
            $hash .= chr($ordStr - $ordKey);
        }

        //hash check
        if (md5($hash) != $strings[1])
            return "-";
      }
      return $hash;
    }