public function decrypt($cipherText)
    {
        $cipherText = base64_decode($cipherText);
        $iv = substr($cipherText, 0, self::IV_SIZE);
        $cipherText = substr($cipherText, self::IV_SIZE);
        $token = mcrypt_decrypt(self::CIPHER, $this->key, $cipherText, self::MODE, $iv);
        return $token;
    }