public function encrypt(array $params = [])
    {
        $requestString = '';
        $requestKey = $this->params['request_keys'];
        for ($i = 0, $n = strlen($requestKey); $i < $n; ++$i) {
            $char = $requestKey[$i];
            if (!isset($this->encryptData[$char])
              || !isset($params[$this->encryptData[$char]])) {
                continue;
            }
            $requestString .= $params[$this->encryptData[$char]];
        }

        return sha1($requestString);
    }