public function encrypt($data)
    {
        if ($this->iv === null) {
            $dataEncrypted = mcrypt_encrypt($this->cipher, $this->key, $data, $this->mode);
        } else {
            $dataEncrypted = mcrypt_encrypt($this->cipher, $this->key, $data, $this->mode, $this->iv);
        }

        return bin2hex($dataEncrypted);
    }