private void btencoding_Click(object sender, EventArgs e)
{
    if (mbox.Text == "")
    {
        MessageBox.Show("加密文字信息不能為空！");
        return;
    }
    if (publickey.Text == "")
    {
        MessageBox.Show("請生成公鑰！");
        return;
    }
    try
    {
        string pubKey = publickey.Text;
        byte[] mw = ASCIIEncoding.ASCII.GetBytes(mbox.Text);
        RSACryptoServiceProvider crypt = new RSACryptoServiceProvider();
        crypt.FromXmlString(pubKey);

        mw = crypt.Encrypt(mw, false);
        string encryttext = Convert.ToBase64String(mw);//加密后的結果怎樣處理解決顯示亂碼問題
        cbox.Text = encryttext;
    }
    catch
    {
        MessageBox.Show("請檢查是否打開公匙或者公匙是否損壞！");
    }
}

private void btdecoding_Click(object sender, EventArgs e)
{
    if (cbox.Text == "")
    {
        MessageBox.Show("請生成密鑰！");
        return;
    }
    try
    {
        RSACryptoServiceProvider crypt = new RSACryptoServiceProvider();
        byte[] bytes = Convert.FromBase64String(cbox.Text);//從密文框中取出的字符串正確處理才能解密
        string prtKey = privatekey.Text;
        crypt.FromXmlString(prtKey);
        byte[] decryptbyte = crypt.Decrypt(bytes, false);
        string decrypttext = Encoding.Default.GetString(decryptbyte);

        mbox.Text = decrypttext;
    }
    catch (CryptographicException ex)
    {
        //MessageBox.Show("請檢查是否打開私匙或者私匙是否損壞！");
        MessageBox.Show(ex.ToString());
    } if (cbox.Text == "")
    {
        MessageBox.Show("請生成密鑰！");
        return;
    }
}