private void btnEncyrpt_Click(object sender, EventArgs e)
{
rsa.Gen_PublicKey(BigInteger.Parse(txt_P_val.Text), BigInteger.Parse(txt_Q_val.Text));
string plain = txtPlainText.Text;
byte[] dataToEncrypt = Encoding.ASCII.GetBytes(plain);
rsa.Encyrpt(dataToEncrypt);
txtCipherText.Text = rsa.cipherText;
}