using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int key = 0;
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{//Encryption
String word = txt_encrypt.Text.ToUpper();
String encrypted = "";
key = Int32.Parse(txt_key.Text);
for (int l = 0; l <= word.Length-1;l++ )
{
int index = findLetter(word[l]);
int encryptionValue = (key * index + 3) % 26;
encrypted = encrypted + alphabet[encryptionValue];
}
txt_dcrypt.Text = encrypted;
}
public int findLetter(char s) {
for (int i = 0; i<=25;i++ )
{
if(alphabet[i]==s){
return i;
}
}
return 0;
}
private void button2_Click(object sender, EventArgs e)
{//Decryption
String word = txt_dcrypt.Text;
String decrypted = "";
for (int l = 0; l <= word.Length - 1; l++)
{
int index = findLetter(word[l]);
int inverse = findMinus(key);
int decryptionValue = (inverse*( index-3)) % 26;
decrypted = decrypted + alphabet[decryptionValue];
}
txt_encrpt1.Text = decrypted;
}
public int findMinus(int a) {
for (int i = 0; i <= 26;i++ )
{
if((a*i)%26 == 1){
return i;
}
}
return 0;
}
private void txt_encrpt1_TextChanged(object sender, EventArgs e)
{
}
}
}
