Windows Forms: Encryption and Decryption using RC4 in C#

To play the demo, you can drag the textbox, label and button from the visual studio toolbox into your winform, then you can design a simple UI that allows you to encrypt and decrypt a string using the RC4 algorithm as shown below.

You can see the picture below, to see how the rc4 algorithm works.

The output byte is selected by looking up the values of S(i) and S(j), adding them together modulo 256, and then looking up the sum in S, S(S(i) + S(j)) is used as a byte of the key-stream, K.

OK, Now we will implement the RC4 algorithm in c# by creating an RC4 method to encrypt your data using RC4 algorithm as shown below.

public string RC4(string input, string key)
{
    StringBuilder result = new StringBuilder();
    int x, y, j = 0;
    int[] box = new int[256];
    for (int i = 0; i < 256; i++)
        box[i] = i;
    for (int i = 0; i < 256; i++)
    {
        j = (key[i % key.Length] + box[i] + j) % 256;
        x = box[i];
        box[i] = box[j];
        box[j] = x;
    }
    for (int i = 0; i < input.Length; i++)
    {
        y = i % 256;
        j = (box[y] + j) % 256;
        x = box[y];
        box[y] = box[j];
        box[j] = x;
        result.Append((char)(input[i] ^ box[(box[y] + box[j]) % 256]));
    }
    return result.ToString();
}

RC4 algorithm performs encryption and decryption in c# with key. So you can ddd code to the Encrypt button click event as the following c# code.

private void btnEncrypt_Click(object sender, EventArgs e)
{
    txtEncrypt.Text = RC4(txtInput.Text, "123");
}

Finally, Add code to the Decrypt button

private void btnDecrypt_Click(object sender, EventArgs e)
{
    txtDecrypt.Text = RC4(txtEncrypt.Text, "123");
}

You can also use the RC4 algorithm to encrypt and decrypt password using c# code.