I'm trying to make a file encryption and I really had no clue how to do it with RC4 with these code , text encryption and decryption are fine. button1 is for text encryption and button3 is for text decryption. The problem comes when I tried to encrypt an image. button2 is use to open and encrypt/decrypt a file
private void button1_Click(object sender, EventArgs e)
{
RC4 rc4 = new RC4(txtPassword.Text, txtText.Text);
txtHexDump.Text = RC4.StrToHexStr(rc4.EnDeCrypt());
}
private void button2_Click(object sender, EventArgs e)
{
openFileDialog1.Title = "Open Word or Text File";
openFileDialog1.Filter = "All Files (*.*)|*.*";
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
RC4 rc4 = new RC4(txtPassword.Text, Encoding.UTF32.GetString(GetBytesFromFile(openFileDialog1.FileName)));
SaveFileDialog saveFileDialog1 = new SaveFileDialog();
saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
saveFileDialog1.FilterIndex = 2;
saveFileDialog1.RestoreDirectory = true;
Stream mystream;
if (saveFileDialog1.ShowDialog() == DialogResult.OK)
{
if ((mystream = saveFileDialog1.OpenFile()) != null)
{
StreamWriter wText = new StreamWriter(mystream);
wText.Write(rc4.EnDeCrypt());
mystream.Close();
}
}
}
}
public static byte[] GetBytesFromFile(string fullFilePath)
{
// this method is limited to 2^32 byte files (4.2 GB)
FileStream fs = null;
try
{
fs = File.OpenRead(fullFilePath);
byte[] bytes = new byte[fs.Length];
fs.Read(bytes, 0, Convert.ToInt32(fs.Length));
return bytes;
}
finally
{
if (fs != null)
{
fs.Close();
fs.Dispose();
}
}
}
private void saveFileDialog1_FileOk(object sender, CancelEventArgs e)
{
}
private void button3_Click(object sender, EventArgs e)
{
RC4 rc4 = new RC4(txtPassword.Text, txtHexDump.Text);
rc4.Text = RC4.HexStrToStr(txtHexDump.Text);
txtText.Text = rc4.EnDeCrypt();
}
}
these are the encryption code I took from google
public class RC4
{
private const int N = 256;
private int[] sbox;
private string password;
private string text;
public RC4(string password, string text)
{
this.password = password;
this.text = text;
}
public RC4(string password)
{
this.password = password;
}
public string Text
{
get { return text; }
set { text = value; }
}
public string Password
{
get { return password; }
set { password = value; }
}
public string EnDeCrypt()
{
RC4Initialize();
int i = 0, j = 0, k = 0;
StringBuilder cipher = new StringBuilder();
for (int a = 0; a < text.Length; a++)
{
i = (i + 1) % N;
j = (j + sbox[i]) % N;
int tempSwap = sbox[i];
sbox[i] = sbox[j];
sbox[j] = tempSwap;
k = sbox[(sbox[i] + sbox[j]) % N];
int cipherBy = ((int)text[a]) ^ k; //xor operation
cipher.Append(Convert.ToChar(cipherBy));
}
return cipher.ToString();
}
public static string StrToHexStr(string str)
{
StringBuilder sb = new StringBuilder();
for (int i = 0; i < str.Length; i++)
{
int v = Convert.ToInt32(str[i]);
sb.Append(string.Format("{0:X2}", v));
}
return sb.ToString();
}
public static string HexStrToStr(string hexStr)
{
StringBuilder sb = new StringBuilder();
for (int i = 0; i < hexStr.Length; i += 2)
{
int n = Convert.ToInt32(hexStr.Substring(i, 2),16);
sb.Append(Convert.ToChar(n));
}
return sb.ToString();
}
private void RC4Initialize()
{
sbox = new int[N];
int[] key = new int[N];
int n = password.Length;
for (int a = 0; a < N; a++)
{
key[a] = (int)password[a % n];
sbox[a] = a;
}
int b = 0;
for (int a = 0; a < N; a++)
{
b = (b + sbox[a] + key[a]) % N;
int tempSwap = sbox[a];
sbox[a] = sbox[b];
sbox[b] = tempSwap;
}
}
}
