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3DES

The DES algorithm has been around for a long time, and the 56-bit version is now easily crackable (in less than a day on fairly modest equipment). An enhancement, and one which is still fairly compatible with DES, is the 3-DES algorithm. It has three phases, and splits the key into two. Overall the key size is typically 112 bits (with a combination of the three keys - of which two of the keys are the same). The algorithm is EncryptK3( DecryptK2( EncryptK1(message), where K1 and K3 are typically the same (to keep compatibility). [Lecture][Tutorial]

In this case, if we try "test" as the key we get:

"Specified key is a known weak key for 'TripleDES' and cannot be used." and it will not encrypt.

As a test: "Hello how are you?" with a stronger key of "m65hhhgfd"  which should give:

B8841E83139EDF87AE0D033162CFE174A968ED820FA86C01

The code is:

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections;
using System.Security.Cryptography;
using System.IO;
using System.Text;

public partial class _Default5 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        try
        {
            TripleDES threedes = new TripleDESCryptoServiceProvider();

            threedes.Key = StringToByte(this.tbKey.Text, 24); // convert to 24 characters - 192 bits
            threedes.IV = StringToByte("12345678");
            byte[] key = threedes.Key;
            byte[] IV = threedes.IV;

            ICryptoTransform encryptor = threedes.CreateEncryptor(key, IV);

            MemoryStream msEncrypt = new MemoryStream();
            CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);

            // Write all data to the crypto stream and flush it.
            csEncrypt.Write(StringToByte(this.tbMessage.Text), 0, StringToByte(this.tbMessage.Text).Length);
            csEncrypt.FlushFinalBlock();

            // Get the encrypted array of bytes.
            byte[] encrypted = msEncrypt.ToArray();

            this.tbEncrypt.Text = ByteToString(encrypted);

            ICryptoTransform decryptor = threedes.CreateDecryptor(key, IV);

            // Now decrypt the previously encrypted message using the decryptor
            MemoryStream msDecrypt = new MemoryStream(encrypted);
            CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read);

            this.tbDecrypt.Text = ByteToString(csDecrypt);
        }
        catch (Exception ex)
        {
            this.tbEncrypt.Text = ex.Message.ToString();
        }
    }
    public static byte[] StringToByte(string StringToConvert)
    {

        char[] CharArray = StringToConvert.ToCharArray();
        byte[] ByteArray = new byte[CharArray.Length];
        for (int i = 0; i < CharArray.Length; i++)
        {
            ByteArray[i] = Convert.ToByte(CharArray[i]);
        }
        return ByteArray;
    }
    public static byte[] StringToByte(string StringToConvert, int length)
    {

        char[] CharArray = StringToConvert.ToCharArray();
        byte[] ByteArray = new byte[length];
        for (int i = 0; i < CharArray.Length; i++)
        {
            ByteArray[i] = Convert.ToByte(CharArray[i]);
        }
        return ByteArray;
    }
    public static string ByteToString(CryptoStream buff)
    {
        string sbinary = "";
        int b = 0;
        do
        {
            b = buff.ReadByte();
            if (b != -1) sbinary += ((char)b);

        } while (b != -1);
        return (sbinary);
    }
    public static string ByteToString(byte[] buff)
    {
        string sbinary = "";
        for (int i = 0; i < buff.Length; i++)
        {
            sbinary += buff[i].ToString("X2"); // hex format
        }
        return (sbinary);
    }
}