Rijndael (/AES)

AES (or Rijndael) is the new replacement for DES, and uses 128-bit blocks with 128, 192 and 256 bit encryption keys. It was selected by NIST in 2001 (after a five year standardisation process). The name Rijndael comes from its Belgium creators: Joan Daemen and Vincent Rijmen. The key has an IV and a key element, where the IV gives the overall key some variation. In this case the key is 256 bits, and the IV is 128 bits. [Lecture][Tutorial]

Message
Encryption key:


Encrypted	Decrypted

In this case, if we try "test" as the key, and test message of: "This is a test message" which should get:

54A6B8A846B61EFBFD258AF2B1E7BF129A24545CAEDC315DA1D3F924E4AA2F00

Also, a key of "test" with a message of "test" gives:

AECC52950EFC49F6B2B2407ECEE65FE5

which is 32 characters, and thus relates to 128 bits, which is the block size (as "test" fits into a single block). All our outputs will thus be a multiple of 32 hex characters.

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
        { 
            Rijndael myRijndael = new RijndaelManaged();
          

            myRijndael.Key = StringToByte(this.tbKey.Text, 32); // convert to 32 characters - 256 bits
            myRijndael.IV = StringToByte("0123456789ABCDEF"); // 16 chars for IV

            byte[] key = myRijndael.Key;
            byte[] IV = myRijndael.IV;

            ICryptoTransform encryptor = myRijndael.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 = myRijndael.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);
    }
}