Rijndael

System.Security.Cryptography.RijndaelManaged

Namespace: System.Security.Cryptography
Assembly: mscorlib (in mscorlib.dll)

using System;
using System.IO;
using System.Security.Cryptography;

namespace RijndaelManaged_Example
{
  class RijndaelExample
  {
    public static void Main()
    {
      try
      {
        string original = "Here is some data to encrypt!";

        using (RijndaelManaged myRijndael = new RijndaelManaged())
        {
          byte[] encrypted = EncryptStringToBytes(original, myRijndael.Key, myRijndael.IV);
          string roundtrip = DecryptStringFromBytes(encrypted, myRijndael.Key, myRijndael.IV);

          Console.WriteLine("Original:   {0}", original);
          Console.WriteLine("Round Trip: {0}", roundtrip);
        }
      }
      catch (Exception e)
      {
        Console.WriteLine("Error: {0}", e.Message);
      }
    }

    static byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV)
    {
      if (string.IsNullOrEmpty(plainText)) throw new ArgumentNullException("plainText");
      if (Key == null || Key.Length <= 0) throw new ArgumentNullException("Key");
      if (IV == null || IV.Length <= 0) throw new ArgumentNullException("Key");

      byte[] encrypted;

      using (RijndaelManaged rijAlg = new RijndaelManaged())
      {
        rijAlg.Key = Key;
        rijAlg.IV = IV;

        ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV);

        using (MemoryStream msEncrypt = new MemoryStream())
        using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
        {
          using (StreamWriter swEncrypt = new StreamWriter(csEncrypt)) 
            swEncrypt.Write(plainText);
         
          encrypted = msEncrypt.ToArray();
        }
      }

      return encrypted;
    }

    static string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
    {
      if (cipherText == null || cipherText.Length <= 0) throw new ArgumentNullException("cipherText");
      if (Key == null || Key.Length <= 0) throw new ArgumentNullException("Key");
      if (IV == null || IV.Length <= 0) throw new ArgumentNullException("Key");

      string plaintext;

      using (RijndaelManaged rijAlg = new RijndaelManaged())
      {
        rijAlg.Key = Key;
        rijAlg.IV = IV;

        ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);

        using (MemoryStream msDecrypt = new MemoryStream(cipherText))
        using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
        {
          plaintext = srDecrypt.ReadToEnd();
        }
      }

      return plaintext;
    }
  }
}

Taken from MSDN: http://msdn.microsoft.com/en-us/library/system.security.cryptography.rijndaelmanaged.aspx

Source:  http://stevenhollidge.com/blog-source-code/RijndaelExample.zip