Steve Sheldon

I was looking around for a piece of code which would take a string and encrypt it into a Base64 encoded string such that I could later decrypt the string and obtain the message.  This was to be used in a confirmation email.  The message being urlencoded onto a confirmation url that the user could click and verify his email address was correct, or to redirect to a password setup page.  I found some examples in MSDN, but none did quite what I wanted.  I also wanted to use the key from the machineKey section of web.config.

I came up with this and thought others might find some use for it.

using System;
using System.Text;
using System.Security.Cryptography;
using System.Web.Configuration;
using System.IO;
using System.Configuration;

namespace SodaBlue.Utility
{
  public static class Cryptography
  {
    public static string EncryptAESToBase64(string dataToEncrypt)
    {
      //Get the decryption key from the machine key section of the web.config
      MachineKeySection machineKey = (MachineKeySection)ConfigurationManager.GetSection("system.web/machineKey");
      string key = machineKey.DecryptionKey;
      byte[] keyBytes = UTF8Encoding.UTF8.GetBytes(key);
      Rfc2898DeriveBytes rfc = new Rfc2898DeriveBytes(key, keyBytes, 1000);

      // Use the AES managed encryption provider
      AesManaged encryptor = new AesManaged();
      encryptor.Key = rfc.GetBytes(16);
      encryptor.IV = rfc.GetBytes(16);

      using (MemoryStream ms = new MemoryStream())
      {
        using (CryptoStream encrypt = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
        {
          byte[] dataBytes = new UTF8Encoding(false).GetBytes(dataToEncrypt);
          encrypt.Write(dataBytes, 0, dataBytes.Length);
          encrypt.FlushFinalBlock();
          encrypt.Close();
          return Convert.ToBase64String(ms.ToArray());
        }
      }
    }

    public static string DecryptAESFromBase64(string dataToDeCrypt)
    {
      //Get the decryption key from the machine key section of the web.config
      MachineKeySection machineKey = (MachineKeySection)ConfigurationManager.GetSection("system.web/machineKey");
      string key = machineKey.DecryptionKey;
      byte[] keyBytes = new UTF8Encoding(false).GetBytes(key);
      Rfc2898DeriveBytes rfc = new Rfc2898DeriveBytes(key, keyBytes, 1000);

      AesManaged decryptor = new AesManaged();
      decryptor.Key = rfc.GetBytes(16);
      decryptor.IV = rfc.GetBytes(16);

      using (MemoryStream ms = new MemoryStream())
      {
        using (CryptoStream decrypt = new CryptoStream(ms, decryptor.CreateDecryptor(), CryptoStreamMode.Write))
        {
          byte[] dataBytes = Convert.FromBase64String(dataToDeCrypt);
          decrypt.Write(dataBytes, 0, dataBytes.Length);
          decrypt.FlushFinalBlock();
          decrypt.Close();

          return new UTF8Encoding(false).GetString(ms.ToArray());
        }
      }
    }

  }
}

And a simple unit test to validate we can encrypt and decrypt

using System;
using NUnit.Framework;
using sbCommunity.Core.Infrastructure;

namespace sbCommunity.UnitTests
{
  [TestFixture]
  public class CryptographyTest
  {
    [Test]
    public void TestEncrypt()
    {
      const string cTest = "Now is the time for all good men to come to the aid of our countries";
      string encrypted = Cryptography.EncryptAESToBase64(cTest);
      string decrypted = Cryptography.DecryptAESFromBase64(encrypted);
      Assert.AreEqual(cTest, decrypted);
    }
  }
}