Data Protection API

System.Security.Cryptography.ProtectedData

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

using System;
using System.Collections;
using System.Security.Cryptography;
using System.Text;

public class DataProtectionSample
{
  // Create byte array for additional entropy when using Protect method
  static byte[] _additionalEntropy = { 9, 8, 7, 6, 5 };

  public static void Main()
  {
    //Original data
    string secret = "Magic";
    PrintValues("The original data is:", secret);

    //Convert to bytes
    byte[] secretInBytes = Encoding.UTF8.GetBytes(secret);
    PrintValues("The original data in bytes is:", secretInBytes);

    //Encrypt the bytes
    byte[] encryptedSecret = Protect(secretInBytes);
    PrintValues("The encrypted byte array is:", encryptedSecret);

    // Decrypt the bytes
    byte[] originalDataInBytes = Unprotect(encryptedSecret);
    PrintValues("The original data in bytes is:", originalDataInBytes);

    //Convert to string
    string originalData = Encoding.UTF8.GetString(originalDataInBytes);
    PrintValues("The original data is:", originalData);
  }

  public static byte[] Protect(byte[] data)
  {
    // Encrypt the data using DataProtectionScope.CurrentUser. 
    // The result can be decrypted only by the same current user.
    return ProtectedData.Protect(data, _additionalEntropy, DataProtectionScope.CurrentUser);
  }

  public static byte[] Unprotect(byte[] data)
  {
    //Decrypt the data using DataProtectionScope.CurrentUser.
    return ProtectedData.Unprotect(data, _additionalEntropy, DataProtectionScope.CurrentUser);
  }

  public static void PrintValues(string header, IEnumerable detail)
  {
    Console.WriteLine(header);
    foreach (var item in detail) { Console.Write("\t{0}", item); }
    Console.WriteLine();
  }
}

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