ExcludingRNG.cs

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

namespace APress.DotNetSecurity.Chapter2.ExcludingRNG
{
 class ExcludingRNGTester
 {
  static void Main(string[] args)
  {
   try
   {
    byte[] randomExcludedData = new byte[255];
    byte[] excludedData = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
    Console.WriteLine("Excluded bytes are " +
     ArrayToHexString(excludedData));
    Console.WriteLine("Creating the FineGrainedRNG instance...");
    FineGrainedRNG fng = new ExcludingRNG();
    Console.WriteLine("Getting the excluded random bytes...");
    fng.GetBytes(randomExcludedData, excludedData);
    Console.WriteLine("Random bytes are " +
     ArrayToHexString(randomExcludedData));
   }
   catch(CryptographicUnexpectedOperationException cuoe)
   {
    Console.WriteLine("CryptographicUnexpectedOperationException:  "
     + cuoe.Message);
    Console.WriteLine(cuoe.StackTrace);
   }
   catch(CryptographicException ce)
   {
    Console.WriteLine("CryptographicException:  " + ce.Message);
    Console.WriteLine(ce.StackTrace);
   }
   catch(Exception ge)
   {
    Console.WriteLine("Exception:  " + ge.GetType().Name + " " + ge.Message);
    Console.WriteLine(ge.StackTrace);
   }
   finally
   {
    Console.WriteLine("Press the return key to continue...");
    Console.Read();
   }
  }
  private static String ArrayToHexString(byte[] ByteData)
  {
   StringBuilder retVal = new StringBuilder();
   
   foreach(byte b in ByteData)
   {
    retVal.Append(b.ToString("X2"));
    retVal.Append(" ");
   }
   retVal.Remove(retVal.Length - 1, 1);

   return retVal.ToString();
  } 
 }

 public interface FineGrainedRNG
 {
  void GetBytes(byte[] data, byte[] excludedValues);
 }

 public class ExcludingRNG : RNGCryptoServiceProvider, FineGrainedRNG
 {
  public ExcludingRNG() : base()
  {
  }
 
  public void GetBytes(byte[] data, byte[] excludedValues)
  {
   if(null != excludedValues && excludedValues.Length > 0)
   {
    byte[] tempData = {1};

    for(int i = 0; i < data.Length; i++)
    {
     do
     {
      base.GetBytes(tempData);
     } while (Array.IndexOf(excludedValues, tempData[0]) >= 0);
    
     data[i] = tempData[0];
    }
   }
   else
   {
    throw new ArgumentException("The excludedValues argument is invalid.");
   }
  }
 }
}