RNGCryptoServiceProvider.GetBytes Method

//The following sample uses the Cryptography class to simulate the roll of a dice. 

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

class RNGCSP
{
    private static RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();
    // Main method. 
    public static void Main()
    {
        const int totalRolls = 25000;
        int[] results = new int[6];

        // Roll the dice 25000 times and display 
        // the results to the console. 
        for (int x = 0; x < totalRolls; x++)
        {
            byte roll = RollDice((byte)results.Length);
            results[roll - 1]++;
        }
        for (int i = 0; i < results.Length; ++i)
        {
            Console.WriteLine("{0}: {1} ({2:p1})", i + 1, results[i], (double)results[i] / (double)totalRolls);
        }
        rngCsp.Dispose();
        Console.ReadLine();
    }

    // This method simulates a roll of the dice. The input parameter is the 
    // number of sides of the dice. 

    public static byte RollDice(byte numberSides)
    {
        if (numberSides <= 0)
            throw new ArgumentOutOfRangeException("numberSides");

        // Create a byte array to hold the random value. 
        byte[] randomNumber = new byte[1];
        do
        {
            // Fill the array with a random value.
            rngCsp.GetBytes(randomNumber);
        }
        while (!IsFairRoll(randomNumber[0], numberSides));
        // Return the random number mod the number 
        // of sides.  The possible values are zero- 
        // based, so we add one. 
        return (byte)((randomNumber[0] % numberSides) + 1);
    }

    private static bool IsFairRoll(byte roll, byte numSides)
    {
        // There are MaxValue / numSides full sets of numbers that can come up 
        // in a single byte.  For instance, if we have a 6 sided die, there are 
        // 42 full sets of 1-6 that come up.  The 43rd set is incomplete. 
        int fullSetsOfValues = Byte.MaxValue / numSides;

        // If the roll is within this range of fair values, then we let it continue. 
        // In the 6 sided die case, a roll between 0 and 251 is allowed.  (We use 
        // < rather than <= since the = portion allows through an extra 0 value). 
        // 252 through 255 would provide an extra 0, 1, 2, 3 so they are not fair 
        // to use. 
        return roll < numSides * fullSetsOfValues;
    }
}