RNGCryptoServiceProvider.GetBytes(Byte[]) RNGCryptoServiceProvider.GetBytes(Byte[]) RNGCryptoServiceProvider.GetBytes(Byte[]) RNGCryptoServiceProvider.GetBytes(Byte[]) Method

Definition

Fills an array of bytes with a cryptographically strong sequence of random values.

public:
 override void GetBytes(cli::array <System::Byte> ^ data);
public override void GetBytes (byte[] data);
override this.GetBytes : byte[] -> unit
Public Overrides Sub GetBytes (data As Byte())
Parameters
data
Byte[]

The array to fill with a cryptographically strong sequence of random values.

Exceptions

The cryptographic service provider (CSP) cannot be acquired.

Examples

The following code example shows how to create a random number with the RNGCryptoServiceProvider class.

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

using namespace System;
using namespace System::IO;
using namespace System::Text;
using namespace System::Security::Cryptography;

ref class RNGCSP
{
public:
    // Main method.
    static void Main()
    {
        const int totalRolls = 25000;
        array<int>^ results = gcnew array<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);
        }
    }

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

    static Byte RollDice(Byte numberSides)
    {
        if (numberSides <= 0)
            throw gcnew ArgumentOutOfRangeException("numberSides");
        // Create a new instance of the RNGCryptoServiceProvider.
        RNGCryptoServiceProvider^ rngCsp = gcnew RNGCryptoServiceProvider();
        // Create a byte array to hold the random value.
        array<Byte>^ randomNumber = gcnew array<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;
    }
};

int main()
{
    RNGCSP::Main();
}
//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;
    }
}
'The following sample uses the Cryptography class to simulate the roll of a dice.
Imports System
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography



Class RNGCSP
    Private Shared rngCsp As New RNGCryptoServiceProvider()
    ' Main method.
    Public Shared Sub Main()
        Const totalRolls As Integer = 25000
        Dim results(5) As Integer

        ' Roll the dice 25000 times and display
        ' the results to the console.
        Dim x As Integer
        For x = 0 To totalRolls
            Dim roll As Byte = RollDice(System.Convert.ToByte(results.Length))
            results((roll - 1)) += 1
        Next x
        Dim i As Integer

        While i < results.Length
            Console.WriteLine("{0}: {1} ({2:p1})", i + 1, results(i), System.Convert.ToDouble(results(i)) / System.Convert.ToDouble(totalRolls))
            i += 1
        End While
        rngCsp.Dispose()
        Console.ReadLine()
    End Sub


    ' This method simulates a roll of the dice. The input parameter is the
    ' number of sides of the dice.
    Public Shared Function RollDice(ByVal numberSides As Byte) As Byte
        If numberSides <= 0 Then
            Throw New ArgumentOutOfRangeException("NumSides")
        End If 
        ' Create a byte array to hold the random value.
        Dim randomNumber(0) As Byte
        Do
            ' Fill the array with a random value.
            rngCsp.GetBytes(randomNumber)
        Loop While Not IsFairRoll(randomNumber(0), numberSides)
        ' Return the random number mod the number
        ' of sides.  The possible values are zero-
        ' based, so we add one.
        Return System.Convert.ToByte(randomNumber(0) Mod numberSides + 1)

    End Function


    Private Shared Function IsFairRoll(ByVal roll As Byte, ByVal numSides As Byte) As Boolean
        ' 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.
        Dim fullSetsOfValues As Integer = [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

    End Function 'IsFairRoll
End Class

Remarks

The length of the byte array determines how many cryptographically strong random bytes are produced.

This method is thread safe.

Applies to