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RNGCryptoServiceProvider Class

Updated: March 2009

Implements a cryptographic Random Number Generator (RNG) using the implementation provided by the cryptographic service provider (CSP). This class cannot be inherited.

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

'Declaration
<ComVisibleAttribute(True)> _
Public NotInheritable Class RNGCryptoServiceProvider _
	Inherits RandomNumberGenerator
'Usage
Dim instance As RNGCryptoServiceProvider

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. 
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

System.Object
  System.Security.Cryptography.RandomNumberGenerator
    System.Security.Cryptography.RNGCryptoServiceProvider

This type is thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0

Date

History

Reason

March 2009

Added Thread Safety section.

Information enhancement.

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