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MaskGenerationMethod Class
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MaskGenerationMethod Class

Represents the abstract class from which all mask generator algorithms must derive.

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

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class MaskGenerationMethod
'Usage
Dim instance As MaskGenerationMethod

Derived classes of MaskGenerationMethod compute masks that are used in key exchange algorithms such as Optimal Asymmetric Encryption Padding (OAEP).

This class is used by implementations of key exchange algorithms only for mask generation. Application code does not use this class directly.

The following code example demonstrates how to derive from the MaskGenerationMethod class.

Imports System
Imports System.Security.Cryptography

Public Class MaskGenerator
    Inherits System.Security.Cryptography.MaskGenerationMethod

    Private HashNameValue As String 

    ' Initialize a mask to encrypt using the SHA1 algorithm. 
    Public Sub New()
        HashNameValue = "SHA1" 
    End Sub 

    ' Create a mask with the specified seed. 
    Public Overrides Function GenerateMask( _
        ByVal seed() As Byte, _
        ByVal maskLength As Integer) As Byte()

        Dim hash As HashAlgorithm
        Dim rgbCounter(4) As Byte
        Dim targetRgb(maskLength) As Byte
        Dim counter As Integer 

        For inc As Int16 = 0 To targetRgb.Length
            ConvertIntToByteArray(counter + 1, rgbCounter)
            hash = CType( _
                CryptoConfig.CreateFromName(HashNameValue), _
                HashAlgorithm)
            Dim temp(4 + seed.Length) As Byte
            Buffer.BlockCopy(rgbCounter, 0, temp, 0, 4)
            Buffer.BlockCopy(seed, 0, temp, 4, seed.Length)
            hash.ComputeHash(temp)

            If (targetRgb.Length - inc > hash.HashSize / 8) Then
                Buffer.BlockCopy( _
                    hash.Hash, 0, targetRgb, inc, hash.Hash.Length)
            Else
                Buffer.BlockCopy( _
                    hash.Hash, 0, targetRgb, inc, targetRgb.Length - inc)
            End If

            inc += hash.Hash.Length
        Next 

        Return targetRgb
    End Function 

    ' Convert the specified integer to the byte array. 
    Private Sub ConvertIntToByteArray( _
        ByVal sourceInt As Integer, _
        ByRef targetBytes() As Byte)
        Dim remainder As Integer 
        Dim inc As Int16 = 0

        ' Clear the array prior to filling it.
        Array.Clear(targetBytes, 0, targetBytes.Length)

        While (sourceInt > 0)
            remainder = sourceInt Mod 256
            targetBytes(3 - inc) = CType(remainder, Byte)
            sourceInt = (sourceInt - remainder) / 256
            inc = inc + 1
        End While 
    End Sub 
End Class 

Public Class Form1
    Inherits System.Windows.Forms.Form

    ' Event handler for Run button. 
    Private Sub Button1_Click( _
        ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click

        tbxOutput.Cursor = Cursors.WaitCursor
        tbxOutput.Text = "" 

        Dim seed() As Byte = {&H1, &H2, &H3, &H4}
        Dim length As Int16 = 16
        Dim maskGenerator As New MaskGenerator
        Dim mask() As Byte = maskGenerator.GenerateMask(seed, length)

        tbxOutput.AppendText("Generated the following mask:")
        tbxOutput.AppendText(System.Text.Encoding.ASCII.GetString(mask))

        ' Align interface and conclude application.
        tbxOutput.AppendText(vbCrLf + "This sample completed" + _
            "successfully; press Exit to continue.")

        tbxOutput.Cursor = Cursors.Default
    End Sub 
    ' Event handler for Exit button. 
    Private Sub Button2_Click( _
        ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button2.Click

        Application.Exit()
    End Sub
#Region " Windows Form Designer generated code " 

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call 

    End Sub 

    'Form overrides dispose to clean up the component list. 
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then 
            If Not (components Is Nothing) Then
                components.Dispose()
            End If 
        End If 
        MyBase.Dispose(disposing)
    End Sub 

    'Required by the Windows Form Designer 
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer 
    'It can be modified using the Windows Form Designer.   
    'Do not modify it using the code editor. 
    Friend WithEvents Panel2 As System.Windows.Forms.Panel
    Friend WithEvents Panel1 As System.Windows.Forms.Panel
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Button2 As System.Windows.Forms.Button
    Friend WithEvents tbxOutput As System.Windows.Forms.RichTextBox
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.Panel2 = New System.Windows.Forms.Panel
        Me.Button1 = New System.Windows.Forms.Button
        Me.Button2 = New System.Windows.Forms.Button
        Me.Panel1 = New System.Windows.Forms.Panel
        Me.tbxOutput = New System.Windows.Forms.RichTextBox
        Me.Panel2.SuspendLayout()
        Me.Panel1.SuspendLayout()
        Me.SuspendLayout()
        
        'Panel2 
        
        Me.Panel2.Controls.Add(Me.Button1)
        Me.Panel2.Controls.Add(Me.Button2)
        Me.Panel2.Dock = System.Windows.Forms.DockStyle.Bottom
        Me.Panel2.DockPadding.All = 20
        Me.Panel2.Location = New System.Drawing.Point(0, 320)
        Me.Panel2.Name = "Panel2" 
        Me.Panel2.Size = New System.Drawing.Size(616, 64)
        Me.Panel2.TabIndex = 1
        
        'Button1 
        
        Me.Button1.Dock = System.Windows.Forms.DockStyle.Right
        Me.Button1.Font = New System.Drawing.Font( _
            "Microsoft Sans Serif", _
            9.0!, _
            System.Drawing.FontStyle.Regular, _
            System.Drawing.GraphicsUnit.Point, _
            CType(0, Byte))
        Me.Button1.Location = New System.Drawing.Point(446, 20)
        Me.Button1.Name = "Button1" 
        Me.Button1.Size = New System.Drawing.Size(75, 24)
        Me.Button1.TabIndex = 2
        Me.Button1.Text = "&Run" 
        
        'Button2 
        
        Me.Button2.Dock = System.Windows.Forms.DockStyle.Right
        Me.Button2.Font = New System.Drawing.Font( _
            "Microsoft Sans Serif", _
            9.0!, _
            System.Drawing.FontStyle.Regular, _
            System.Drawing.GraphicsUnit.Point, _
            CType(0, Byte))
        Me.Button2.Location = New System.Drawing.Point(521, 20)
        Me.Button2.Name = "Button2" 
        Me.Button2.Size = New System.Drawing.Size(75, 24)
        Me.Button2.TabIndex = 3
        Me.Button2.Text = "E&xit" 
        
        'Panel1 
        
        Me.Panel1.Controls.Add(Me.tbxOutput)
        Me.Panel1.Dock = System.Windows.Forms.DockStyle.Fill
        Me.Panel1.DockPadding.All = 20
        Me.Panel1.Location = New System.Drawing.Point(0, 0)
        Me.Panel1.Name = "Panel1" 
        Me.Panel1.Size = New System.Drawing.Size(616, 320)
        Me.Panel1.TabIndex = 2
        
        'tbxOutput 
        
        Me.tbxOutput.AccessibleDescription = _
            "Displays output from application." 
        Me.tbxOutput.AccessibleName = "Output textbox." 
        Me.tbxOutput.Dock = System.Windows.Forms.DockStyle.Fill
        Me.tbxOutput.Location = New System.Drawing.Point(20, 20)
        Me.tbxOutput.Name = "tbxOutput" 
        Me.tbxOutput.Size = New System.Drawing.Size(576, 280)
        Me.tbxOutput.TabIndex = 1
        Me.tbxOutput.Text = "Click the Run button to run the application." 
        
        'Form1 
        
        Me.AutoScaleBaseSize = New System.Drawing.Size(6, 15)
        Me.ClientSize = New System.Drawing.Size(616, 384)
        Me.Controls.Add(Me.Panel1)
        Me.Controls.Add(Me.Panel2)
        Me.Name = "Form1" 
        Me.Text = "MaskGenerationMethod" 
        Me.Panel2.ResumeLayout(False)
        Me.Panel1.ResumeLayout(False)
        Me.ResumeLayout(False)

    End Sub

#End Region
End Class 

' This sample produces the following output: 

' Generated the following mask:~&*(uj98U(*UD989D 
' This sample completedsuccessfully; press Exit to continue.

System.Object
  System.Security.Cryptography.MaskGenerationMethod
    System.Security.Cryptography.PKCS1MaskGenerationMethod

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be 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

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

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