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MACTripleDES Class

Computes a Message Authentication Code (MAC) using TripleDES for the input data CryptoStream.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Class MACTripleDES
	Inherits KeyedHashAlgorithm
'Usage
Dim instance As MACTripleDES

/** @attribute ComVisibleAttribute(true) */ 
public class MACTripleDES extends KeyedHashAlgorithm
ComVisibleAttribute(true) 
public class MACTripleDES extends KeyedHashAlgorithm

A MAC can be used to determine whether a message sent over an insecure channel has been tampered with, provided that the sender and receiver share a secret key. The sender computes the MAC for the original data, and sends both as a single message. The receiver recomputes the MAC on the received message, and checks that the computed MAC matches the transmitted MAC.

Any change to the data or the MAC will result in a mismatch, because knowledge of the secret key is required to change the message and reproduce the correct MAC. Therefore, if the codes match, the message is authenticated.

MACTripleDES uses a key of length 16 or 24 bytes, and produces a hash sequence of length 8 bytes.

The following section contains code examples. The first example computes the MAC for data using the TripleDES hash algorithm and stores it in result. The second example demonstrates how to use each member of the MACTripleDES class.

Example #1

This example assumes that there is a predefined constant DATA_SIZE.

Dim data(DATA_SIZE) As Byte
Dim key(24) As Byte
       
Dim mac3des As New MACTripleDES(key)
       
Dim result As Byte() = mac3des.ComputeHash(data)

ubyte data[] = new ubyte[dataSize];
ubyte key[] = new ubyte[24];
MACTripleDES mac3des = new MACTripleDES(key);
ubyte result[] = mac3des.ComputeHash(data);

Example #2

Imports System
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography

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 = ""

        EncodeNothing()
        EncodeMessage()
        EncodeStream()

        tbxOutput.AppendText(vbCrLf + "This sample completed " + _
            "successfully; press Exit to continue.")
        tbxOutput.Cursor = Cursors.Default
    End Sub
    Private Sub EncodeNothing()
        Dim macTriple As New MACTripleDES

        macTriple.Initialize()

        Dim key(23) As Byte
        RandomNumberGenerator.Create().GetBytes(key)
        macTriple.Key = key
        
        Dim message(1023) As Byte
        macTriple.ComputeHash(message)
        SummarizeMAC(macTriple, "MACTripleDES after initialization.")
    End Sub
    ' Compute the hash for a MACTripleDES that has transformed a byte array.
    Private Sub EncodeMessage()
        Dim keyData(23) As Byte
        RandomNumberGenerator.Create().GetBytes(keyData)
        Dim macTriple As New MACTripleDES(keyData)
        Dim message As String = "Encoding is fun!"
        Dim encodedMessage() As Byte 
        encodedMessage = EncodeBytes(Encoding.ASCII.GetBytes(message))
        macTriple.ComputeHash(encodedMessage)

        SummarizeMAC(macTriple, "MACTripleDES after encoding a message.")
    End Sub
    ' Transform the byte array using MacTripleDES,
    ' and then summarize its properties.
    Private Function EncodeBytes(ByVal sourceBytes() As Byte)
        Dim currentPosition As Int16 = 0

        Dim targetBytes(1023) As Byte
        Dim sourceByteLength As Int16 = sourceBytes.Length

        ' Create an encryptor with a random key and the TripleDES
        ' class name.
        Dim key(23) As Byte
        RandomNumberGenerator.Create().GetBytes(key)
        Dim tripleDesName As String = "System.Security.Cryptography.TripleDES"
        Dim macTriple As New MACTripleDES(tripleDesName, key)

        ' Retrieve the block size to read the bytes.
        Dim inputBlockSize As Integer = macTriple.InputBlockSize

        Try
            ' Determine if multiple blocks can be transformed.
            If (macTriple.CanTransformMultipleBlocks) Then
                Dim numBytesRead As Int16 = 0

                While (sourceByteLength - currentPosition >= inputBlockSize)
                    ' Transform the bytes from the currentposition in the
                    ' sourceBytes array, writing the bytes to the 
                    ' targetBytes array.
                    numBytesRead = macTriple.TransformBlock( _
                        sourceBytes, _
                        currentPosition, _
                        inputBlockSize, _
                        targetBytes, _
                        currentPosition)

                    ' Advance the current position in the sourceBytes array.
                    currentPosition += numBytesRead
                End While

                ' Transform the final block of bytes.
                Dim finalBytes() As Byte = macTriple.TransformFinalBlock( _
                        sourceBytes, _
                        currentPosition, _
                        sourceByteLength - currentPosition)

                ' Copy the contents of the finalBytes array to the
                ' targetBytes array.
                finalBytes.CopyTo(targetBytes, currentPosition)
            End If
        Catch ex As Exception

            WriteLine("Caught unexpected exception:" + _
                    ex.ToString())
        End Try

        ' Determine if the current transform can be reused.
        If (Not macTriple.CanReuseTransform) Then
            ' Free up any used resources.
            macTriple.Clear()
        End If

        ' Find the length of valid bytes (those without zeros).
        Dim iEnum As System.Collections.IEnumerator
        iEnum = targetBytes.GetEnumerator()

        Dim i As Int16 = 0

        While (iEnum.MoveNext())
            If (iEnum.Current.ToString().Equals("0")) Then
                Exit While
            End If
            i = i + 1
        End While

        ' Compute the hash based on the valid bytes in the array.
        macTriple.ComputeHash(targetBytes, 0, i)

        SummarizeMAC(macTriple, "MACTripleDES after computing the hash " + _
            "for the specified region of the byte array.")

        ' Create a new array with the number of valid bytes.
        Dim returnedArray(i) As Byte
        For j As Int16 = 0 To i - 1 Step 1

            returnedArray(j) = targetBytes(j)
        Next j

        Return returnedArray
    End Function
    Private Sub EncodeStream()
        Dim keyData(23) As Byte
        RandomNumberGenerator.Create().GetBytes(keyData)
        Dim macTriple As New MACTripleDES(keyData)
        Dim filePath As String
        filePath = System.IO.Directory.GetCurrentDirectory() + "\members.txt"
        Try
            Dim fileStream As New FileStream( _
                filePath, _
                FileMode.Open, _
                FileAccess.Read)

            macTriple.ComputeHash(fileStream)

            SummarizeMAC(macTriple, _
                "MACTripleDES after encoding a file stream.")
        Catch ex As Exception

            WriteLine("Specified path was not found: " + filePath)
        End Try
    End Sub
    Private Sub SummarizeMAC( _
        ByVal macTriple As MACTripleDES, _
        ByVal description As String)
        Dim classDescription As String = macTriple.ToString()

        Dim computedHash() As Byte = macTriple.Hash

        Dim hashSize As Integer = macTriple.HashSize

        Dim outputBlockSize As Integer = macTriple.OutputBlockSize

        ' Retrieve the key used in the hash algorithm.
        Dim key() As Byte = macTriple.Key

        WriteLine(vbCrLf + "**********************************")
        WriteLine(classDescription)
        WriteLine(description)
        WriteLine("----------------------------------")
        WriteLine("The size of the computed hash : " + hashSize.ToString())
        WriteLine("The key used in the hash algorithm : " + _
            Encoding.ASCII.GetString(key))
        WriteLine("The value of the computed hash : " + _
            Encoding.ASCII.GetString(computedHash))
    End Sub
    ' Write the specified message and carriage return to the output textbox.
    Private Sub WriteLine(ByVal message As String)
        tbxOutput.AppendText(message + vbCrLf)
    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 = "MACTripleDES"
        Me.Panel2.ResumeLayout(False)
        Me.Panel1.ResumeLayout(False)
        Me.ResumeLayout(False)

    End Sub

#End Region
End Class

import System.*;
import System.IO.*;
import System.Text.*;
import System.Collections.*;
import System.Security.Cryptography.*;

class Class1
{
    /** @attribute STAThread()
     */
    public static void main(String[] args)
    {
        EncodeNothing();
        EncodeMessage();
        EncodeStream();
        Console.WriteLine("This sample completed successfully; " 
            + "press Enter to exit.");
        Console.ReadLine();
    } //main

    // Compute the hash for an empty array; summarize the properties.
    private static void EncodeNothing()
    {
        MACTripleDES macTriple = new MACTripleDES();

        macTriple.Initialize();

        ubyte key[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(key);
        macTriple.set_Key(key);
        macTriple.ComputeHash(new ubyte[1024]);
        SummarizeMAC(macTriple, "MACTripleDES after initialization.");
    } //EncodeNothing

    // Compute the hash for a MACTripleDES that has transformed a
    // file stream.
    private static void EncodeStream()
    {
        ubyte keyData[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(keyData);
        MACTripleDES macTriple = new MACTripleDES(keyData);

        String filePath = System.IO.Directory.GetCurrentDirectory() 
            + "\\members.txt";
        try {
            FileStream fileStream = new FileStream(filePath, FileMode.Open, 
                FileAccess.Read);
            macTriple.ComputeHash(fileStream);
            SummarizeMAC(macTriple, 
                "MACTripleDES after encoding a file stream.");
        }
        catch (FileNotFoundException ex) {
            Console.WriteLine("Specified path was not found: " + filePath);
        }
    } //EncodeStream

    // Compute the hash for a MACTripleDES that has transformed a
    // byte array.
    private static void EncodeMessage()
    {
        ubyte keyData[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(keyData);
        MACTripleDES macTriple = new MACTripleDES(keyData);
        String message = "Encoding is fun!";
        ubyte encodedMessage[] = EncodeBytes(Encoding.get_ASCII().
            GetBytes(message));
        macTriple.ComputeHash(encodedMessage);
        SummarizeMAC(macTriple, "MACTripleDES after encoding a message.");
    } //EncodeMessage

    // Transform the byte array using MacTripleDES,
    // and then summarize its properties.
    private static ubyte[] EncodeBytes(ubyte sourceBytes[])
    {
        int currentPosition = 0;
        ubyte targetBytes[] = new ubyte[1024];
        int sourceByteLength = sourceBytes.get_Length();
        // Create an encryptor with a random key and the TripleDES
        // class name.
        ubyte key[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(key);
        String tripleDesName = "System.Security.Cryptography.TripleDES";
        MACTripleDES macTriple = new MACTripleDES(tripleDesName, key);

        // Retrieve the block size to read the bytes.
        int inputBlockSize = macTriple.get_InputBlockSize();
        try {
            // Determine if multiple blocks can be transformed.
            if (macTriple.get_CanTransformMultipleBlocks()) {
                int numBytesRead = 0;
                while (sourceByteLength - currentPosition >= inputBlockSize) {
                    // Transform the bytes from the currentposition in the
                    // sourceBytes array, writing the bytes to the 
                    // targetBytes array.
                    numBytesRead = macTriple.TransformBlock(sourceBytes, 
                        currentPosition, inputBlockSize, targetBytes, 
                        currentPosition);
                    // Advance the current position in the
                    // sourceBytes array.
                    currentPosition += numBytesRead;
                }
                // Transform the final block of bytes.
                ubyte finalBytes[] = macTriple.TransformFinalBlock(sourceBytes, 
                    currentPosition, sourceByteLength - currentPosition);
                // Copy the contents of the finalBytes array to the
                // targetBytes array.
                finalBytes.CopyTo(targetBytes, currentPosition);
            }
        }
        catch (System.Exception ex) {
            Console.WriteLine("Caught unexpected exception:" + ex.ToString());
        }
        // Determine if the current transform can be reused.
        if (!(macTriple.get_CanReuseTransform())) {
            // Free up any used resources.
            macTriple.Clear();
        }
        // Find the length of valid bytes (those without zeros).
        IEnumerator enum1 = targetBytes.GetEnumerator();
        int i = 0;
        while (enum1.MoveNext()) {
            if (enum1.get_Current().ToString().Equals("0")) {
                break;
            }
            i++;
        }
        // Compute the hash based on the valid bytes in the array.
        macTriple.ComputeHash(targetBytes, 0, i);

        SummarizeMAC(macTriple, "MACTripleDES after computing the hash " 
            + "for the specified region of the byte array.");
        // Create a new array with the number of valid bytes.
        ubyte returnedArray[] = new ubyte[i];
        for (int j = 0; j < i; j++) {
            returnedArray.set_Item(j, targetBytes.get_Item(j));
        }
        return returnedArray;
    } //EncodeBytes

    // Write a summary of the specified MACTripleDES to the console.
    private static void SummarizeMAC(MACTripleDES macTriple, 
        String description)
    {
        String classDescription = macTriple.ToString();

        ubyte computedHash[] = macTriple.get_Hash();

        int hashSize = macTriple.get_HashSize();

        int outputBlockSize = macTriple.get_OutputBlockSize();

        // Retrieve the key used in the hash algorithm.
        ubyte key[] = macTriple.get_Key();

        Console.WriteLine("\n**********************************");
        Console.WriteLine(classDescription);
        Console.WriteLine(description);
        Console.WriteLine("----------------------------------");
        Console.WriteLine("The size of the computed hash : " + hashSize);
        Console.WriteLine("The key used in the hash algorithm : " 
            + Encoding.get_ASCII().GetString(key));
        Console.WriteLine("The value of the computed hash : " 
            + Encoding.get_ASCII().GetString(computedHash));
    } //SummarizeMAC
} //Class1

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 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0
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