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KeyedHashAlgorithm Class

Represents the abstract class from which all implementations of keyed hash algorithms must derive.

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

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

/** @attribute ComVisibleAttribute(true) */ 
public abstract class KeyedHashAlgorithm extends HashAlgorithm
ComVisibleAttribute(true) 
public abstract class KeyedHashAlgorithm extends HashAlgorithm
Not applicable.

Hash functions map binary strings of an arbitrary length to small binary strings of a fixed length. A cryptographic hash function has the property that it is computationally infeasible to find two distinct inputs that hash to the same value. Small changes to the data result in large, unpredictable changes in the hash.

A keyed hash algorithm is a key-dependent, one-way hash function used as a message authentication code. Only someone who knows the key can verify the hash. Keyed hash algorithms provide authenticity without secrecy.

Hash functions are commonly used with digital signatures and for data integrity. The HMACSHA1 class is an example of a keyed hash algorithm.

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

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

Namespace Contoso
    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 = ""

            EncodeMessage()
            EncodeStream()

            ' Reset the cursor and conclude application.
            tbxOutput.AppendText(vbCrLf + "This sample completed " + _
                "successfully; press Exit to continue.")
            tbxOutput.Cursor = Cursors.Default
        End Sub

        ' Compute the hash for a ContosoKeyedHash that has transformed
        ' a file stream.
        Private Sub EncodeStream()
            Dim keyData(24) As Byte
            RandomNumberGenerator.Create.GetBytes(keyData)
            Dim localCrypto As New ContosoKeyedHash(keyData)

            Dim filePath As String
            filePath = System.IO.Directory.GetCurrentDirectory() + _
                "\members.txt"

            Try
                Dim fileStream As _
                    New FileStream(filePath, FileMode.Open, FileAccess.Read)

                localCrypto.ComputeHash(fileStream)

                SummarizeMAC(localCrypto, _
                    "ContosoKeyedHash after encoding a file stream.")
            Catch ex As FileNotFoundException
                WriteLine("Specified path was not found: " + filePath)
            End Try

        End Sub

        ' Compute the hash for a ContosoKeyedHash that has transformed
        ' a byte array.
        Private Sub EncodeMessage()

            Dim keyData(24) As Byte
            RandomNumberGenerator.Create().GetBytes(keyData)
            Dim localCrypto As New ContosoKeyedHash(keyData)

            Dim message As String = "Hello World."
            Dim encodedMessage() As Byte = _
                EncodeBytes(Encoding.ASCII.GetBytes(message))

            localCrypto.ComputeHash(encodedMessage)

            SummarizeMAC(localCrypto, _
                "ContosoKeyedHash after encoding a message.")
        End Sub

        ' Transform the byte array using ContosoKeyedHash,
        ' then summarize its properties.
        Private Function EncodeBytes(ByVal sourceBytes As Byte()) As Byte()
            Dim currentPosition As Int16 = 0
            Dim targetBytes(1024) As Byte
            Dim sourceByteLength As Int16 = sourceBytes.Length

            ' Create an encryptor with a random key and the KeyedHashAlgorithm
            ' class name.
            Dim key(24) As Byte
            RandomNumberGenerator.Create().GetBytes(key)
            Dim keyedHashName As String 
            keyedHashName = "System.Security.Cryptography.KeyedHashAlgorithm"
            Dim localCrypto As New ContosoKeyedHash(keyedHashName, key)

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

            Try
                ' Determine if multiple blocks can be transformed.
                If (localCrypto.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 = localCrypto.TransformBlock( _
                            sourceBytes, _
                            currentPosition, _
                            inputBlockSize, _
                            targetBytes, _
                            currentPosition)

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

                    ' Transform the final block of bytes.
                    Dim finalBytes() As Byte
                    finalBytes = localCrypto.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

            ' Find the length of valid bytes (those without zeros).
            Dim enum1 As IEnumerator = targetBytes.GetEnumerator()
            Dim i As Int16

            While (enum1.MoveNext())
                If (enum1.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.
            'Dim somebytes() As Byte
            'somebytes = localCrypto.ComputeHash(targetBytes, 0, i)
            localCrypto.ComputeHash(targetBytes, 0, i)

            SummarizeMAC(localCrypto, "ContosoKeyedHash after computing " + _
                "hash for specified region of byte array")

            ' Determine if the current transform can be reused.
            If (Not localCrypto.CanReuseTransform) Then

                ' Free up any used resources.
                localCrypto.Clear()

                localCrypto.Initialize()
            End If

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

            Return returnedArray
        End Function
        ' Write a summary of the specified ContosoKeyedHash to the 
        ' console window.
        Private Sub SummarizeMAC( _
            ByVal localCrypto As ContosoKeyedHash, _
            ByVal description As String)

            Dim classDescription As String = localCrypto.ToString()

            Dim computedHash() As Byte = localCrypto.Hash

            Dim hashSize As Integer = localCrypto.HashSize

            Dim outputBlockSize As Integer = localCrypto.OutputBlockSize

            ' Retrieve the key used in the hash algorithm.
            Dim key() As Byte = localCrypto.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
        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 = "KeyedHashAlgorithm"
            Me.Panel2.ResumeLayout(False)
            Me.Panel1.ResumeLayout(False)
            Me.ResumeLayout(False)
        End Sub
#End Region
    End Class
End Namespace

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

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

    // Compute the hash for a ContosoKeyedHash that has transformed a
    // file stream.
    private static void EncodeStream()
    {
        ubyte keyData[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(keyData);
        ContosoKeyedHash localCrypto = new ContosoKeyedHash(keyData);
        String filePath = System.IO.Directory.GetCurrentDirectory() 
            + "\\members.txt";
        try {
            FileStream fileStream = new FileStream(filePath, FileMode.Open, 
                FileAccess.Read);
            localCrypto.ComputeHash(fileStream);
            SummarizeMAC(localCrypto, 
                "ContosoKeyedHash after encoding a file stream.");
        }
        catch (FileNotFoundException exp) {
            Console.WriteLine("The specified path was not found: " + filePath);
        }
    } //EncodeStream

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

    // Transform the byte array using ContosoKeyedHash,
    // 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
        // KeyedHashAlgorithm class name.
        ubyte key[] = new ubyte[24];
        RandomNumberGenerator.Create().GetBytes(key);
        String keyedHashName = "System.Security.Cryptography.KeyedHashAlgorithm";
        ContosoKeyedHash localCrypto = new ContosoKeyedHash(keyedHashName, key);
        // Retrieve the block size to read the bytes.
        int inputBlockSize = localCrypto.get_InputBlockSize();
        try {
            // Determine if multiple blocks can be transformed.
            if (localCrypto.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 = localCrypto.TransformBlock(sourceBytes, 
                        currentPosition, inputBlockSize, targetBytes, 
                        currentPosition);
                    // Advance the current position in the source array.
                    currentPosition += numBytesRead;
                }
                
                // Transform the final block of bytes.
                ubyte finalBytes[] = localCrypto.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());
        }
        // 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.
        localCrypto.ComputeHash(targetBytes, 0, i);

        SummarizeMAC(localCrypto, "ContosoKeyedHash after computing " 
            + "hash for specified region of byte array");
        
        // Determine if the current transform can be reused.
        if (!(localCrypto.get_CanReuseTransform())) {
            // Free up any used resources.
            localCrypto.Clear();

            localCrypto.Initialize();
        }
        // 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 ContosoKeyedHash to the
    // console window.
    private static void SummarizeMAC(ContosoKeyedHash localCrypto, 
        String description)
    {
        String classDescription = localCrypto.ToString();

        ubyte computedHash[] = localCrypto.get_Hash();

        int hashSize = localCrypto.get_HashSize();

        int outputBlockSize = localCrypto.get_OutputBlockSize();

        // Retrieve the key used in the hash algorithm.
        ubyte key[] = localCrypto.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
} //EncodeWithContoso

Imports System
Imports System.Security.Cryptography

Namespace Contoso
    Public Class ContosoKeyedHash
        Inherits KeyedHashAlgorithm

        Dim keyedCrypto As KeyedHashAlgorithm

        Public Sub New(ByVal rgbKey() As Byte)
            Me.New("System.Security.Cryptography.KeyedHashAlgorithm", rgbKey)
        End Sub

        Public Sub New(ByVal keyedHashName As String, ByVal rgbKey() As Byte)
            ' Make sure we know which algorithm to use
            If (Not rgbKey Is Nothing) Then
                KeyValue = rgbKey
                HashSizeValue = 160

                ' Create a KeyedHashAlgorithm encryptor
                If (keyedHashName Is Nothing) Then
                    keyedCrypto = KeyedHashAlgorithm.Create()
                Else
                    keyedCrypto = KeyedHashAlgorithm.Create(keyedHashName)
                End If

                '                keyedCrypto.Key = rgbKey
            Else
                Throw New ArgumentNullException("rgbKey")
            End If
        End Sub

        ' Override abstract methods from the HashAlgorithm class.
        Public Overrides Sub Initialize()

        End Sub

        ' Override the Key property to use the local key from keyedCrypto.
        Public Overrides Property Key() As Byte()
            Get
                Return CType(keyedCrypto.Key.Clone(), Byte())
            End Get
            Set(ByVal Value As Byte())
                keyedCrypto.Key = CType(Value.Clone(), Byte())
            End Set
        End Property

        Protected Overrides Sub HashCore( _
            ByVal rgbData() As Byte, _
            ByVal ibStart As Integer, _
            ByVal cbSize As Integer)

        End Sub
        Protected Overrides Function HashFinal() As Byte()
            Dim returnBytes(0) As Byte
            Return returnBytes
        End Function
    End Class
End Namespace


import System.*;
import System.Security.Cryptography.*;

class ContosoKeyedHash extends KeyedHashAlgorithm
{
    private KeyedHashAlgorithm keyedCrypto;

    public ContosoKeyedHash(ubyte rgbKey[])
    {
        this("System.Security.Cryptography.KeyedHashAlgorithm", rgbKey);
    } //ContosoKeyedHash

    public ContosoKeyedHash(String keyedHashName, ubyte rgbKey[])
    {
        // Make sure we know which algorithm to use
        if (rgbKey != null) {
            KeyValue = rgbKey;
            HashSizeValue = 160;
            // Create a KeyedHashAlgorithm encryptor
            if (keyedHashName == null) {
                keyedCrypto = KeyedHashAlgorithm.Create();
            }
            else {
                keyedCrypto = KeyedHashAlgorithm.Create(keyedHashName);
            }
        } 
        else {
            throw new ArgumentNullException("rgbKey");
        }
    } //ContosoKeyedHash

    // Override abstract methods from the HashAlgorithm class.
    public void Initialize()
    {
    } //Initialize 

    /** @property 
     */
    public ubyte[] get_Key()
    {
        return (ubyte[])keyedCrypto.get_Key().Clone();
    } //get_Key

    /** @property 
     */
    public void set_Key(ubyte value[])
    {
        keyedCrypto.set_Key((ubyte[])(value.Clone()));
    } //set_Key

    protected void HashCore(ubyte rgbData[], int ibStart, int cbSize)
    {
    } //HashCore

    protected ubyte[] HashFinal()
    {
        return new ubyte[0];
    } //HashFinal
} //ContosoKeyedHash

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 Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0
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