KeyedHashAlgorithm Class
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
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
System.Security.Cryptography.HashAlgorithm
System.Security.Cryptography.KeyedHashAlgorithm
System.Security.Cryptography.HMAC
System.Security.Cryptography.MACTripleDES
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.
Reference
KeyedHashAlgorithm MembersSystem.Security.Cryptography Namespace