KeyedHashAlgorithm KeyedHashAlgorithm KeyedHashAlgorithm KeyedHashAlgorithm Class

Definition

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

public ref class KeyedHashAlgorithm abstract : System::Security::Cryptography::HashAlgorithm
[System.Runtime.InteropServices.ComVisible(true)]
public abstract class KeyedHashAlgorithm : System.Security.Cryptography.HashAlgorithm
type KeyedHashAlgorithm = class
    inherit HashAlgorithm
Public MustInherit Class KeyedHashAlgorithm
Inherits HashAlgorithm
Inheritance
KeyedHashAlgorithmKeyedHashAlgorithmKeyedHashAlgorithmKeyedHashAlgorithm
Derived
Attributes

Examples

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

using System;
using System.Security.Cryptography;

public class TestHMACMD5
{
    static private void PrintByteArray(Byte[] arr)
    {
        int i;
        Console.WriteLine("Length: " + arr.Length);
        for (i = 0; i < arr.Length; i++)
        {
            Console.Write("{0:X}", arr[i]);
            Console.Write("    ");
            if ((i + 9) % 8 == 0) Console.WriteLine();
        }
        if (i % 8 != 0) Console.WriteLine();
    }
    public static void Main()
    {
        // Create a key.
        byte[] key1 = { 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b };
        // Pass the key to the constructor of the HMACMD5 class.  
        HMACMD5 hmac1 = new HMACMD5(key1);

        // Create another key.
        byte[] key2 = System.Text.Encoding.ASCII.GetBytes("KeyString");
        // Pass the key to the constructor of the HMACMD5 class.  
        HMACMD5 hmac2 = new HMACMD5(key2);

        // Encode a string into a byte array, create a hash of the array,
        // and print the hash to the screen.
        byte[] data1 = System.Text.Encoding.ASCII.GetBytes("Hi There");
        PrintByteArray(hmac1.ComputeHash(data1));

        // Encode a string into a byte array, create a hash of the array,
        // and print the hash to the screen.
        byte[] data2 = System.Text.Encoding.ASCII.GetBytes("This data will be hashed.");
        PrintByteArray(hmac2.ComputeHash(data2));
    }
}
public class HMACMD5 : KeyedHashAlgorithm
{
    private MD5 hash1;
    private MD5 hash2;
    private bool bHashing = false;

    private byte[] rgbInner = new byte[64];
    private byte[] rgbOuter = new byte[64];

    public HMACMD5(byte[] rgbKey)
    {
        HashSizeValue = 128;
        // Create the hash algorithms.
        hash1 = MD5.Create();
        hash2 = MD5.Create();
        // Get the key.
        if (rgbKey.Length > 64)
        {
            KeyValue = hash1.ComputeHash(rgbKey);
            // No need to call Initialize; ComputeHash does it automatically.
        }
        else
        {
            KeyValue = (byte[])rgbKey.Clone();
        }
        // Compute rgbInner and rgbOuter.
        int i = 0;
        for (i = 0; i < 64; i++)
        {
            rgbInner[i] = 0x36;
            rgbOuter[i] = 0x5C;
        }
        for (i = 0; i < KeyValue.Length; i++)
        {
            rgbInner[i] ^= KeyValue[i];
            rgbOuter[i] ^= KeyValue[i];
        }
    }

    public override byte[] Key
    {
        get { return (byte[])KeyValue.Clone(); }
        set
        {
            if (bHashing)
            {
                throw new Exception("Cannot change key during hash operation");
            }
            if (value.Length > 64)
            {
                KeyValue = hash1.ComputeHash(value);
                // No need to call Initialize; ComputeHash does it automatically.
            }
            else
            {
                KeyValue = (byte[])value.Clone();
            }
            // Compute rgbInner and rgbOuter.
            int i = 0;
            for (i = 0; i < 64; i++)
            {
                rgbInner[i] = 0x36;
                rgbOuter[i] = 0x5C;
            }
            for (i = 0; i < KeyValue.Length; i++)
            {
                rgbInner[i] ^= KeyValue[i];
                rgbOuter[i] ^= KeyValue[i];
            }
        }
    }
    public override void Initialize()
    {
        hash1.Initialize();
        hash2.Initialize();
        bHashing = false;
    }
    protected override void HashCore(byte[] rgb, int ib, int cb)
    {
        if (bHashing == false)
        {
            hash1.TransformBlock(rgbInner, 0, 64, rgbInner, 0);
            bHashing = true;
        }
        hash1.TransformBlock(rgb, ib, cb, rgb, ib);
    }

    protected override byte[] HashFinal()
    {
        if (bHashing == false)
        {
            hash1.TransformBlock(rgbInner, 0, 64, rgbInner, 0);
            bHashing = true;
        }
        // Finalize the original hash.
        hash1.TransformFinalBlock(new byte[0], 0, 0);
        // Write the outer array.
        hash2.TransformBlock(rgbOuter, 0, 64, rgbOuter, 0);
        // Write the inner hash and finalize the hash.
        hash2.TransformFinalBlock(hash1.Hash, 0, hash1.Hash.Length);
        bHashing = false;
        return hash2.Hash;
    }
}
Imports System
Imports System.Security.Cryptography
 _

Public Class TestHMACMD5

    Private Shared Sub PrintByteArray(ByVal arr() As [Byte])
        Dim i As Integer
        Console.WriteLine(("Length: " + arr.Length.ToString()))
        For i = 0 To arr.Length - 1
            Console.Write("{0:X}", arr(i))
            Console.Write("    ")
            If (i + 9) Mod 8 = 0 Then
                Console.WriteLine()
            End If
        Next i
        If i Mod 8 <> 0 Then
            Console.WriteLine()
        End If
    End Sub

    Public Shared Sub Main()
        ' Create a key.
        Dim key1 As Byte() = {&HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB, &HB}
        ' Pass the key to the constructor of the HMACMD5 class.  
        Dim hmac1 As New HMACMD5(key1)

        ' Create another key.
        Dim key2 As Byte() = System.Text.Encoding.ASCII.GetBytes("KeyString")
        ' Pass the key to the constructor of the HMACMD5 class.  
        Dim hmac2 As New HMACMD5(key2)

        ' Encode a string into a byte array, create a hash of the array,
        ' and print the hash to the screen.
        Dim data1 As Byte() = System.Text.Encoding.ASCII.GetBytes("Hi There")
        PrintByteArray(hmac1.ComputeHash(data1))

        ' Encode a string into a byte array, create a hash of the array,
        ' and print the hash to the screen.
        Dim data2 As Byte() = System.Text.Encoding.ASCII.GetBytes("This data will be hashed.")
        PrintByteArray(hmac2.ComputeHash(data2))
    End Sub
End Class
 _

Public Class HMACMD5
    Inherits KeyedHashAlgorithm
    Private hash1 As MD5
    Private hash2 As MD5
    Private bHashing As Boolean = False

    Private rgbInner(64) As Byte
    Private rgbOuter(64) As Byte


    Public Sub New(ByVal rgbKey() As Byte)
        HashSizeValue = 128
        ' Create the hash algorithms.
        hash1 = MD5.Create()
        hash2 = MD5.Create()
        ' Get the key.
        If rgbKey.Length > 64 Then
            KeyValue = hash1.ComputeHash(rgbKey)
            ' No need to call Initialize; ComputeHash does it automatically.
        Else
            KeyValue = CType(rgbKey.Clone(), Byte())
        End If
        ' Compute rgbInner and rgbOuter.
        Dim i As Integer = 0
        For i = 0 To 63
            rgbInner(i) = &H36
            rgbOuter(i) = &H5C
        Next i
        i = 0
        For i = 0 To KeyValue.Length - 1
            rgbInner(i) = rgbInner(i) Xor KeyValue(i)
            rgbOuter(i) = rgbOuter(i) Xor KeyValue(i)
        Next i
    End Sub


    Public Overrides Property Key() As Byte()
        Get
            Return CType(KeyValue.Clone(), Byte())
        End Get
        Set(ByVal Value As Byte())
            If bHashing Then
                Throw New Exception("Cannot change key during hash operation")
            End If
            If value.Length > 64 Then
                KeyValue = hash1.ComputeHash(value)
                ' No need to call Initialize; ComputeHash does it automatically.
            Else
                KeyValue = CType(value.Clone(), Byte())
            End If
            ' Compute rgbInner and rgbOuter.
            Dim i As Integer = 0
            For i = 0 To 63
                rgbInner(i) = &H36
                rgbOuter(i) = &H5C
            Next i
            For i = 0 To KeyValue.Length - 1
                rgbInner(i) ^= KeyValue(i)
                rgbOuter(i) ^= KeyValue(i)
            Next i
        End Set
    End Property


    Public Overrides Sub Initialize()
        hash1.Initialize()
        hash2.Initialize()
        bHashing = False
    End Sub


    Protected Overrides Sub HashCore(ByVal rgb() As Byte, ByVal ib As Integer, ByVal cb As Integer)
        If bHashing = False Then
            hash1.TransformBlock(rgbInner, 0, 64, rgbInner, 0)
            bHashing = True
        End If
        hash1.TransformBlock(rgb, ib, cb, rgb, ib)
    End Sub


    Protected Overrides Function HashFinal() As Byte()
        If bHashing = False Then
            hash1.TransformBlock(rgbInner, 0, 64, rgbInner, 0)
            bHashing = True
        End If
        ' Finalize the original hash.
        hash1.TransformFinalBlock(New Byte(0) {}, 0, 0)
        ' Write the outer array.
        hash2.TransformBlock(rgbOuter, 0, 64, rgbOuter, 0)
        ' Write the inner hash and finalize the hash.
        hash2.TransformFinalBlock(hash1.Hash, 0, hash1.Hash.Length)
        bHashing = False
        Return hash2.Hash
    End Function
End Class

Remarks

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.

Constructors

KeyedHashAlgorithm() KeyedHashAlgorithm() KeyedHashAlgorithm() KeyedHashAlgorithm()

Initializes a new instance of the KeyedHashAlgorithm class.

Fields

HashSizeValue HashSizeValue HashSizeValue HashSizeValue

Represents the size, in bits, of the computed hash code.

(Inherited from HashAlgorithm)
HashValue HashValue HashValue HashValue

Represents the value of the computed hash code.

(Inherited from HashAlgorithm)
KeyValue KeyValue KeyValue KeyValue

The key to use in the hash algorithm.

State State State State

Represents the state of the hash computation.

(Inherited from HashAlgorithm)

Properties

CanReuseTransform CanReuseTransform CanReuseTransform CanReuseTransform

Gets a value indicating whether the current transform can be reused.

(Inherited from HashAlgorithm)
CanTransformMultipleBlocks CanTransformMultipleBlocks CanTransformMultipleBlocks CanTransformMultipleBlocks

When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.

(Inherited from HashAlgorithm)
Hash Hash Hash Hash

Gets the value of the computed hash code.

(Inherited from HashAlgorithm)
HashSize HashSize HashSize HashSize

Gets the size, in bits, of the computed hash code.

(Inherited from HashAlgorithm)
InputBlockSize InputBlockSize InputBlockSize InputBlockSize

When overridden in a derived class, gets the input block size.

(Inherited from HashAlgorithm)
Key Key Key Key

Gets or sets the key to use in the hash algorithm.

OutputBlockSize OutputBlockSize OutputBlockSize OutputBlockSize

When overridden in a derived class, gets the output block size.

(Inherited from HashAlgorithm)

Methods

Clear() Clear() Clear() Clear()

Releases all resources used by the HashAlgorithm class.

(Inherited from HashAlgorithm)
ComputeHash(Byte[]) ComputeHash(Byte[]) ComputeHash(Byte[]) ComputeHash(Byte[])

Computes the hash value for the specified byte array.

(Inherited from HashAlgorithm)
ComputeHash(Byte[], Int32, Int32) ComputeHash(Byte[], Int32, Int32) ComputeHash(Byte[], Int32, Int32) ComputeHash(Byte[], Int32, Int32)

Computes the hash value for the specified region of the specified byte array.

(Inherited from HashAlgorithm)
ComputeHash(Stream) ComputeHash(Stream) ComputeHash(Stream) ComputeHash(Stream)

Computes the hash value for the specified Stream object.

(Inherited from HashAlgorithm)
Create() Create() Create() Create()

Creates an instance of the default implementation of a keyed hash algorithm.

Create(String) Create(String) Create(String) Create(String)

Creates an instance of the specified implementation of a keyed hash algorithm.

Dispose() Dispose() Dispose() Dispose()

Releases all resources used by the current instance of the HashAlgorithm class.

(Inherited from HashAlgorithm)
Dispose(Boolean) Dispose(Boolean) Dispose(Boolean) Dispose(Boolean)

Releases the unmanaged resources used by the KeyedHashAlgorithm and optionally releases the managed resources.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
Finalize() Finalize() Finalize() Finalize()
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serves as the default hash function.

(Inherited from Object)
GetType() GetType() GetType() GetType()

Gets the Type of the current instance.

(Inherited from Object)
HashCore(Byte[], Int32, Int32) HashCore(Byte[], Int32, Int32) HashCore(Byte[], Int32, Int32) HashCore(Byte[], Int32, Int32)

When overridden in a derived class, routes data written to the object into the hash algorithm for computing the hash.

(Inherited from HashAlgorithm)
HashCore(ReadOnlySpan<Byte>) HashCore(ReadOnlySpan<Byte>) HashCore(ReadOnlySpan<Byte>) HashCore(ReadOnlySpan<Byte>) Inherited from HashAlgorithm
HashFinal() HashFinal() HashFinal() HashFinal()

When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object.

(Inherited from HashAlgorithm)
Initialize() Initialize() Initialize() Initialize()

Initializes an implementation of the HashAlgorithm class.

(Inherited from HashAlgorithm)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
ToString() ToString() ToString() ToString()

Returns a string that represents the current object.

(Inherited from Object)
TransformBlock(Byte[], Int32, Int32, Byte[], Int32) TransformBlock(Byte[], Int32, Int32, Byte[], Int32) TransformBlock(Byte[], Int32, Int32, Byte[], Int32) TransformBlock(Byte[], Int32, Int32, Byte[], Int32)

Computes the hash value for the specified region of the input byte array and copies the specified region of the input byte array to the specified region of the output byte array.

(Inherited from HashAlgorithm)
TransformFinalBlock(Byte[], Int32, Int32) TransformFinalBlock(Byte[], Int32, Int32) TransformFinalBlock(Byte[], Int32, Int32) TransformFinalBlock(Byte[], Int32, Int32)

Computes the hash value for the specified region of the specified byte array.

(Inherited from HashAlgorithm)
TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) Inherited from HashAlgorithm
TryHashFinal(Span<Byte>, Int32) TryHashFinal(Span<Byte>, Int32) TryHashFinal(Span<Byte>, Int32) TryHashFinal(Span<Byte>, Int32) Inherited from HashAlgorithm

Explicit Interface Implementations

IDisposable.Dispose() IDisposable.Dispose() IDisposable.Dispose() IDisposable.Dispose() Inherited from HashAlgorithm

Applies to