KeyedHashAlgorithm Class
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Represents the abstract class from which all implementations of keyed hash algorithms must derive.
public ref class KeyedHashAlgorithm abstract : System::Security::Cryptography::HashAlgorithm
public abstract class KeyedHashAlgorithm : System.Security.Cryptography.HashAlgorithm
[System.Runtime.InteropServices.ComVisible(true)]
public abstract class KeyedHashAlgorithm : System.Security.Cryptography.HashAlgorithm
type KeyedHashAlgorithm = class
inherit HashAlgorithm
[<System.Runtime.InteropServices.ComVisible(true)>]
type KeyedHashAlgorithm = class
inherit HashAlgorithm
Public MustInherit Class KeyedHashAlgorithm
Inherits HashAlgorithm
- Inheritance
- 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.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.
Due to collision problems with SHA1, Microsoft recommends a security model based on SHA256 or better.
Constructors
KeyedHashAlgorithm() |
Initializes a new instance of the KeyedHashAlgorithm class. |
Fields
HashSizeValue |
Represents the size, in bits, of the computed hash code. (Inherited from HashAlgorithm) |
HashValue |
Represents the value of the computed hash code. (Inherited from HashAlgorithm) |
KeyValue |
The key to use in the hash algorithm. |
State |
Represents the state of the hash computation. (Inherited from HashAlgorithm) |
Properties
CanReuseTransform |
Gets a value indicating whether the current transform can be reused. (Inherited from HashAlgorithm) |
CanTransformMultipleBlocks |
When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed. (Inherited from HashAlgorithm) |
Hash |
Gets the value of the computed hash code. (Inherited from HashAlgorithm) |
HashSize |
Gets the size, in bits, of the computed hash code. (Inherited from HashAlgorithm) |
InputBlockSize |
When overridden in a derived class, gets the input block size. (Inherited from HashAlgorithm) |
Key |
Gets or sets the key to use in the hash algorithm. |
OutputBlockSize |
When overridden in a derived class, gets the output block size. (Inherited from HashAlgorithm) |
Methods
Clear() |
Releases all resources used by the HashAlgorithm class. (Inherited from HashAlgorithm) |
ComputeHash(Byte[]) |
Computes the hash value for the specified byte array. (Inherited from HashAlgorithm) |
ComputeHash(Byte[], Int32, Int32) |
Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm) |
ComputeHash(Stream) |
Computes the hash value for the specified Stream object. (Inherited from HashAlgorithm) |
ComputeHashAsync(Stream, CancellationToken) |
Asynchronously computes the hash value for the specified Stream object. (Inherited from HashAlgorithm) |
Create() |
Obsolete.
Obsolete.
Creates an instance of the default implementation of a keyed hash algorithm. |
Create(String) |
Obsolete.
Creates an instance of the specified implementation of a keyed hash algorithm. |
Dispose() |
Releases all resources used by the current instance of the HashAlgorithm class. (Inherited from HashAlgorithm) |
Dispose(Boolean) |
Releases the unmanaged resources used by the KeyedHashAlgorithm and optionally releases the managed resources. |
Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
Finalize() |
This member overrides Finalize(), and more complete documentation might be available in that topic. Allows an Object to attempt to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. |
GetHashCode() |
Serves as the default hash function. (Inherited from Object) |
GetType() |
Gets the Type of the current instance. (Inherited from Object) |
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>) |
Routes data written to the object into the hash algorithm for computing the hash. (Inherited from HashAlgorithm) |
HashFinal() |
When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic hash algorithm. (Inherited from HashAlgorithm) |
Initialize() |
Resets the hash algorithm to its initial state. (Inherited from HashAlgorithm) |
MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
ToString() |
Returns a string that represents the current object. (Inherited from Object) |
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) |
Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm) |
TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32) |
Attempts to compute the hash value for the specified byte array. (Inherited from HashAlgorithm) |
TryHashFinal(Span<Byte>, Int32) |
Attempts to finalize the hash computation after the last data is processed by the hash algorithm. (Inherited from HashAlgorithm) |
Explicit Interface Implementations
IDisposable.Dispose() |
Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources. (Inherited from HashAlgorithm) |