Extender la clase KeyedHashAlgorithm
Actualización: noviembre 2007
Las clases criptográficas suministradas por .NET Framework son extremadamente extensibles. En esta sección se proporciona un ejemplo de cómo extender estas clases criptográficas creando una clase de algoritmos hash con clave que implemente el algoritmo hash MD5.
Un algoritmo hash con clave es una función hash unidireccional y dependiente de una clave utilizada como código de autenticación de un mensaje. .NET Framework proporciona dos clases de algoritmos hash con clave (HMACSHA1 y MACTripleDES), que se derivan de la clase KeyedHashAlgorithm abstracta. Si desea implementar una clase de algoritmos hash con clave que incluya un algoritmo hash distinto de los proporcionados por .NET Framework, podrá crear una nueva clase derivada de KeyedHashAlgorithm que use dicho algoritmo.
En el ejemplo siguiente se crea una nueva clase de algoritmos hash con clave que usa el algoritmo hash MD5. Como esta clase hereda de la clase KeyedHashAlgorithm, se puede usar fácilmente con otras clases de criptografía administradas como CryptoStream.
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
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;
}
}
En este ejemplo se extiende la clase KeyedHashAlgorithm para usar el algoritmo hash MD5 en una clase denominada HMACMD5. Una vez ejecutado, este código crea dos instancias de la clase HMACMD5, pasando claves distintas a cada constructor. A continuación, genera una clave hash para los dos valores e imprime lo siguiente en la consola.
Length: 16
92 94 72 7A 36 38 BB 1C
13 F4 8E F8 15 8B FC 9D
Length: 16
1 10 3A 9 C2 10 6E E1
1 13 9B 7D DA EA A3 EC