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Estendendo a classe KeyedHashAlgorithm

As classes de criptografia fornecidas pelo .NET estrutura são extremamente extensíveis.Esta seção fornece um exemplo de como estender essas classes de criptografia, criando uma classe de algoritmo de hash com chave que implementa o MD5 algoritmo de hash.

Um algoritmo de hash com chave é uma função de hash unidirecional, dependentes de chave usada sistema autônomo um código de autenticação de mensagem.O .NET estrutura fornece dois esse hash com chave algoritmo classes (HMACSHA1 e MACTripleDES), que derivam de resumo Classe KeyedHashAlgorithm.Se você deseja implementar uma classe de algoritmo de hash com chave que implementa um algoritmo de hash diferente do que aquelas fornecidas no .NET estrutura, você poderá criar uma nova classe derivada de KeyedHashAlgorithm que usa seu algoritmo de hash preferencial.

O exemplo a seguir cria uma nova classe de algoritmo de hash com chave usando o MD5 algoritmo de hash.Porque esta classe herda do KeyedHashAlgorithm classe, ele pode ser usado com com facilidade com outras classes de criptografia gerenciadas, como a CryptoStream classe.

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;
    }        
}

Este exemplo estende a KeyedHashAlgorithm classe para usar o MD5 algoritmo de hash em uma classe chamada HMACMD5. Quando executado, esse código cria duas instâncias do HMACMD5 classe, passando chaves diferentes para cada construtor. Em seguida, os valores das duas seqüências de caracteres de hashes e imprime o seguinte para o console.

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

Consulte também

Outros recursos

Tarefas de criptografia

Serviços de criptografia