HMACSHA256 Classe

Definição

Calcula um HMAC (Hash-based Message Authentication Code) usando a função de hash SHA256.Computes a Hash-based Message Authentication Code (HMAC) by using the SHA256 hash function.

public ref class HMACSHA256 : System::Security::Cryptography::HMAC
[System.Runtime.Versioning.UnsupportedOSPlatform("browser")]
public class HMACSHA256 : System.Security.Cryptography.HMAC
public class HMACSHA256 : System.Security.Cryptography.HMAC
[System.Runtime.InteropServices.ComVisible(true)]
public class HMACSHA256 : System.Security.Cryptography.HMAC
[<System.Runtime.Versioning.UnsupportedOSPlatform("browser")>]
type HMACSHA256 = class
    inherit HMAC
type HMACSHA256 = class
    inherit HMAC
[<System.Runtime.InteropServices.ComVisible(true)>]
type HMACSHA256 = class
    inherit HMAC
Public Class HMACSHA256
Inherits HMAC
Herança
Atributos

Exemplos

O exemplo a seguir mostra como assinar um arquivo usando o HMACSHA256 objeto e como verificar o arquivo.The following example shows how to sign a file by using the HMACSHA256 object and then how to verify the file.

using namespace System;
using namespace System::IO;
using namespace System::Security::Cryptography;

// Computes a keyed hash for a source file, creates a target file with the keyed hash
// prepended to the contents of the source file, then decodes the file and compares
// the source and the decoded files.
void EncodeFile( array<Byte>^key, String^ sourceFile, String^ destFile )
{
   
   // Initialize the keyed hash object.
   HMACSHA256^ myhmacsha256 = gcnew HMACSHA256( key );
   FileStream^ inStream = gcnew FileStream( sourceFile,FileMode::Open );
   FileStream^ outStream = gcnew FileStream( destFile,FileMode::Create );
   
   // Compute the hash of the input file.
   array<Byte>^hashValue = myhmacsha256->ComputeHash( inStream );
   
   // Reset inStream to the beginning of the file.
   inStream->Position = 0;
   
   // Write the computed hash value to the output file.
   outStream->Write( hashValue, 0, hashValue->Length );
   
   // Copy the contents of the sourceFile to the destFile.
   int bytesRead;
   
   // read 1K at a time
   array<Byte>^buffer = gcnew array<Byte>(1024);
   do
   {
      
      // Read from the wrapping CryptoStream.
      bytesRead = inStream->Read( buffer, 0, 1024 );
      outStream->Write( buffer, 0, bytesRead );
   }
   while ( bytesRead > 0 );

   myhmacsha256->Clear();
   
   // Close the streams
   inStream->Close();
   outStream->Close();
   return;
} // end EncodeFile



// Decode the encoded file and compare to original file.
bool DecodeFile( array<Byte>^key, String^ sourceFile )
{
   
   // Initialize the keyed hash object. 
   HMACSHA256^ hmacsha256 = gcnew HMACSHA256( key );
   
   // Create an array to hold the keyed hash value read from the file.
   array<Byte>^storedHash = gcnew array<Byte>(hmacsha256->HashSize / 8);
   
   // Create a FileStream for the source file.
   FileStream^ inStream = gcnew FileStream( sourceFile,FileMode::Open );
   
   // Read in the storedHash.
   inStream->Read( storedHash, 0, storedHash->Length );
   
   // Compute the hash of the remaining contents of the file.
   // The stream is properly positioned at the beginning of the content, 
   // immediately after the stored hash value.
   array<Byte>^computedHash = hmacsha256->ComputeHash( inStream );
   
   // compare the computed hash with the stored value
   bool err = false;
   for ( int i = 0; i < storedHash->Length; i++ )
   {
      if ( computedHash[ i ] != storedHash[ i ] )
      {
         err = true;
      }
   }
   if (err)
        {
            Console::WriteLine("Hash values differ! Encoded file has been tampered with!");
            return false;
        }
        else
        {
            Console::WriteLine("Hash values agree -- no tampering occurred.");
            return true;
        }

} //end DecodeFile


int main()
{
   array<String^>^Fileargs = Environment::GetCommandLineArgs();
   String^ usageText = "Usage: HMACSHA256 inputfile.txt encodedfile.hsh\nYou must specify the two file names. Only the first file must exist.\n";
   
   //If no file names are specified, write usage text.
   if ( Fileargs->Length < 3 )
   {
      Console::WriteLine( usageText );
   }
   else
   {
      try
      {
         
         // Create a random key using a random number generator. This would be the
         //  secret key shared by sender and receiver.
         array<Byte>^secretkey = gcnew array<Byte>(64);
         
         //RNGCryptoServiceProvider is an implementation of a random number generator.
         RNGCryptoServiceProvider^ rng = gcnew RNGCryptoServiceProvider;
         
         // The array is now filled with cryptographically strong random bytes.
         rng->GetBytes( secretkey );
         
         // Use the secret key to encode the message file.
         EncodeFile( secretkey, Fileargs[ 1 ], Fileargs[ 2 ] );
         
         // Take the encoded file and decode
         DecodeFile( secretkey, Fileargs[ 2 ] );
      }
      catch ( IOException^ e ) 
      {
         Console::WriteLine( "Error: File not found", e );
      }

   }
} //end main


using System;
using System.IO;
using System.Security.Cryptography;

public class HMACSHA256example
{

    public static void Main(string[] Fileargs)
    {
        string dataFile;
        string signedFile;
        //If no file names are specified, create them.
        if (Fileargs.Length < 2)
        {
            dataFile = @"text.txt";
            signedFile = "signedFile.enc";

            if (!File.Exists(dataFile))
            {
                // Create a file to write to.
                using (StreamWriter sw = File.CreateText(dataFile))
                {
                    sw.WriteLine("Here is a message to sign");
                }
            }
        }
        else
        {
            dataFile = Fileargs[0];
            signedFile = Fileargs[1];
        }
        try
        {
            // Create a random key using a random number generator. This would be the
            //  secret key shared by sender and receiver.
            byte[] secretkey = new Byte[64];
            //RNGCryptoServiceProvider is an implementation of a random number generator.
            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
            {
                // The array is now filled with cryptographically strong random bytes.
                rng.GetBytes(secretkey);

                // Use the secret key to sign the message file.
                SignFile(secretkey, dataFile, signedFile);

                // Verify the signed file
                VerifyFile(secretkey, signedFile);
            }
        }
        catch (IOException e)
        {
            Console.WriteLine("Error: File not found", e);
        }
    }  //end main
    // Computes a keyed hash for a source file and creates a target file with the keyed hash
    // prepended to the contents of the source file.
    public static void SignFile(byte[] key, String sourceFile, String destFile)
    {
        // Initialize the keyed hash object.
        using (HMACSHA256 hmac = new HMACSHA256(key))
        {
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
            {
                using (FileStream outStream = new FileStream(destFile, FileMode.Create))
                {
                    // Compute the hash of the input file.
                    byte[] hashValue = hmac.ComputeHash(inStream);
                    // Reset inStream to the beginning of the file.
                    inStream.Position = 0;
                    // Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length);
                    // Copy the contents of the sourceFile to the destFile.
                    int bytesRead;
                    // read 1K at a time
                    byte[] buffer = new byte[1024];
                    do
                    {
                        // Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024);
                        outStream.Write(buffer, 0, bytesRead);
                    } while (bytesRead > 0);
                }
            }
        }
        return;
    } // end SignFile

    // Compares the key in the source file with a new key created for the data portion of the file. If the keys
    // compare the data has not been tampered with.
    public static bool VerifyFile(byte[] key, String sourceFile)
    {
        bool err = false;
        // Initialize the keyed hash object.
        using (HMACSHA256 hmac = new HMACSHA256(key))
        {
            // Create an array to hold the keyed hash value read from the file.
            byte[] storedHash = new byte[hmac.HashSize / 8];
            // Create a FileStream for the source file.
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
            {
                // Read in the storedHash.
                inStream.Read(storedHash, 0, storedHash.Length);
                // Compute the hash of the remaining contents of the file.
                // The stream is properly positioned at the beginning of the content,
                // immediately after the stored hash value.
                byte[] computedHash = hmac.ComputeHash(inStream);
                // compare the computed hash with the stored value

                for (int i = 0; i < storedHash.Length; i++)
                {
                    if (computedHash[i] != storedHash[i])
                    {
                        err = true;
                    }
                }
            }
        }
        if (err)
        {
            Console.WriteLine("Hash values differ! Signed file has been tampered with!");
            return false;
        }
        else
        {
            Console.WriteLine("Hash values agree -- no tampering occurred.");
            return true;
        }
    } //end VerifyFile
} //end class
Imports System.IO
Imports System.Security.Cryptography

Public Class HMACSHA256example

    Public Shared Sub Main(ByVal Fileargs() As String)
        Dim dataFile As String
        Dim signedFile As String
        'If no file names are specified, create them.
        If Fileargs.Length < 2 Then
            dataFile = "text.txt"
            signedFile = "signedFile.enc"

            If Not File.Exists(dataFile) Then
                ' Create a file to write to.
                Using sw As StreamWriter = File.CreateText(dataFile)
                    sw.WriteLine("Here is a message to sign")
                End Using
            End If

        Else
            dataFile = Fileargs(0)
            signedFile = Fileargs(1)
        End If
        Try
            ' Create a random key using a random number generator. This would be the
            '  secret key shared by sender and receiver.
            Dim secretkey() As Byte = New [Byte](63) {}
            'RNGCryptoServiceProvider is an implementation of a random number generator.
            Using rng As New RNGCryptoServiceProvider()
                ' The array is now filled with cryptographically strong random bytes.
                rng.GetBytes(secretkey)

                ' Use the secret key to encode the message file.
                SignFile(secretkey, dataFile, signedFile)

                ' Take the encoded file and decode
                VerifyFile(secretkey, signedFile)
            End Using
        Catch e As IOException
            Console.WriteLine("Error: File not found", e)
        End Try

    End Sub

    ' Computes a keyed hash for a source file and creates a target file with the keyed hash
    ' prepended to the contents of the source file. 
    Public Shared Sub SignFile(ByVal key() As Byte, ByVal sourceFile As String, ByVal destFile As String)
        ' Initialize the keyed hash object.
        Using myhmac As New HMACSHA256(key)
            Using inStream As New FileStream(sourceFile, FileMode.Open)
                Using outStream As New FileStream(destFile, FileMode.Create)
                    ' Compute the hash of the input file.
                    Dim hashValue As Byte() = myhmac.ComputeHash(inStream)
                    ' Reset inStream to the beginning of the file.
                    inStream.Position = 0
                    ' Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length)
                    ' Copy the contents of the sourceFile to the destFile.
                    Dim bytesRead As Integer
                    ' read 1K at a time
                    Dim buffer(1023) As Byte
                    Do
                        ' Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024)
                        outStream.Write(buffer, 0, bytesRead)
                    Loop While bytesRead > 0
                End Using
            End Using
        End Using
        Return

    End Sub
    ' end SignFile

    ' Compares the key in the source file with a new key created for the data portion of the file. If the keys 
    ' compare the data has not been tampered with.
    Public Shared Function VerifyFile(ByVal key() As Byte, ByVal sourceFile As String) As Boolean
        Dim err As Boolean = False
        ' Initialize the keyed hash object. 
        Using hmac As New HMACSHA256(key)
            ' Create an array to hold the keyed hash value read from the file.
            Dim storedHash(hmac.HashSize / 8 - 1) As Byte
            ' Create a FileStream for the source file.
            Using inStream As New FileStream(sourceFile, FileMode.Open)
                ' Read in the storedHash.
                inStream.Read(storedHash, 0, storedHash.Length - 1)
                ' Compute the hash of the remaining contents of the file.
                ' The stream is properly positioned at the beginning of the content, 
                ' immediately after the stored hash value.
                Dim computedHash As Byte() = hmac.ComputeHash(inStream)
                ' compare the computed hash with the stored value
                Dim i As Integer
                For i = 0 To storedHash.Length - 2
                    If computedHash(i) <> storedHash(i) Then
                        err = True
                    End If
                Next i
            End Using
        End Using
        If err Then
            Console.WriteLine("Hash values differ! Signed file has been tampered with!")
            Return False
        Else
            Console.WriteLine("Hash values agree -- no tampering occurred.")
            Return True
        End If

    End Function 'VerifyFile 
End Class
'end class

Comentários

HMACSHA256 é um tipo de algoritmo de hash com chave que é construído a partir da função de hash SHA-256 e usado como um Message Authentication Code baseado em hash (HMAC).HMACSHA256 is a type of keyed hash algorithm that is constructed from the SHA-256 hash function and used as a Hash-based Message Authentication Code (HMAC). O processo HMAC combina uma chave secreta com os dados da mensagem, faz o hash do resultado com a função de hash, combina esse valor de hash com a chave secreta novamente e, em seguida, aplica a função de hash uma segunda vez.The HMAC process mixes a secret key with the message data, hashes the result with the hash function, mixes that hash value with the secret key again, and then applies the hash function a second time. O hash de saída tem 256 bits de comprimento.The output hash is 256 bits in length.

Um HMAC pode ser usado para determinar se uma mensagem enviada por um canal inseguro foi violada, desde que o remetente e o destinatário compartilhem uma chave secreta.An HMAC can be used to determine whether a message sent over an insecure channel has been tampered with, provided that the sender and receiver share a secret key. O remetente computa o valor de hash para os dados originais e envia os dados originais e o valor de hash como uma única mensagem.The sender computes the hash value for the original data and sends both the original data and hash value as a single message. O receptor recalcula o valor de hash na mensagem recebida e verifica se o HMAC calculado corresponde ao HMAC transmitido.The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

Qualquer alteração nos dados ou no valor de hash resulta em uma incompatibilidade, porque o conhecimento da chave secreta é necessário para alterar a mensagem e reproduzir o valor de hash correto.Any change to the data or the hash value results in a mismatch, because knowledge of the secret key is required to change the message and reproduce the correct hash value. Portanto, se os valores de hash original e computados corresponderem, a mensagem será autenticada.Therefore, if the original and computed hash values match, the message is authenticated.

HMACSHA256 aceita chaves de qualquer tamanho e produz uma sequência de hash de 256 bits de comprimento.HMACSHA256 accepts keys of any size, and produces a hash sequence 256 bits in length.

Construtores

HMACSHA256()

Inicializa uma nova instância da classe HMACSHA256 com uma chave gerada aleatoriamente.Initializes a new instance of the HMACSHA256 class with a randomly generated key.

HMACSHA256(Byte[])

Inicializa uma nova instância da classe HMACSHA256 com os dados de chave especificados.Initializes a new instance of the HMACSHA256 class with the specified key data.

Campos

HashSizeValue

Representa o tamanho, em bits, do código hash calculado.Represents the size, in bits, of the computed hash code.

(Herdado de HashAlgorithm)
HashValue

Representa o valor do código hash computado.Represents the value of the computed hash code.

(Herdado de HashAlgorithm)
KeyValue

A chave a ser usada no algoritmo de hash.The key to use in the hash algorithm.

(Herdado de KeyedHashAlgorithm)
State

Representa o estado do cálculo de hash.Represents the state of the hash computation.

(Herdado de HashAlgorithm)

Propriedades

BlockSizeValue

Obtém ou define o tamanho do bloco a ser usado no valor de hash.Gets or sets the block size to use in the hash value.

(Herdado de HMAC)
CanReuseTransform

Obtém um valor que indica se a transformação atual pode ser reutilizada.Gets a value indicating whether the current transform can be reused.

(Herdado de HashAlgorithm)
CanTransformMultipleBlocks

Quando substituído em uma classe derivada, obtém um valor que indica se vários blocos podem ser transformados.When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.

(Herdado de HashAlgorithm)
Hash

Obtém o valor do código hash computado.Gets the value of the computed hash code.

(Herdado de HashAlgorithm)
HashName

Obtém ou define o nome do algoritmo de hash a ser usado para hash.Gets or sets the name of the hash algorithm to use for hashing.

(Herdado de HMAC)
HashSize

Obtém o tamanho, em bits, do HMAC calculado.Gets the size, in bits, of the computed HMAC.

HashSize

Obtém o tamanho, em bits, do código hash computado.Gets the size, in bits, of the computed hash code.

(Herdado de HashAlgorithm)
InputBlockSize

Quando substituído em uma classe derivada, obtém o tamanho do bloco de entrada.When overridden in a derived class, gets the input block size.

(Herdado de HashAlgorithm)
Key

Obtém ou define a chave a ser usada no algoritmo HMAC.Gets or sets the key to use in the HMAC calculation.

Key

Obtém ou define a chave a ser usada no algoritmo HMAC.Gets or sets the key to use in the HMAC calculation.

(Herdado de HMAC)
OutputBlockSize

Quando substituído em uma classe derivada, obtém o tamanho do bloco de saída.When overridden in a derived class, gets the output block size.

(Herdado de HashAlgorithm)

Métodos

Clear()

Libera todos os recursos usados pela classe HashAlgorithm.Releases all resources used by the HashAlgorithm class.

(Herdado de HashAlgorithm)
ComputeHash(Byte[])

Calcula o valor do hash da matriz de bytes especificada.Computes the hash value for the specified byte array.

(Herdado de HashAlgorithm)
ComputeHash(Byte[], Int32, Int32)

Calcula o valor de hash para a região especificada da matriz de bytes especificada.Computes the hash value for the specified region of the specified byte array.

(Herdado de HashAlgorithm)
ComputeHash(Stream)

Calcula o valor do hash do objeto Stream especificado.Computes the hash value for the specified Stream object.

(Herdado de HashAlgorithm)
ComputeHashAsync(Stream, CancellationToken)

Calcula assincronamente o valor do hash do objeto Stream especificado.Asynchronously computes the hash value for the specified Stream object.

(Herdado de HashAlgorithm)
Dispose()

Libera todos os recursos usados pela instância atual da classe HashAlgorithm.Releases all resources used by the current instance of the HashAlgorithm class.

(Herdado de HashAlgorithm)
Dispose(Boolean)

Libera os recursos não gerenciados usados pelo HMACSHA256 e opcionalmente libera os recursos gerenciados.Releases the unmanaged resources used by the HMACSHA256 and optionally releases the managed resources.

Dispose(Boolean)

Libera os recursos não gerenciados usados pela classe HMAC quando uma alteração de chave é legítima e, opcionalmente, libera os recursos gerenciados.Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources.

(Herdado de HMAC)
Equals(Object)

Determina se o objeto especificado é igual ao objeto atual.Determines whether the specified object is equal to the current object.

(Herdado de Object)
GetHashCode()

Serve como a função de hash padrão.Serves as the default hash function.

(Herdado de Object)
GetType()

Obtém o Type da instância atual.Gets the Type of the current instance.

(Herdado de Object)
HashCore(Byte[], Int32, Int32)

Roteia os dados gravados no objeto para o algoritmo HMAC para cálculo do HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

HashCore(Byte[], Int32, Int32)

Quando substituído em uma classe derivada, roteia os dados gravados no objeto para o algoritmo HMAC para cálculo do valor de HMAC.When overridden in a derived class, routes data written to the object into the HMAC algorithm for computing the HMAC value.

(Herdado de HMAC)
HashCore(ReadOnlySpan<Byte>)

Roteia os dados gravados no objeto para o algoritmo HMAC para cálculo do HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

HashCore(ReadOnlySpan<Byte>)

Roteia os dados gravados no objeto para o algoritmo HMAC para cálculo do HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

(Herdado de HMAC)
HashFinal()

Finaliza o cálculo de HMAC depois que os últimos dados são processados pelo algoritmo.Finalizes the HMAC computation after the last data is processed by the algorithm.

HashFinal()

Quando substituído em uma classe derivada, finaliza o cálculo de HMAC depois que os últimos dados são processados pelo algoritmo.When overridden in a derived class, finalizes the HMAC computation after the last data is processed by the algorithm.

(Herdado de HMAC)
Initialize()

Redefine o algoritmo de hash para o estado inicial.Resets the hash algorithm to its initial state.

Initialize()

Inicializa uma nova instância da implementação padrão do HMAC.Initializes an instance of the default implementation of HMAC.

(Herdado de HMAC)
MemberwiseClone()

Cria uma cópia superficial do Object atual.Creates a shallow copy of the current Object.

(Herdado de Object)
ToString()

Retorna uma cadeia de caracteres que representa o objeto atual.Returns a string that represents the current object.

(Herdado de Object)
TransformBlock(Byte[], Int32, Int32, Byte[], Int32)

Calcula o valor de hash para a região especificada da matriz de bytes de entrada e copia a região especificada da matriz de bytes de entrada para a região especificada da matriz de bytes de saída.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.

(Herdado de HashAlgorithm)
TransformFinalBlock(Byte[], Int32, Int32)

Calcula o valor de hash para a região especificada da matriz de bytes especificada.Computes the hash value for the specified region of the specified byte array.

(Herdado de HashAlgorithm)
TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32)

Tenta calcular o valor de hash para a matriz de bytes especificada.Attempts to compute the hash value for the specified byte array.

(Herdado de HashAlgorithm)
TryHashFinal(Span<Byte>, Int32)

Tenta finalizar o cálculo de HMAC depois que os últimos dados são processados pelo algoritmo HMAC.Attempts to finalize the HMAC computation after the last data is processed by the HMAC algorithm.

TryHashFinal(Span<Byte>, Int32)

Tenta finalizar o cálculo de HMAC depois que os últimos dados são processados pelo algoritmo HMAC.Attempts to finalize the HMAC computation after the last data is processed by the HMAC algorithm.

(Herdado de HMAC)

Implantações explícitas de interface

IDisposable.Dispose()

Libera os recursos não gerenciados usados pelo HashAlgorithm e opcionalmente libera os recursos gerenciados.Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources.

(Herdado de HashAlgorithm)

Aplica-se a