HMACSHA256 Clase

Definición

Calcula un código de autenticación de mensajes basado en hash (HMAC) mediante la función 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
Herencia
Atributos

Ejemplos

En el ejemplo siguiente se muestra cómo firmar un archivo mediante el HMACSHA256 objeto y cómo comprobar el archivo.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

Comentarios

HMACSHA256 es un tipo de algoritmo hash con clave que se construye a partir de la función hash SHA-256 y se utiliza como un código de autentificación de mensajes (MAC) basado en 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). El proceso HMAC combina una clave secreta con los datos del mensaje, aplica un algoritmo hash al resultado con la función hash, combina ese valor hash con la clave secreta y, a continuación, aplica la función hash por 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. El hash de salida tiene una longitud de 256 bits.The output hash is 256 bits in length.

Un HMAC se puede usar para determinar si se ha alterado un mensaje enviado a través de un canal no seguro, siempre que el remitente y el receptor compartan una clave 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. El remitente calcula el valor hash de los datos originales y envía los datos originales y el valor hash como un solo mensaje.The sender computes the hash value for the original data and sends both the original data and hash value as a single message. El receptor vuelve a calcular el valor hash del mensaje recibido y comprueba que el HMAC calculado coincide con el HMAC transmitido.The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

Cualquier cambio en los datos o en el valor hash produce una falta de coincidencia, ya que el conocimiento de la clave secreta es necesario para cambiar el mensaje y reproducir el valor hash correcto.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. Por lo tanto, si los valores hash originales y calculados coinciden, el mensaje se autentica.Therefore, if the original and computed hash values match, the message is authenticated.

HMACSHA256 acepta claves de cualquier tamaño y genera una secuencia hash de 256 bits de longitud.HMACSHA256 accepts keys of any size, and produces a hash sequence 256 bits in length.

Constructores

HMACSHA256()

Inicializa una nueva instancia de la clase HMACSHA256 con una clave generada aleatoriamente.Initializes a new instance of the HMACSHA256 class with a randomly generated key.

HMACSHA256(Byte[])

Inicializa una nueva instancia de la clase HMACSHA256 con los datos de clave especificados.Initializes a new instance of the HMACSHA256 class with the specified key data.

Campos

HashSizeValue

Representa el tamaño en bits del código hash calculado.Represents the size, in bits, of the computed hash code.

(Heredado de HashAlgorithm)
HashValue

Representa el valor del código hash calculado.Represents the value of the computed hash code.

(Heredado de HashAlgorithm)
KeyValue

Clave que se va a usar en el algoritmo hash.The key to use in the hash algorithm.

(Heredado de KeyedHashAlgorithm)
State

Representa el estado del cálculo del valor hash.Represents the state of the hash computation.

(Heredado de HashAlgorithm)

Propiedades

BlockSizeValue

Obtiene o establece el tamaño de bloque que se va a usar en el valor hash.Gets or sets the block size to use in the hash value.

(Heredado de HMAC)
CanReuseTransform

Obtiene un valor que indica si la transformación actual puede volver a usarse.Gets a value indicating whether the current transform can be reused.

(Heredado de HashAlgorithm)
CanTransformMultipleBlocks

Cuando se invalida en una clase derivada, obtiene un valor que indica si se pueden transformar varios bloques.When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.

(Heredado de HashAlgorithm)
Hash

Obtiene el valor del código hash calculado.Gets the value of the computed hash code.

(Heredado de HashAlgorithm)
HashName

Obtiene o establece el nombre del algoritmo hash que se va a utilizar para la operación hash.Gets or sets the name of the hash algorithm to use for hashing.

(Heredado de HMAC)
HashSize

Obtiene el tamaño en bits del HMAC calculado.Gets the size, in bits, of the computed HMAC.

HashSize

Obtiene el tamaño en bits del código hash calculado.Gets the size, in bits, of the computed hash code.

(Heredado de HashAlgorithm)
InputBlockSize

Cuando se invalida en una clase derivada, obtiene el tamaño del bloque de entrada.When overridden in a derived class, gets the input block size.

(Heredado de HashAlgorithm)
Key

Obtiene o establece la clave que se va a usar en el cálculo de HMAC.Gets or sets the key to use in the HMAC calculation.

Key

Obtiene o establece la clave que se va a usar en el cálculo de HMAC.Gets or sets the key to use in the HMAC calculation.

(Heredado de HMAC)
OutputBlockSize

Cuando se invalida en una clase derivada, obtiene el tamaño del bloque de salida.When overridden in a derived class, gets the output block size.

(Heredado de HashAlgorithm)

Métodos

Clear()

Libera todos los recursos que utiliza la clase HashAlgorithm.Releases all resources used by the HashAlgorithm class.

(Heredado de HashAlgorithm)
ComputeHash(Byte[])

Calcula el valor hash para la matriz de bytes especificada.Computes the hash value for the specified byte array.

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

Calcula el valor hash para la región especificada de la matriz de bytes indicada.Computes the hash value for the specified region of the specified byte array.

(Heredado de HashAlgorithm)
ComputeHash(Stream)

Calcula el valor hash del objeto Stream especificado.Computes the hash value for the specified Stream object.

(Heredado de HashAlgorithm)
ComputeHashAsync(Stream, CancellationToken)

Calcula de manera asincrónica el valor hash del objeto Stream especificado.Asynchronously computes the hash value for the specified Stream object.

(Heredado de HashAlgorithm)
Dispose()

Libera todos los recursos usados por la instancia actual de la clase HashAlgorithm.Releases all resources used by the current instance of the HashAlgorithm class.

(Heredado de HashAlgorithm)
Dispose(Boolean)

Libera los recursos no administrados que usa HMACSHA256 y, de forma opcional, libera los recursos administrados.Releases the unmanaged resources used by the HMACSHA256 and optionally releases the managed resources.

Dispose(Boolean)

Libera los recursos no administrados que usa la clase HMAC cuando un cambio de clave es legítimo y, opcionalmente, libera los recursos administrados.Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources.

(Heredado de HMAC)
Equals(Object)

Determina si el objeto especificado es igual que el objeto actual.Determines whether the specified object is equal to the current object.

(Heredado de Object)
GetHashCode()

Sirve como la función hash predeterminada.Serves as the default hash function.

(Heredado de Object)
GetType()

Obtiene el Type de la instancia actual.Gets the Type of the current instance.

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

Envía los datos escritos en el objeto al algoritmo HMAC para el cálculo del HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

HashCore(Byte[], Int32, Int32)

Cuando se invalida en una clase derivada, enruta los datos escritos en el objeto al algoritmo HMAC para el cálculo del valor de HMAC.When overridden in a derived class, routes data written to the object into the HMAC algorithm for computing the HMAC value.

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

Envía los datos escritos en el objeto al algoritmo HMAC para el cálculo del HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

HashCore(ReadOnlySpan<Byte>)

Envía los datos escritos en el objeto al algoritmo HMAC para el cálculo del HMAC.Routes data written to the object into the HMAC algorithm for computing the HMAC.

(Heredado de HMAC)
HashFinal()

Finaliza el cálculo de HMAC una vez que el algoritmo procesa los últimos datos.Finalizes the HMAC computation after the last data is processed by the algorithm.

HashFinal()

Cuando se invalida en una clase derivada, finaliza el cálculo de HMAC una vez que el algoritmo termina de procesar los últimos datos.When overridden in a derived class, finalizes the HMAC computation after the last data is processed by the algorithm.

(Heredado de HMAC)
Initialize()

Restablece el algoritmo hash a su estado inicial.Resets the hash algorithm to its initial state.

Initialize()

Inicializa una instancia de la implementación predeterminada de HMAC.Initializes an instance of the default implementation of HMAC.

(Heredado de HMAC)
MemberwiseClone()

Crea una copia superficial del Object actual.Creates a shallow copy of the current Object.

(Heredado de Object)
ToString()

Devuelve una cadena que representa el objeto actual.Returns a string that represents the current object.

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

Calcula el valor hash para la región especificada de la matriz de bytes de entrada y copia la región especificada de la matriz de bytes de entrada resultante en la región indicada de la matriz de bytes de salida.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.

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

Calcula el valor hash para la región especificada de la matriz de bytes indicada.Computes the hash value for the specified region of the specified byte array.

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

Intenta calcular el valor de hash para la matriz de bytes especificada.Attempts to compute the hash value for the specified byte array.

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

Intenta finalizar el cálculo de HMAC una vez que el algoritmo HMAC procesa los últimos datos.Attempts to finalize the HMAC computation after the last data is processed by the HMAC algorithm.

TryHashFinal(Span<Byte>, Int32)

Intenta finalizar el cálculo de HMAC una vez que el algoritmo HMAC procesa los últimos datos.Attempts to finalize the HMAC computation after the last data is processed by the HMAC algorithm.

(Heredado de HMAC)

Implementaciones de interfaz explícitas

IDisposable.Dispose()

Libera los recursos no administrados que usa HashAlgorithm y, de forma opcional, libera los recursos administrados.Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources.

(Heredado de HashAlgorithm)

Se aplica a