HMACSHA384 Class

 

Computes a Hash-based Message Authentication Code (HMAC) using the SHA384 hash function.

Namespace:   System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)


[ComVisibleAttribute(true)]
public ref class HMACSHA384 : HMAC

NameDescription
System_CAPS_pubmethodHMACSHA384()

Initializes a new instance of the HMACSHA384 class by using a randomly generated key.

System_CAPS_pubmethodHMACSHA384(array<Byte>^)

Initializes a new instance of the HMACSHA384 class by using the specified key data.

NameDescription
System_CAPS_protpropertyBlockSizeValue

Gets or sets the block size to use in the hash value.(Inherited from HMAC.)

System_CAPS_pubpropertyCanReuseTransform

Gets a value indicating whether the current transform can be reused.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyCanTransformMultipleBlocks

When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyHash

Gets the value of the computed hash code.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyHashName

Gets or sets the name of the hash algorithm to use for hashing.(Inherited from HMAC.)

System_CAPS_pubpropertyHashSize

Gets the size, in bits, of the computed hash code.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyInputBlockSize

When overridden in a derived class, gets the input block size.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyKey

Gets or sets the key to use in the hash algorithm.(Inherited from HMAC.)

System_CAPS_pubpropertyOutputBlockSize

When overridden in a derived class, gets the output block size.(Inherited from HashAlgorithm.)

System_CAPS_pubpropertyProduceLegacyHmacValues

Provides a workaround for the .NET Framework 2.0 implementation of the HMACSHA384 algorithm, which is inconsistent with the .NET Framework 2.0 Service Pack 1 implementation of the algorithm.

NameDescription
System_CAPS_pubmethodClear()

Releases all resources used by the HashAlgorithm class.(Inherited from HashAlgorithm.)

System_CAPS_pubmethodComputeHash(array<Byte>^)

Computes the hash value for the specified byte array.(Inherited from HashAlgorithm.)

System_CAPS_pubmethodComputeHash(array<Byte>^, Int32, Int32)

Computes the hash value for the specified region of the specified byte array.(Inherited from HashAlgorithm.)

System_CAPS_pubmethodComputeHash(Stream^)

Computes the hash value for the specified Stream object.(Inherited from HashAlgorithm.)

System_CAPS_pubmethodDispose()

Releases all resources used by the current instance of the HashAlgorithm class.(Inherited from HashAlgorithm.)

System_CAPS_protmethodDispose(Boolean)

Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources.(Inherited from HMAC.)

System_CAPS_pubmethodEquals(Object^)

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_protmethodFinalize()

Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_protmethodHashCore(array<Byte>^, Int32, Int32)

When overridden in a derived class, routes data written to the object into the default HMAC hash algorithm for computing the hash value.(Inherited from HMAC.)

System_CAPS_protmethodHashFinal()

When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object.(Inherited from HMAC.)

System_CAPS_pubmethodInitialize()

Initializes an instance of the default implementation of HMAC.(Inherited from HMAC.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_pubmethodToString()

Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubmethodTransformBlock(array<Byte>^, Int32, Int32, array<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.)

System_CAPS_pubmethodTransformFinalBlock(array<Byte>^, Int32, Int32)

Computes the hash value for the specified region of the specified byte array.(Inherited from HashAlgorithm.)

NameDescription
System_CAPS_protfieldHashSizeValue

Represents the size, in bits, of the computed hash code.(Inherited from HashAlgorithm.)

System_CAPS_protfieldHashValue

Represents the value of the computed hash code.(Inherited from HashAlgorithm.)

System_CAPS_protfieldKeyValue

The key to use in the hash algorithm.(Inherited from KeyedHashAlgorithm.)

System_CAPS_protfieldState

Represents the state of the hash computation.(Inherited from HashAlgorithm.)

HMACSHA384 is a type of keyed hash algorithm that is constructed from the SHA-384 hash function and used as a Hash-based Message Authentication Code (HMAC). The HMAC process mixes a secret key with the message data and hashes the result. The hash value is mixed with the secret key again, and then hashed a second time. The output hash is 384 bits long.

An HMAC can be used to determine whether a message sent over a nonsecure channel has been tampered with, provided that the sender and receiver share a secret key. The sender computes the hash value for the original data and sends both the original data and the hash value as a single message. The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

If the original and computed hash values match, the message is authenticated. If they do not match, either the data or the hash value has been changed. HMACs provide security against tampering because knowledge of the secret key is required to change the message and reproduce the correct hash value.

HMACSHA384 accepts all key sizes and produces a hash sequence that is 384 bits long.

The following example shows how to sign a file by using the HMACSHA384 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 decrypts the file and compares
// the source and the decrypted files.
void EncodeFile( array<Byte>^key, String^ sourceFile, String^ destFile )
{

   // Initialize the keyed hash object.
   HMACSHA384^ myhmacsha384 = gcnew HMACSHA384( 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 = myhmacsha384->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 );

   myhmacsha384->Clear();

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



// Decrypt the encoded file and compare to original file.
bool DecodeFile( array<Byte>^key, String^ sourceFile )
{

   // Initialize the keyed hash object. 
   HMACSHA384^ hmacsha384 = gcnew HMACSHA384( key );

   // Create an array to hold the keyed hash value read from the file.
   array<Byte>^storedHash = gcnew array<Byte>(hmacsha384->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 = hmacsha384->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: HMACSHA384 inputfile.txt encryptedfile.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


.NET Framework
Available since 2.0

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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