SymmetricAlgorithm Class

.NET Framework (current version)

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Represents the abstract base class from which all implementations of symmetric algorithms must inherit.

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

Inheritance Hierarchy

System::Object
System.Security.Cryptography::SymmetricAlgorithm
System.Security.Cryptography::Aes
System.Security.Cryptography::DES
System.Security.Cryptography::RC2
System.Security.Cryptography::Rijndael
System.Security.Cryptography::TripleDES

Syntax

C++

[ComVisibleAttribute(true)]
public ref class SymmetricAlgorithm abstract : IDisposable

Constructors

	Name	Description
	SymmetricAlgorithm()	Initializes a new instance of the SymmetricAlgorithm class.

Properties

	Name	Description
	BlockSize	Gets or sets the block size, in bits, of the cryptographic operation.
	FeedbackSize	Gets or sets the feedback size, in bits, of the cryptographic operation.
	IV	Gets or sets the initialization vector (IV) for the symmetric algorithm.
	Key	Gets or sets the secret key for the symmetric algorithm.
	KeySize	Gets or sets the size, in bits, of the secret key used by the symmetric algorithm.
	LegalBlockSizes	Gets the block sizes, in bits, that are supported by the symmetric algorithm.
	LegalKeySizes	Gets the key sizes, in bits, that are supported by the symmetric algorithm.
	Mode	Gets or sets the mode for operation of the symmetric algorithm.
	Padding	Gets or sets the padding mode used in the symmetric algorithm.

Methods

	Name	Description
	Clear()	Releases all resources used by the SymmetricAlgorithm class.
	Create()	Creates a default cryptographic object used to perform the symmetric algorithm.
	Create(String^)	Creates the specified cryptographic object used to perform the symmetric algorithm.
	CreateDecryptor()	Creates a symmetric decryptor object with the current Key property and initialization vector (IV).
	CreateDecryptor(array<Byte>^, array<Byte>^)	When overridden in a derived class, creates a symmetric decryptor object with the specified Key property and initialization vector (IV).
	CreateEncryptor()	Creates a symmetric encryptor object with the current Key property and initialization vector (IV).
	CreateEncryptor(array<Byte>^, array<Byte>^)	When overridden in a derived class, creates a symmetric encryptor object with the specified Key property and initialization vector (IV).
	Dispose()	Releases all resources used by the current instance of the SymmetricAlgorithm class.
	Dispose(Boolean)	Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources.
	Equals(Object^)	Determines whether the specified object is equal to the current object.(Inherited from Object.)
	Finalize()	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)
	GenerateIV()	When overridden in a derived class, generates a random initialization vector (IV) to use for the algorithm.
	GenerateKey()	When overridden in a derived class, generates a random key (Key) to use for the algorithm.
	GetHashCode()	Serves as the default hash function. (Inherited from Object.)
	GetType()	Gets the Type of the current instance.(Inherited from Object.)
	MemberwiseClone()	Creates a shallow copy of the current Object.(Inherited from Object.)
	ToString()	Returns a string that represents the current object.(Inherited from Object.)
	ValidKeySize(Int32)	Determines whether the specified key size is valid for the current algorithm.

Fields

	Name	Description
	BlockSizeValue	Represents the block size, in bits, of the cryptographic operation.
	FeedbackSizeValue	Represents the feedback size, in bits, of the cryptographic operation.
	IVValue	Represents the initialization vector (IV) for the symmetric algorithm.
	KeySizeValue	Represents the size, in bits, of the secret key used by the symmetric algorithm.
	KeyValue	Represents the secret key for the symmetric algorithm.
	LegalBlockSizesValue	Specifies the block sizes, in bits, that are supported by the symmetric algorithm.
	LegalKeySizesValue	Specifies the key sizes, in bits, that are supported by the symmetric algorithm.
	ModeValue	Represents the cipher mode used in the symmetric algorithm.
	PaddingValue	Represents the padding mode used in the symmetric algorithm.

The classes that derive from the SymmetricAlgorithm class use a chaining mode called cipher block chaining (CBC), which requires a key (Key) and an initialization vector (IV) to perform cryptographic transformations on data. To decrypt data that was encrypted using one of the SymmetricAlgorithm classes, you must set the Key property and the IV property to the same values that were used for encryption. For a symmetric algorithm to be useful, the secret key must be known only to the sender and the receiver.

RijndaelManaged, DESCryptoServiceProvider, RC2CryptoServiceProvider, and TripleDESCryptoServiceProvider are implementations of symmetric algorithms.

Note that when using derived classes, it is not enough, from a security perspective, to simply force a garbage collection after you have finished using the object. You must explicitly call the Clear method on the object to zero out any sensitive data within the object before it is released. Note that garbage collection does not zero out the contents of collected objects but simply marks the memory as available for reallocation. Thus the data contained within a garbage collected object may still be present in the memory heap in unallocated memory. In the case of cryptographic objects, this data could contain sensitive information such as key data or a block of plain text.

All cryptographic classes in the .NET Framework that hold sensitive data implement a Clear method. When called, the Clear method overwrites all sensitive data within the object with zeros and then releases the object so that it can be safely garbage collected. When the object has been zeroed and released, you should then call the Dispose method with the disposing parameter set to True to dispose of all managed and unmanaged resources associated with the object.

Notes to Inheritors:

When you inherit from the SymmetricAlgorithm class, you must override the following members: CreateDecryptor, CreateEncryptor, GenerateIV, and GenerateKey.

Examples

The following code example uses the RijndaelManaged class with the specified Key property and initialization vector (IV) to encrypt a file specified by inName, and outputs the encrypted result to the file specified by outName. The desKey and desIV parameters to the method are 8-byte arrays. You must have the high encryption pack installed to run this example.

C++

void EncryptData( String^ inName, String^ outName, array<Byte>^rijnKey, array<Byte>^rijnIV )
{

   //Create the file streams to handle the input and output files.
   FileStream^ fin = gcnew FileStream( inName,FileMode::Open,FileAccess::Read );
   FileStream^ fout = gcnew FileStream( outName,FileMode::OpenOrCreate,FileAccess::Write );
   fout->SetLength( 0 );

   //Create variables to help with read and write.
   array<Byte>^bin = gcnew array<Byte>(100);
   long rdlen = 0; //This is the total number of bytes written.

   long totlen = (long)fin->Length; //This is the total length of the input file.

   int len; //This is the number of bytes to be written at a time.

   SymmetricAlgorithm^ rijn = SymmetricAlgorithm::Create(); //Creates the default implementation, which is RijndaelManaged.         

   CryptoStream^ encStream = gcnew CryptoStream( fout,rijn->CreateEncryptor( rijnKey, rijnIV ),CryptoStreamMode::Write );
   Console::WriteLine( "Encrypting..." );

   //Read from the input file, then encrypt and write to the output file.
   while ( rdlen < totlen )
   {
      len = fin->Read( bin, 0, 100 );
      encStream->Write( bin, 0, len );
      rdlen = rdlen + len;
      Console::WriteLine( "{0} bytes processed", rdlen );
   }

   encStream->Close();
   fout->Close();
   fin->Close();
}

Version Information

.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0

Thread Safety

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