SymmetricAlgorithm Class
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SymmetricAlgorithm Class

 

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

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


<ComVisibleAttribute(True)>
Public MustInherit Class SymmetricAlgorithm
	Implements IDisposable

NameDescription
System_CAPS_protmethodSymmetricAlgorithm()

Initializes a new instance of the SymmetricAlgorithm class.

NameDescription
System_CAPS_pubpropertyBlockSize

Gets or sets the block size, in bits, of the cryptographic operation.

System_CAPS_pubpropertyFeedbackSize

Gets or sets the feedback size, in bits, of the cryptographic operation.

System_CAPS_pubpropertyIV

Gets or sets the initialization vector (IV) for the symmetric algorithm.

System_CAPS_pubpropertyKey

Gets or sets the secret key for the symmetric algorithm.

System_CAPS_pubpropertyKeySize

Gets or sets the size, in bits, of the secret key used by the symmetric algorithm.

System_CAPS_pubpropertyLegalBlockSizes

Gets the block sizes, in bits, that are supported by the symmetric algorithm.

System_CAPS_pubpropertyLegalKeySizes

Gets the key sizes, in bits, that are supported by the symmetric algorithm.

System_CAPS_pubpropertyMode

Gets or sets the mode for operation of the symmetric algorithm.

System_CAPS_pubpropertyPadding

Gets or sets the padding mode used in the symmetric algorithm.

NameDescription
System_CAPS_pubmethodClear()

Releases all resources used by the SymmetricAlgorithm class.

System_CAPS_pubmethodSystem_CAPS_staticCreate()

Creates a default cryptographic object used to perform the symmetric algorithm.

System_CAPS_pubmethodSystem_CAPS_staticCreate(String)

Creates the specified cryptographic object used to perform the symmetric algorithm.

System_CAPS_pubmethodCreateDecryptor()

Creates a symmetric decryptor object with the current Key property and initialization vector (IV).

System_CAPS_pubmethodCreateDecryptor(Byte(), Byte())

When overridden in a derived class, creates a symmetric decryptor object with the specified Key property and initialization vector (IV).

System_CAPS_pubmethodCreateEncryptor()

Creates a symmetric encryptor object with the current Key property and initialization vector (IV).

System_CAPS_pubmethodCreateEncryptor(Byte(), Byte())

When overridden in a derived class, creates a symmetric encryptor object with the specified Key property and initialization vector (IV).

System_CAPS_pubmethodDispose()

Releases all resources used by the current instance of the SymmetricAlgorithm class.

System_CAPS_protmethodDispose(Boolean)

Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources.

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_pubmethodGenerateIV()

When overridden in a derived class, generates a random initialization vector (IV) to use for the algorithm.

System_CAPS_pubmethodGenerateKey()

When overridden in a derived class, generates a random key (Key) to use for the algorithm.

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_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_pubmethodValidKeySize(Int32)

Determines whether the specified key size is valid for the current algorithm.

NameDescription
System_CAPS_protfieldBlockSizeValue

Represents the block size, in bits, of the cryptographic operation.

System_CAPS_protfieldFeedbackSizeValue

Represents the feedback size, in bits, of the cryptographic operation.

System_CAPS_protfieldIVValue

Represents the initialization vector (IV) for the symmetric algorithm.

System_CAPS_protfieldKeySizeValue

Represents the size, in bits, of the secret key used by the symmetric algorithm.

System_CAPS_protfieldKeyValue

Represents the secret key for the symmetric algorithm.

System_CAPS_protfieldLegalBlockSizesValue

Specifies the block sizes, in bits, that are supported by the symmetric algorithm.

System_CAPS_protfieldLegalKeySizesValue

Specifies the key sizes, in bits, that are supported by the symmetric algorithm.

System_CAPS_protfieldModeValue

Represents the cipher mode used in the symmetric algorithm.

System_CAPS_protfieldPaddingValue

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.

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.

   Private Shared Sub EncryptData(inName As String, outName As String, _
   rijnKey() As Byte, rijnIV() As Byte)

       'Create the file streams to handle the input and output files.
       Dim fin As New FileStream(inName, FileMode.Open, FileAccess.Read)
       Dim fout As New FileStream(outName, FileMode.OpenOrCreate, _
          FileAccess.Write)
       fout.SetLength(0)

       'Create variables to help with read and write.
       Dim bin(100) As Byte 'This is intermediate storage for the encryption.
       Dim rdlen As Long = 0 'This is the total number of bytes written.
       Dim totlen As Long = fin.Length 'Total length of the input file.
       Dim len As Integer 'This is the number of bytes to be written at a time.
       'Creates the default implementation, which is RijndaelManaged.
       Dim rijn As SymmetricAlgorithm = SymmetricAlgorithm.Create()
       Dim encStream As New 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 = Convert.ToInt32(rdlen + len)
           Console.WriteLine("{0} bytes processed", rdlen)
       End While

       encStream.Close()
fout.Close()
fin.Close()
   End Sub

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0

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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