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SymmetricAlgorithm Class

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

Inheritance Hierarchy

System.Object
  System.Security.Cryptography.SymmetricAlgorithm
    System.Security.Cryptography.Aes

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

Syntax

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

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

The SymmetricAlgorithm type exposes the following members.

Constructors

  Name Description
Protected methodSupported by Silverlight for Windows Phone SymmetricAlgorithm Initializes a new instance of the SymmetricAlgorithm class.

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Properties

  Name Description
Public propertySupported by Silverlight for Windows Phone BlockSize Gets or sets the block size, in bits, of the cryptographic operation.
Public propertySupported by Silverlight for Windows Phone IV Gets or sets the initialization vector (IV) for the symmetric algorithm.
Public propertySupported by Silverlight for Windows Phone Key Gets or sets the secret key for the symmetric algorithm.
Public propertySupported by Silverlight for Windows Phone KeySize Gets or sets the size, in bits, of the secret key used by the symmetric algorithm.
Public propertySupported by Silverlight for Windows Phone LegalBlockSizes Gets the block sizes, in bits, that are supported by the symmetric algorithm.
Public propertySupported by Silverlight for Windows Phone LegalKeySizes Gets the key sizes, in bits, that are supported by the symmetric algorithm.

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Methods

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

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Fields

  Name Description
Protected fieldSupported by Silverlight for Windows Phone BlockSizeValue Represents the block size, in bits, of the cryptographic operation.
Protected fieldSupported by Silverlight for Windows Phone IVValue Represents the initialization vector (IV) for the symmetric algorithm.
Protected fieldSupported by Silverlight for Windows Phone KeySizeValue Represents the size, in bits, of the secret key used by the symmetric algorithm.
Protected fieldSupported by Silverlight for Windows Phone KeyValue Represents the secret key for the symmetric algorithm.
Protected fieldSupported by Silverlight for Windows Phone LegalBlockSizesValue Specifies the block sizes, in bits, that are supported by the symmetric algorithm.
Protected fieldSupported by Silverlight for Windows Phone LegalKeySizesValue Specifies the key sizes, in bits, that are supported by the symmetric algorithm.

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Explicit Interface Implementations

  Name Description
Explicit interface implemetationPrivate methodSupported by Silverlight for Windows Phone IDisposable.Dispose Infrastructure. Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources.

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Remarks

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.

AesManaged is an implementation of the SymmetricAlgorithm class.

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.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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.