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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)

[<AbstractClass>]
[<ComVisibleAttribute(true)>]
type SymmetricAlgorithm =  
    class 
        interface IDisposable 
    end

The SymmetricAlgorithm type exposes the following members.

  NameDescription
Protected methodSymmetricAlgorithmInitializes a new instance of the SymmetricAlgorithm class.
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  NameDescription
Public propertyBlockSizeGets or sets the block size, in bits, of the cryptographic operation.
Public propertyFeedbackSizeGets or sets the feedback size, in bits, of the cryptographic operation.
Public propertyIVGets or sets the initialization vector (IV) for the symmetric algorithm.
Public propertyKeyGets or sets the secret key for the symmetric algorithm.
Public propertyKeySizeGets or sets the size, in bits, of the secret key used by the symmetric algorithm.
Public propertyLegalBlockSizesGets the block sizes, in bits, that are supported by the symmetric algorithm.
Public propertyLegalKeySizesGets the key sizes, in bits, that are supported by the symmetric algorithm.
Public propertyModeGets or sets the mode for operation of the symmetric algorithm.
Public propertyPaddingGets or sets the padding mode used in the symmetric algorithm.
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  NameDescription
Public methodClearReleases all resources used by the SymmetricAlgorithm class.
Public methodStatic memberCreate()Creates a default cryptographic object used to perform the symmetric algorithm.
Public methodStatic memberCreate(String)Creates the specified cryptographic object used to perform the symmetric algorithm.
Public methodCreateDecryptor()Creates a symmetric decryptor object with the current Key property and initialization vector (IV).
Public methodCreateDecryptor(Byte[], Byte[])When overridden in a derived class, creates a symmetric decryptor object with the specified Key property and initialization vector (IV).
Public methodCreateEncryptor()Creates a symmetric encryptor object with the current Key property and initialization vector (IV).
Public methodCreateEncryptor(Byte[], Byte[])When overridden in a derived class, creates a symmetric encryptor object with the specified Key property and initialization vector (IV).
Public methodDispose()Releases all resources used by the current instance of the SymmetricAlgorithm class.
Protected methodDispose(Boolean)Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources.
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGenerateIVWhen overridden in a derived class, generates a random initialization vector (IV) to use for the algorithm.
Public methodGenerateKeyWhen overridden in a derived class, generates a random key (Key) to use for the algorithm.
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodValidKeySizeDetermines whether the specified key size is valid for the current algorithm.
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  NameDescription
Protected fieldBlockSizeValueRepresents the block size, in bits, of the cryptographic operation.
Protected fieldFeedbackSizeValueRepresents the feedback size, in bits, of the cryptographic operation.
Protected fieldIVValueRepresents the initialization vector (IV) for the symmetric algorithm.
Protected fieldKeySizeValueRepresents the size, in bits, of the secret key used by the symmetric algorithm.
Protected fieldKeyValueRepresents the secret key for the symmetric algorithm.
Protected fieldLegalBlockSizesValueSpecifies the block sizes, in bits, that are supported by the symmetric algorithm.
Protected fieldLegalKeySizesValueSpecifies the key sizes, in bits, that are supported by the symmetric algorithm.
Protected fieldModeValueRepresents the cipher mode used in the symmetric algorithm.
Protected fieldPaddingValueRepresents the padding mode used in the symmetric algorithm.
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  NameDescription
Explicit interface implemetationPrivate methodIDisposable.DisposeInfrastructure. Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources.
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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.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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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