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HMAC Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents the abstract class from which all implementations of Hash-based Message Authentication Code (HMAC) must derive.

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class HMAC _
    Inherits KeyedHashAlgorithm
[ComVisibleAttribute(true)]
public abstract class HMAC : KeyedHashAlgorithm

The HMAC type exposes the following members.

Constructors

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

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Properties

  Name Description
Protected propertySupported by Silverlight for Windows Phone BlockSizeValue Gets or sets the block size to use in the hash value.
Public propertySupported by Silverlight for Windows Phone CanReuseTransform Gets a value indicating whether the current transform can be reused. (Inherited from HashAlgorithm.)
Public propertySupported by Silverlight for Windows Phone CanTransformMultipleBlocks When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed. (Inherited from HashAlgorithm.)
Public propertySupported by Silverlight for Windows Phone Hash Gets the value of the computed hash code. (Inherited from HashAlgorithm.)
Public propertySupported by Silverlight for Windows Phone HashName Gets or sets the name of the hash algorithm to use for hashing.
Public propertySupported by Silverlight for Windows Phone HashSize Gets the size, in bits, of the computed hash code. (Inherited from HashAlgorithm.)
Public propertySupported by Silverlight for Windows Phone InputBlockSize When overridden in a derived class, gets the input block size. (Inherited from HashAlgorithm.)
Public propertySupported by Silverlight for Windows Phone Key Gets or sets the key to use in the hash algorithm. (Overrides KeyedHashAlgorithm.Key.)
Public propertySupported by Silverlight for Windows Phone OutputBlockSize When overridden in a derived class, gets the output block size. (Inherited from HashAlgorithm.)

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Methods

  Name Description
Public methodSupported by Silverlight for Windows Phone Clear Releases all resources used by the HashAlgorithm class. (Inherited from HashAlgorithm.)
Public methodSupported by Silverlight for Windows Phone ComputeHash(array<Byte[]) Computes the hash value for the specified byte array. (Inherited from HashAlgorithm.)
Public methodSupported by Silverlight for Windows Phone ComputeHash(Stream) Computes the hash value for the specified Stream object. (Inherited from HashAlgorithm.)
Public methodSupported by Silverlight for Windows Phone ComputeHash(array<Byte[], Int32, Int32) Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm.)
Protected methodSupported by Silverlight for Windows Phone Dispose Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources. (Overrides KeyedHashAlgorithm.Dispose(Boolean).)
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 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 HashCore When overridden in a derived class, routes data written to the object into the default HMAC hash algorithm for computing the hash value. (Overrides HashAlgorithm.HashCore(array<Byte[], Int32, Int32).)
Protected methodSupported by Silverlight for Windows Phone HashFinal When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object. (Overrides HashAlgorithm.HashFinal().)
Public methodSupported by Silverlight for Windows Phone Initialize Initializes an instance of the default implementation of HMAC. (Overrides HashAlgorithm.Initialize().)
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 TransformBlock Computes the hash value for the specified region of the input byte array and copies the resulting hash value to the specified region of the output byte array. (Inherited from HashAlgorithm.)
Public methodSupported by Silverlight for Windows Phone TransformFinalBlock Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm.)

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Fields

  Name Description
Protected fieldSupported by Silverlight for Windows Phone HashSizeValue Represents the size, in bits, of the computed hash code. (Inherited from HashAlgorithm.)
Protected fieldSupported by Silverlight for Windows Phone HashValue Represents the value of the computed hash code. (Inherited from HashAlgorithm.)
Protected fieldSupported by Silverlight for Windows Phone KeyValue The key to use in the hash algorithm. (Inherited from KeyedHashAlgorithm.)
Protected fieldSupported by Silverlight for Windows Phone State Represents the state of the hash computation. (Inherited from HashAlgorithm.)

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Explicit Interface Implementations

  Name Description
Explicit interface implemetationPrivate methodSupported by Silverlight for Windows Phone IDisposable.Dispose Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources. (Inherited from HashAlgorithm.)

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Remarks

A Hash-based Message Authentication Code (HMAC) can be used to determine whether a message sent over an insecure 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 HMAC as a single message. The receiver recomputes the hash value on the received message and checks that the computed hash value matches the transmitted hash value.

HMAC can be used with any iterative cryptographic hash function, such as MD5 or SHA-1, in combination with a secret shared key. The cryptographic strength of HMAC depends on the properties of the underlying hash function.

Any change to the data or the hash value results in a mismatch, because knowledge of the secret key is required to change the message and reproduce the correct hash value. Therefore, if the original and computed hash values match, the message is authenticated.

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.