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11/18/2011

HMACSHA1 Class

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Computes a Hash-based Message Authentication Code (HMAC) using the SHA1 hash function.

Inheritance Hierarchy

System.Object
  System.Security.Cryptography.HashAlgorithm
    System.Security.Cryptography.KeyedHashAlgorithm
      System.Security.Cryptography.HMAC
        System.Security.Cryptography.HMACSHA1

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Class HMACSHA1 _
    Inherits HMAC

[ComVisibleAttribute(true)]
public class HMACSHA1 : HMAC

The HMACSHA1 type exposes the following members.

Constructors

	Name	Description
	HMACSHA1()	Initializes a new instance of the HMACSHA1 class with a randomly generated key.
	HMACSHA1(array<Byte[])	Initializes a new instance of the HMACSHA1 class with the specified key data.

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Properties

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

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Methods

	Name	Description
	Clear	Releases all resources used by the HashAlgorithm class. (Inherited from HashAlgorithm.)
	ComputeHash(array<Byte[])	Computes the hash value for the specified byte array. (Inherited from HashAlgorithm.)
	ComputeHash(Stream)	Computes the hash value for the specified Stream object. (Inherited from HashAlgorithm.)
	ComputeHash(array<Byte[], Int32, Int32)	Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm.)
	Dispose	Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources. (Inherited from HMAC.)
	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 the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	HashCore	When overridden in a derived class, routes data written to the object into the default HMAC hash algorithm for computing the hash value. (Inherited from HMAC.)
	HashFinal	When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object. (Inherited from HMAC.)
	Initialize	Initializes an instance of the default implementation of HMAC. (Inherited from HMAC.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	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.)
	TransformFinalBlock	Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm.)

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Fields

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

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Explicit Interface Implementations

	Name	Description
	IDisposable.Dispose	Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources. (Inherited from HashAlgorithm.)

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Remarks

HMACSHA1 is a type of keyed hash algorithm that is constructed from the SHA1 hash function and used as an HMAC, or hash-based message authentication code. The HMAC process consists of the following four steps:

Mixes a secret key with the message data.
Hashes the result with the hash function.
Mixes that hash value with the secret key again.
Then applies the hash function a second time.

The output hash is 160 bits in length.

An 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 hash value as a single message. The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

Any change to the data or the hash value will result 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.

The SHA-1 (Secure Hash Algorithm, also called SHS, Secure Hash Standard) is a cryptographic hash algorithm published by the United States Government. It produces a 160-bit hash value from an arbitrary length string.

HMACSHA1 accepts keys of any size, and produces a hash sequence of length 160 bits.

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.

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