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HMAC Class

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)

[ComVisibleAttribute(true)] 
public abstract class HMAC : KeyedHashAlgorithm
/** @attribute ComVisibleAttribute(true) */ 
public abstract class HMAC extends KeyedHashAlgorithm
ComVisibleAttribute(true) 
public abstract class HMAC extends KeyedHashAlgorithm
Not applicable.

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.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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