HMAC Class

Definition

Namespace:

System.Security.Cryptography

Assembly:

System.Security.Cryptography.dll

Source:

HMAC.cs

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

public ref class HMAC abstract : System::Security::Cryptography::KeyedHashAlgorithm

public abstract class HMAC : System.Security.Cryptography.KeyedHashAlgorithm

type HMAC = class
    inherit KeyedHashAlgorithm

Public MustInherit Class HMAC
Inherits KeyedHashAlgorithm

Inheritance

Object

HashAlgorithm

KeyedHashAlgorithm

HMAC

Derived

System.Security.Cryptography.HMACMD5

System.Security.Cryptography.HMACRIPEMD160

System.Security.Cryptography.HMACSHA1

System.Security.Cryptography.HMACSHA256

System.Security.Cryptography.HMACSHA3_256

System.Security.Cryptography.HMACSHA3_384

System.Security.Cryptography.HMACSHA3_512

System.Security.Cryptography.HMACSHA384

System.Security.Cryptography.HMACSHA512

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.

Due to collision problems with MD5 and SHA-1, Microsoft recommends a security model based on SHA-256 or better.

Constructors

HMAC()

Initializes a new instance of the HMAC class.

Fields

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)

Properties

BlockSizeValue	Gets or sets the block size to use in the hash value.
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.
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 HMAC calculation.
OutputBlockSize	When overridden in a derived class, gets the output block size. (Inherited from HashAlgorithm)

Methods

Clear()	Releases all resources used by the HashAlgorithm class. (Inherited from HashAlgorithm)
ComputeHash(Byte[], Int32, Int32)	Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm)
ComputeHash(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)
ComputeHashAsync(Stream, CancellationToken)	Asynchronously computes the hash value for the specified Stream object. (Inherited from HashAlgorithm)
Create()	Obsolete. Creates an instance of the default implementation of a Hash-based Message Authentication Code (HMAC).
Create(String)	Obsolete. Creates an instance of the specified implementation of a Hash-based Message Authentication Code (HMAC).
Dispose()	Releases all resources used by the current instance of the HashAlgorithm class. (Inherited from HashAlgorithm)
Dispose(Boolean)	Releases the unmanaged resources used by the HMAC class when a key change is legitimate and optionally releases the managed resources.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
HashCore(Byte[], Int32, Int32)	When overridden in a derived class, routes data written to the object into the HMAC algorithm for computing the HMAC value.
HashCore(ReadOnlySpan<Byte>)	Routes data written to the object into the HMAC algorithm for computing the HMAC.
HashFinal()	When overridden in a derived class, finalizes the HMAC computation after the last data is processed by the algorithm.
Initialize()	Initializes an instance of the default implementation of 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(Byte[], Int32, Int32, Byte[], Int32)	Computes the hash value for the specified region of the input byte array and copies the specified region of the input byte array to the specified region of the output byte array. (Inherited from HashAlgorithm)
TransformFinalBlock(Byte[], Int32, Int32)	Computes the hash value for the specified region of the specified byte array. (Inherited from HashAlgorithm)
TryComputeHash(ReadOnlySpan<Byte>, Span<Byte>, Int32)	Attempts to compute the hash value for the specified byte array. (Inherited from HashAlgorithm)
TryHashFinal(Span<Byte>, Int32)	Attempts to finalize the HMAC computation after the last data is processed by the HMAC algorithm.

See also

• Cryptographic Services