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11/17/2011

HashAlgorithm Class

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Represents the base class from which all implementations of cryptographic hash algorithms must derive.

Inheritance Hierarchy

System.Object
  System.Security.Cryptography.HashAlgorithm
    System.Security.Cryptography.KeyedHashAlgorithm
    System.Security.Cryptography.SHA1
    System.Security.Cryptography.SHA256

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class HashAlgorithm _
    Implements ICryptoTransform, IDisposable

[ComVisibleAttribute(true)]
public abstract class HashAlgorithm : ICryptoTransform, 
    IDisposable

The HashAlgorithm type exposes the following members.

Constructors

	Name	Description
	HashAlgorithm	Initializes a new instance of the HashAlgorithm class.

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Properties

	Name	Description
	CanReuseTransform	Gets a value indicating whether the current transform can be reused.
	CanTransformMultipleBlocks	When overridden in a derived class, gets a value indicating whether multiple blocks can be transformed.
	Hash	Gets the value of the computed hash code.
	HashSize	Gets the size, in bits, of the computed hash code.
	InputBlockSize	When overridden in a derived class, gets the input block size.
	OutputBlockSize	When overridden in a derived class, gets the output block size.

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Methods

	Name	Description
	Clear	Releases all resources used by the HashAlgorithm class.
	ComputeHash(array<Byte[])	Computes the hash value for the specified byte array.
	ComputeHash(Stream)	Computes the hash value for the specified Stream object.
	ComputeHash(array<Byte[], Int32, Int32)	Computes the hash value for the specified region of the specified byte array.
	Dispose	Releases the unmanaged resources used by the HashAlgorithm and optionally releases the managed resources.
	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 hash algorithm for computing the hash.
	HashFinal	When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object.
	Initialize	Initializes an implementation of the HashAlgorithm class.
	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.
	TransformFinalBlock	Computes the hash value for the specified region of the specified byte array.

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Fields

	Name	Description
	HashSizeValue	Represents the size, in bits, of the computed hash code.
	HashValue	Represents the value of the computed hash code.
	State	Represents the state of the hash computation.

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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.

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Remarks

Hash functions are fundamental to modern cryptography. These functions map binary strings of an arbitrary length to small binary strings of a fixed length, known as hash values. A cryptographic hash function has the property that it is computationally infeasible to find two distinct inputs that hash to the same value. Hash functions are commonly used with digital signatures and for data integrity.

The hash is used as a unique value of fixed size representing a large amount of data. Hashes of two sets of data should match if the corresponding data also matches. Small changes to the data result in large unpredictable changes in the hash.

Notes to Inheritors

When you inherit from the HashAlgorithm class, you must override the following members: HashCore and HashFinal.

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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