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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class MessageDigestSpi - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.security
Class MessageDigestSpi

java.lang.Object
  |
  +--java.security.MessageDigestSpi

Direct Known Subclasses:

MessageDigest

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public abstract class MessageDigestSpi

extends Object

This class defines the Service Provider Interface (SPI) for the MessageDigest class, which provides the functionality of a message digest algorithm, such as MD5 or SHA. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value.

All the abstract methods in this class must be implemented by a cryptographic service provider who wishes to supply the implementation of a particular message digest algorithm.

Implementations are free to implement the Cloneable interface.

See Also:

MessageDigest

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Constructor Summary

MessageDigestSpi()

 

Method Summary
Object	clone()           Returns a clone if the implementation is cloneable.
protected abstract  byte[]	engineDigest()           Completes the hash computation by performing final operations such as padding.
protected  int	engineDigest(byte[] buf, int offset, int len)           Completes the hash computation by performing final operations such as padding.
protected  int	engineGetDigestLength()           Returns the digest length in bytes.
protected abstract  void	engineReset()           Resets the digest for further use.
protected abstract  void	engineUpdate(byte input)           Updates the digest using the specified byte.
protected abstract  void	engineUpdate(byte[] input, int offset, int len)           Updates the digest using the specified array of bytes, starting at the specified offset.

 

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Constructor Detail

MessageDigestSpi

public MessageDigestSpi()

Method Detail

engineGetDigestLength

protected int engineGetDigestLength()

Returns the digest length in bytes.

This concrete method has been added to this previously-defined abstract class. (For backwards compatibility, it cannot be abstract.)

The default behavior is to return 0.

This method may be overridden by a provider to return the digest length.

Returns:

the digest length in bytes.

Since:

JDK1.2

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engineUpdate

protected abstract void engineUpdate(byte input)

Updates the digest using the specified byte.

Parameters:

input - the byte to use for the update.

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engineUpdate

protected abstract void engineUpdate(byte[] input,
                                     int offset,
                                     int len)

Updates the digest using the specified array of bytes, starting at the specified offset.

Parameters:

input - the array of bytes to use for the update.

offset - the offset to start from in the array of bytes.

len - the number of bytes to use, starting at offset.

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engineDigest

protected abstract byte[] engineDigest()

Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor.

Returns:

the array of bytes for the resulting hash value.

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engineDigest

protected int engineDigest(byte[] buf,
                           int offset,
                           int len)
                    throws DigestException

Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor. This method should be abstract, but we leave it concrete for binary compatibility. Knowledgeable providers should override this method.

Parameters:

buf - the output buffer in which to store the digest

offset - offset to start from in the output buffer

len - number of bytes within buf allotted for the digest. Both this default implementation and the SUN provider do not return partial digests. The presence of this parameter is solely for consistency in our API's. If the value of this parameter is less than the actual digest length, the method will throw a DigestException. This parameter is ignored if its value is greater than or equal to the actual digest length.

Returns:

the length of the digest stored in the output buffer.

Throws:

DigestException - if an error occurs.

Since:

JDK1.2

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engineReset

protected abstract void engineReset()

Resets the digest for further use.

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clone

public Object clone()
             throws CloneNotSupportedException

Returns a clone if the implementation is cloneable.

Overrides:

clone in class Object

Returns:

a clone if the implementation is cloneable.

Throws:

CloneNotSupportedException - if this is called on an implementation that does not support Cloneable.

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