java.security
Class MessageDigestSpi

java.lang.Object
  extended by java.security.MessageDigestSpi
Direct Known Subclasses:
MessageDigest

public abstract class MessageDigestSpi
extends Object

This is the Service Provider Interface (SPI) for MessageDigest class in java.security. It provides the back end functionality for the MessageDigest class so that it can compute message hashes. The default hashes are SHA-1 and MD5. A message hash takes data of arbitrary length and produces a unique number representing it. Cryptography service providers who want to implement their own message digest hashes need only to subclass this class. The implementation of a Cloneable interface is left to up to the programmer of a subclass.


Constructor Summary
MessageDigestSpi()
          Default constructor of the MessageDigestSpi class
 
Method Summary
 Object clone()
          Returns a clone of this class.
protected abstract  byte[] engineDigest()
          Computes the final digest of the stored bytes and returns them.
protected  int engineDigest(byte[] buf, int offset, int len)
          Computes the final digest of the stored bytes and returns them.
protected  int engineGetDigestLength()
          Returns the length of the digest.
protected abstract  void engineReset()
          Resets the digest engine.
protected abstract  void engineUpdate(byte input)
          Updates the digest with the specified byte.
protected abstract  void engineUpdate(byte[] input, int offset, int len)
          Updates the digest with the specified bytes starting with the offset and proceeding for the specified length.
protected  void engineUpdate(ByteBuffer input)
          Updates this digest with the remaining bytes of a byte buffer.
 
Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

MessageDigestSpi

public MessageDigestSpi()
Default constructor of the MessageDigestSpi class

Method Detail

engineGetDigestLength

protected int engineGetDigestLength()
Returns the length of the digest. It may be overridden by the provider to return the length of the digest. Default is to return 0. It is concrete for backwards compatibility with JDK1.1 message digest classes.

Returns:
Length of Digest in Bytes
Since:
1.2

engineUpdate

protected abstract void engineUpdate(byte input)
Updates the digest with the specified byte.

Parameters:
input - the byte to update digest with

engineUpdate

protected abstract void engineUpdate(byte[] input,
                                     int offset,
                                     int len)
Updates the digest with the specified bytes starting with the offset and proceeding for the specified length.

Parameters:
input - the byte array to update digest with
offset - the offset of the byte to start with
len - the number of the bytes to update with

engineUpdate

protected void engineUpdate(ByteBuffer input)
Updates this digest with the remaining bytes of a byte buffer.

Parameters:
input - The input buffer.
Since:
1.5

engineDigest

protected abstract byte[] engineDigest()
Computes the final digest of the stored bytes and returns them. It performs any necessary padding. The message digest should reset sensitive data after performing the digest.

Returns:
An array of bytes containing the digest

engineDigest

protected int engineDigest(byte[] buf,
                           int offset,
                           int len)
                    throws DigestException
Computes the final digest of the stored bytes and returns them. It performs any necessary padding. The message digest should reset sensitive data after performing the digest. This method is left concrete for backwards compatibility with JDK1.1 message digest classes.

Parameters:
buf - An array of bytes to store the digest
offset - An offset to start storing the digest at
len - The length of the buffer
Returns:
Returns the length of the buffer
Throws:
DigestException
Since:
1.2

engineReset

protected abstract void engineReset()
Resets the digest engine. Reinitializes internal variables and clears sensitive data.


clone

public Object clone()
             throws CloneNotSupportedException
Returns a clone of this class. If cloning is not supported, then by default the class throws a CloneNotSupportedException. The MessageDigestSpi provider implementation has to overload this class in order to be cloneable.

Overrides:
clone in class Object
Returns:
a copy of the Object
Throws:
CloneNotSupportedException - If this Object does not implement Cloneable
See Also:
Cloneable