iaik.security.md
Class Md2

java.lang.Object
  |
  +--java.security.MessageDigestSpi
        |
        +--java.security.MessageDigest
              |
              +--iaik.security.md.AbstractMessageDigest
                    |
                    +--iaik.security.md.Md2

All Implemented Interfaces:

Cloneable

public class Md2

extends iaik.security.md.AbstractMessageDigest

This class implements the MD2 message digest algorithm.

by Ron Rivestīs MD2 algorithm is described by Burt Kaliski in RFC 1319 (and previously in RFC 1115). It is a secure hash function that takes input of arbitrary length and produces an output of exactly 16 bytes (128 bit).

It is designed for 8 bit machines and therefore does not deliver optimum performance on todays processors with a wordsize of 32 and more bits. Additionally, some weaknesses have been found in the compression function employed by MD2, although the algorithm can still be considered secure because of a checksum that is appended to the data. Nevertheless we recommend using MD5 or even better SHA-1 both for speed and security reasons. Basically MD2 is implemented only to allow certain certificates from RSA Inc. and Verisign to be verified.

An excerpt from the original RFC1319 follows:

 This document describes the MD2 message-digest algorithm. The
 algorithm takes as input a message of arbitrary length and produces
 as output a 128-bit "fingerprint" or "message digest" of the input.
 It is conjectured that it is computationally infeasible to produce
 two messages having the same message digest, or to produce any
 message having a given prespecified target message digest. The MD2
 algorithm is intended for digital signature applications, where a
 large file must be "compressed" in a secure manner before being
 signed with a private (secret) key under a public-key cryptosystem
 such as RSA.
 

This class extends the java.security.MessageDigest class and applications should use one of the getInstance methods presented there to create a MessageDigest-MD2 object. Generally, an application wishing to compute the message digest of some data has to perform three steps:

• First an instance of the desired message digest algorithm has to be created using a proper getInstance method, e.g.:

       MessageDigest md2 = MessageDigest.getInstance("MD2");
       

• Second, the data to be hashed is supplied to the MessageDigest object just created by one or more calls to one of the update methods, e.g:
  

       md2.update(m1);
       md2.update(m2);
       ...
       

• Finally, the hash value can be computed using one of the digest methods:
  

       byte[] hash_value = md2.digest();
       

  
  

There are several ways for combining update and digest methods for computing a message digest. Since this class implements the Cloneable interface, MD2 MessageDigest objects may be used for compute intermediate hashes through cloning (see http://java.sun.com/products/JDK/1.1/docs/guide/security/CryptoSpec.html).

When the hash value successfully has been computed, the MD2 MessageDigest object automatically resets for being able to be supplied with new data to be hashed.

The MD2 algorithm may be combined with a public-key algorithm (e.g. RSA) to be used as digital signature algorithm (see iaik.security.rsa.Md2RSASignature).

Version:

File Revision 28

See Also:

Md2RSASignature, SHA, Md5

Constructor Summary

Md2()
Creates a new MD2 message digest object.

Method Summary

Object	clone() Returns a clone of this Md2 Object.
void	destroyCriticalData()
protected byte[]	engineDigest() b>SPI: Completes the hash computation by performing final operations such as padding.
int	engineGetDigestLength() SPI: Returns the length of the digest in bytes.
void	engineReset() SPI: Resets this MD2 message digest object for being supplied with new data.
protected void	engineUpdate(byte input) SPI: Updates the data to be hashed with the specified byte.
protected void	engineUpdate(byte[] input, int offset, int len) SPI: Updates the data to be hashed with the specified number of bytes, beginning at the specified offset within the given byte array.
protected void	finalize()

Methods inherited from class java.security.MessageDigest

digest, digest, digest, getAlgorithm, getDigestLength, getInstance, getInstance, getProvider, isEqual, reset, toString, update, update, update

Methods inherited from class java.security.MessageDigestSpi

engineDigest

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Md2

public Md2()

Creates a new MD2 message digest object.

Applications do not use this constructor. They shall use

MessageDigest.getInstance("MD2");

for creating a MesssageDigest object.

See Also:

MessageDigest.getInstance(java.lang.String)

Method Detail

clone

public Object clone()

Returns a clone of this Md2 Object.

Overrides:

clone in class iaik.security.md.AbstractMessageDigest

Returns:

a clone of this Md2 Object

engineReset

public void engineReset()

SPI: Resets this MD2 message digest object for being supplied with new data.

This method is called by engineDigest after the actual hash computation has been finished to automatically reset the message digest object for being supplied with new data for starting a new hash computation.

Overrides:

engineReset in class iaik.security.md.AbstractMessageDigest

See Also:

AbstractMessageDigest.engineDigest()

destroyCriticalData

public void destroyCriticalData()

finalize

protected void finalize()

Overrides:

finalize in class Object

engineUpdate

protected final void engineUpdate(byte input)

SPI: Updates the data to be hashed with the specified byte.

Overrides:

engineUpdate in class MessageDigestSpi

Parameters:

input - the byte to be used for updating.

engineUpdate

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

SPI: Updates the data to be hashed with the specified number of bytes, beginning at the specified offset within the given byte array.

Overrides:

engineUpdate in class MessageDigestSpi

Parameters:

input - the byte array holding the data to be used for this update operation.

offset - the offset, indicating the start position within the given byte array.

len - the number of bytes to be obtained from the given byte array, starting at the given position.

engineDigest

protected byte[] engineDigest()

b>SPI: Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset. Resetting is the responsibility of the engine implementor.

Overrides:

engineDigest in class MessageDigestSpi

Returns:

The computed hash value.

See Also:

AbstractMessageDigest.engineReset()

engineGetDigestLength

public int engineGetDigestLength()

SPI: Returns the length of the digest in bytes.

May not be available for applications before JDK versions >= 1.2.x.

Overrides:

engineGetDigestLength in class MessageDigestSpi

Returns:

the length of the digest in bytes.