com.twmacinta.util
Class MD5

java.lang.Object
  com.twmacinta.util.MD5

public class MD5
extends java.lang.Object

Fast implementation of RSA's MD5 hash generator in Java JDK Beta-2 or higher.

Originally written by Santeri Paavolainen, Helsinki Finland 1996.
(c) Santeri Paavolainen, Helsinki Finland 1996
Many changes Copyright (c) 2002 - 2010 Timothy W Macinta

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details.

You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

See http://www.twmacinta.com/myjava/fast_md5.php for more information on this file and the related files.

This was originally a rather straight re-implementation of the reference implementation given in RFC1321 by RSA. It passes the MD5 test suite as defined in RFC1321.

Many optimizations made by Timothy W Macinta. Reduced time to checksum a test file in Java alone to roughly half the time taken compared with java.security.MessageDigest (within an intepretter). Also added an optional native method to reduce the time even further. See http://www.twmacinta.com/myjava/fast_md5.php for further information on the time improvements achieved.

Some bug fixes also made by Timothy W Macinta.

Please note: I (Timothy Macinta) have put this code in the com.twmacinta.util package only because it came without a package. I was not the the original author of the code, although I did optimize it (substantially) and fix some bugs.

This Java class has been derived from the RSA Data Security, Inc. MD5 Message-Digest Algorithm and its reference implementation.

This class will attempt to use a native method to quickly compute checksums when the appropriate native library is available. On Linux, this library should be named "MD5.so" and on Windows it should be named "MD5.dll". The code will attempt to locate the library in the following locations in the order given:

1. The path specified by the system property "com.twmacinta.util.MD5.NATIVE_LIB_FILE" (be sure to include "MD5.so", "MD5.dll", or "MD5.jnilib" as appropriate at the end of the path).
2. A platform specific directory beneath the "lib/arch/" directory. For example, On Windows for 32 bit x86 architectures, this is "lib/arch/win32_x86/".
3. Within the "lib/" directory.
4. Within the current directory.

If the library is not found, the code will fall back to the default (slower) Java code.

As a side effect of having the code search for the native library, SecurityExceptions might be thrown on JVMs that have a restrictive SecurityManager. The initialization code attempts to silently discard these exceptions and continue, but many SecurityManagers will attempt to notify the user directly of all SecurityExceptions thrown. Consequently, the code has provisions for skipping the search for the native library. Any of these provisions may be used to skip the search as long as they are performed before the first instance of a com.twmacinta.util.MD5 object is constructed (note that the convenience stream objects will implicitly create an MD5 object).

The first option is to set the system property "com.twmacinta.util.MD5.NO_NATIVE_LIB" to "true" or "1". Unfortunately, SecurityManagers may also choose to disallow system property setting, so this won't be of use in all cases.

The second option is to call com.twmacinta.util.MD5.initNativeLibrary(true) before any MD5 objects are constructed.

Author:

Santeri Paavolainen , Timothy W Macinta (twm@alum.mit.edu) (optimizations and bug fixes)

Constructor Summary

MD5()
Class constructor

MD5(java.lang.Object ob)
Initialize class, and update hash with ob.toString()

Method Summary

java.lang.String	asHex() Returns 32-character hex representation of this objects hash
static java.lang.String	asHex(byte[] hash) Turns array of bytes into string representing each byte as unsigned hex number.
byte[]	Final() Returns array of bytes (16 bytes) representing hash as of the current state of this object.
static byte[]	getHash(java.io.File f) Calculates and returns the hash of the contents of the given file.
static boolean	hashesEqual(byte[] hash1, byte[] hash2)
void	Init() Initialize MD5 internal state (object can be reused just by calling Init() after every Final()
static boolean	initNativeLibrary() Convenience method for initNativeLibrary(false).
static boolean	initNativeLibrary(boolean disallow_lib_loading) Attempts to initialize native library support.
void	Update(byte b) Updates hash with a single byte
void	Update(byte[] buffer) Updates hash with given array of bytes
void	Update(byte[] buffer, int length)
void	Update(byte[] buffer, int offset, int length) Plain update, updates this object
void	Update(int i) Update buffer with a single integer (only & 0xff part is used, as a byte)
void	Update(com.twmacinta.util.MD5State stat, byte[] buffer, int offset, int length) Updates hash with the bytebuffer given (using at maximum length bytes from that buffer)
void	Update(java.lang.String s) Update buffer with given string.
void	Update(java.lang.String s, java.lang.String charset_name) Update buffer with given string using the given encoding.

Methods inherited from class java.lang.Object

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

Constructor Detail

MD5

public MD5()

Class constructor

MD5

public MD5(java.lang.Object ob)

Initialize class, and update hash with ob.toString()

Parameters:

ob - Object, ob.toString() is used to update hash after initialization

Method Detail

Init

public void Init()

Initialize MD5 internal state (object can be reused just by calling Init() after every Final()

Update

public void Update(com.twmacinta.util.MD5State stat,
                   byte[] buffer,
                   int offset,
                   int length)

Updates hash with the bytebuffer given (using at maximum length bytes from that buffer)

Parameters:

stat - Which state is updated

buffer - Array of bytes to be hashed

offset - Offset to buffer array

length - Use at maximum `length' bytes (absolute maximum is buffer.length)

Update

public void Update(byte[] buffer,
                   int offset,
                   int length)

Plain update, updates this object

Update

public void Update(byte[] buffer,
                   int length)

Update

public void Update(byte[] buffer)

Updates hash with given array of bytes

Parameters:

buffer - Array of bytes to use for updating the hash

Update

public void Update(byte b)

Updates hash with a single byte

Parameters:

b - Single byte to update the hash

Update

public void Update(java.lang.String s)

Update buffer with given string. Note that because the version of the s.getBytes() method without parameters is used to convert the string to a byte array, the results of this method may be different on different platforms. The s.getBytes() method converts the string into a byte array using the current platform's default character set and may therefore have different results on platforms with different default character sets. If a version that works consistently across platforms with different default character sets is desired, use the overloaded version of the Update() method which takes a string and a character encoding.

Parameters:

s - String to be update to hash (is used as s.getBytes())

Update

public void Update(java.lang.String s,
                   java.lang.String charset_name)
            throws java.io.UnsupportedEncodingException

Update buffer with given string using the given encoding. If the given encoding is null, the encoding "ISO8859_1" is used.

Parameters:

s - String to be update to hash (is used as s.getBytes(charset_name))

charset_name - The character set to use to convert s to a byte array, or null if the "ISO8859_1" character set is desired.

Throws:

java.io.UnsupportedEncodingException - If the named charset is not supported.

Update

public void Update(int i)

Update buffer with a single integer (only & 0xff part is used, as a byte)

Parameters:

i - Integer value, which is then converted to byte as i & 0xff

Final

public byte[] Final()

Returns array of bytes (16 bytes) representing hash as of the current state of this object. Note: getting a hash does not invalidate the hash object, it only creates a copy of the real state which is finalized.

Returns:

Array of 16 bytes, the hash of all updated bytes

asHex

public static java.lang.String asHex(byte[] hash)

Turns array of bytes into string representing each byte as unsigned hex number.

Parameters:

hash - Array of bytes to convert to hex-string

Returns:

Generated hex string

asHex

public java.lang.String asHex()

Returns 32-character hex representation of this objects hash

Returns:

String of this object's hash

initNativeLibrary

public static final boolean initNativeLibrary()

Convenience method for initNativeLibrary(false).

initNativeLibrary

public static final boolean initNativeLibrary(boolean disallow_lib_loading)

Attempts to initialize native library support. If 'disallow_lib_loading' is true, will indicate that the native library should not be loaded now or in the future. If native library support has been previously loaded or disabled, this method has no effect.

Returns:

true iff native library support has been loaded

getHash

public static byte[] getHash(java.io.File f)
                      throws java.io.IOException

Calculates and returns the hash of the contents of the given file.

Throws:

java.io.IOException

hashesEqual

public static boolean hashesEqual(byte[] hash1,
                                  byte[] hash2)

Returns:

true iff the first 16 bytes of both hash1 and hash2 are equal; both hash1 and hash2 are null; or either hash array is less than 16 bytes in length and their lengths and all of their bytes are equal.