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package gnu.crypto.mac;
// ----------------------------------------------------------------------------
// $Id: TMMH16.java,v 1.4 2002/11/07 17:17:45 raif Exp $
//
// Copyright (C) 2001, 2002, Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// GNU Crypto 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
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING. If not, write to the
//
// Free Software Foundation Inc.,
// 59 Temple Place - Suite 330,
// Boston, MA 02111-1307
// USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library. Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
// produce an executable, regardless of the license terms of these
// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
// for each linked independent module, the terms and conditions of the
// license of that module. An independent module is a module which is
// not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the
// library, but you are not obligated to do so. If you do not wish to
// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
import gnu.crypto.Registry;
import gnu.crypto.prng.IRandom;
import gnu.crypto.prng.LimitReachedException;
import java.security.InvalidKeyException;
import java.util.Map;
/**
* TMMH is a universal hash function suitable for message
* authentication in the Wegman-Carter paradigm, as in the Stream Cipher
* Security Transform. It is simple, quick, and especially appropriate for
* Digital Signal Processors and other processors with a fast multiply
* operation, though a straightforward implementation requires storage equal in
* length to the largest message to be hashed.
*
* TMMH is a simple hash function which maps a key and a message to a
* hash value. There are two versions of TMMH: TMMH/16 and TMMH/32. TMMH
* can be used as a message authentication code, as described in Section 5 (see
* References).
*
* The key, message, and hash value are all octet strings, and the lengths of
* these quantities are denoted as KEY_LENGTH,
* MESSAGE_LENGTH, and TAG_LENGTH, respectively. The
* values of KEY_LENGTH and TAG_LENGTH
* MUST be fixed for any particular fixed value of the key, and
* must obey the alignment restrictions described below.
*
* The parameter MAX_HASH_LENGTH, which denotes the maximum
* value which MESSAGE_LENGTH may take, is equal to
* KEY_LENGTH - TAG_LENGTH.
*
* References:
*
*
* -
* The Truncated Multi-Modular Hash Function (TMMH), David A. McGrew.
*
*
* @version $Revision: 1.4 $
*/
public class TMMH16 extends BaseMac {
// Constants and variables
// -------------------------------------------------------------------------
public static final String TAG_LENGTH = "gnu.crypto.mac.tmmh.tag.length";
public static final String KEYSTREAM = "gnu.crypto.mac.tmmh.keystream";
public static final String PREFIX = "gnu.crypto.mac.tmmh.prefix";
private static final int P = (1 << 16) + 1; // the TMMH/16 prime
/** caches the result of the correctness test, once executed. */
private static Boolean valid;
private int tagWords = 0; // the tagLength expressed in words
private IRandom keystream = null; // the keystream generator
private byte[] prefix; // mask to use when operating as an authentication f.
private long keyWords; // key words counter
private long msgLength; // in bytes
private long msgWords; // should be = msgLength * WORD_LENGTH
private int[] context; // the tmmh running context; length == TAG_WORDS
private int[] K0; // the first TAG_WORDS words of the keystream
private int[] Ki; // the sliding TAG_WORDS words of the keystream
private int Mi; // current message word being constructed
// Constructor(s)
// -------------------------------------------------------------------------
/** Trivial 0-arguments constructor. */
public TMMH16() {
super(Registry.TMMH16);
}
/**
* Private constructor for cloning purposes.
*
* @param that the instance to clone.
*/
private TMMH16(TMMH16 that) {
this();
this.tagWords = that.tagWords;
this.keystream = (IRandom) that.keystream.clone();
this.keyWords = that.keyWords;
this.msgLength = that.msgLength;
this.msgWords = that.msgWords;
this.context = (int[]) that.context.clone();
this.prefix = (byte[]) that.prefix.clone();
this.K0 = (int[]) that.K0.clone();
this.Ki = (int[]) that.Ki.clone();
this.Mi = that.Mi;
}
// Class methods
// -------------------------------------------------------------------------
// Instance methods
// -------------------------------------------------------------------------
// java.lang.Cloneable interface implementation ----------------------------
public Object clone() {
return (new TMMH16(this));
}
// gnu.crypto.mac.IMac interface implementation ----------------------------
public int macSize() {
return tagWords * 2;
}
public void init(Map attributes)
throws InvalidKeyException, IllegalStateException {
int wantTagLength = 0;
Integer tagLength = (Integer) attributes.get(TAG_LENGTH); // get tag length
if (tagLength == null) {
if (tagWords == 0) { // was never set
throw new IllegalArgumentException(TAG_LENGTH);
} // else re-use
} else { // check if positive and is divisible by WORD_LENGTH
wantTagLength = tagLength.intValue();
if (wantTagLength < 2 || (wantTagLength % 2 != 0)) {
throw new IllegalArgumentException(TAG_LENGTH);
} else if (wantTagLength > (512/8)) { // 512-bits is our maximum
throw new IllegalArgumentException(TAG_LENGTH);
}
tagWords = wantTagLength / 2; // init local vars
K0 = new int[tagWords];
Ki = new int[tagWords];
context = new int[tagWords];
}
prefix = (byte[]) attributes.get(PREFIX);
if (prefix == null) { // default to all-zeroes
prefix = new byte[tagWords * 2];
} else { // ensure it's as long as it should
if (prefix.length != tagWords * 2) {
throw new IllegalArgumentException(PREFIX);
}
}
IRandom prng = (IRandom) attributes.get(KEYSTREAM); // get keystream
if (prng == null) {
if (keystream == null) {
throw new IllegalArgumentException(KEYSTREAM);
} // else reuse
} else {
keystream = prng;
}
reset(); // reset context variables
for (int i = 0; i < tagWords; i++) { // init starting key words
Ki[i] = K0[i] = getNextKeyWord(keystream);
}
}
// The words of the key are denoted as K[1], K[2], ..., K[KEY_WORDS], and the
// words of the message (after zero padding, if needed) are denoted as M[1],
// M[2], ..., M[MSG_WORDS], where MSG_WORDS is the smallest number such that
// 2 * MSG_WORDS is at least MESSAGE_LENGTH, and KEY_WORDS is KEY_LENGTH / 2.
//
// If MESSAGE_LENGTH is greater than MAX_HASH_LENGTH, then the value of
// TMMH/16 is undefined. Implementations MUST indicate an error if asked to
// hash a message with such a length. Otherwise, the hash value is defined
// to be the length TAG_WORDS sequence of words in which the j-th word in the
// sequence is defined as
//
// [ [ K[j] * MESSAGE_LENGTH +32 K[j+1] * M[1] +32 K[j+2] * M[2]
// +32 ... K[j+MSG_WORDS] * M[MSG_WORDS] ] modulo p ] modulo 2^16
//
// where j ranges from 1 to TAG_WORDS.
public void update(byte b) {
this.update(b, keystream);
}
public void update(byte[] b, int offset, int len) {
for (int i = 0; i < len; i++) {
this.update(b[offset + i], keystream);
}
}
// For TMMH/16, KEY_LENGTH and TAG_LENGTH MUST be a multiple of two. The key,
// message, and hash value are treated as a sequence of unsigned sixteen bit
// integers in network byte order. (In this section, we call such an integer
// a word.) If MESSAGE_LENGTH is odd, then a zero byte is appended to the
// message to align it on a word boundary, though this process does not
// change the value of MESSAGE_LENGTH.
//
// ... Otherwise, the hash value is defined to be the length TAG_WORDS
// sequence of words in which the j-th word in the sequence is defined as
//
// [ [ K[j] * MESSAGE_LENGTH +32 K[j+1] * M[1] +32 K[j+2] * M[2]
// +32 ... K[j+MSG_WORDS] * M[MSG_WORDS] ] modulo p ] modulo 2^16
//
// where j ranges from 1 to TAG_WORDS.
//
// Here, TAG_WORDS is equal to TAG_LENGTH / 2, and p is equal to 2^16 + 1.
// The symbol * denotes multiplication and the symbol +32 denotes addition
// modulo 2^32.
public byte[] digest() {
return this.digest(keystream);
}
public void reset() {
msgLength = msgWords = keyWords = 0L;
Mi = 0;
for (int i = 0; i < tagWords; i++) {
context[i] = 0;
}
}
public boolean selfTest() {
if (valid == null) {
// TODO: compute and test equality with one known vector
valid = Boolean.TRUE;
}
return valid.booleanValue();
}
// own methods -------------------------------------------------------------
/**
* Similar to the same method with one argument, but uses the designated
* random number generator to compute needed keying material.
*
* @param b the byte to process.
* @param prng the source of randomness to use.
*/
public void update(byte b, IRandom prng) {
Mi <<= 8; // update message buffer
Mi |= b & 0xFF;
msgLength++; // update message length (bytes)
if (msgLength % 2 == 0) { // got a full word
msgWords++; // update message words counter
System.arraycopy(Ki, 1, Ki, 0, tagWords-1); // 1. shift Ki up by 1
Ki[tagWords-1] = getNextKeyWord(prng); // 2. fill last box of Ki
long t; // temp var to allow working in modulo 2^32
for (int i = 0; i < tagWords; i++) { // 3. update context
t = context[i] & 0xFFFFFFFFL;
t += Ki[i] * Mi;
context[i] = (int) t;
}
Mi = 0; // reset message buffer
}
}
/**
* Similar to the same method with three arguments, but uses the
* designated random number generator to compute needed keying material.
*
* @param b the byte array to process.
* @param offset the starting offset in b to start considering
* the bytes to process.
* @param len the number of bytes in b starting from
* offset to process.
* @param prng the source of randomness to use.
*/
public void update(byte[] b, int offset, int len, IRandom prng) {
for (int i = 0; i < len; i++) {
this.update(b[offset + i], prng);
}
}
/**
* Similar to the same method with no arguments, but uses the designated
* random number generator to compute needed keying material.
*
* @param prng the source of randomness to use.
* @return the final result of the algorithm.
*/
public byte[] digest(IRandom prng) {
doFinalRound(prng);
byte[] result = new byte[tagWords * 2];
for (int i = 0, j = 0; i < tagWords; i++) {
result[j] = (byte)((context[i] >>> 8) ^ prefix[j]);
j++;
result[j] = (byte)( context[i] ^ prefix[j]);
j++;
}
reset();
return result;
}
private int getNextKeyWord(IRandom prng) {
int result = 0;
try {
result = (prng.nextByte() & 0xFF) << 8 | (prng.nextByte() & 0xFF);
} catch (LimitReachedException x) {
throw new RuntimeException(String.valueOf(x));
}
keyWords++; // update key words counter
return result;
}
private void doFinalRound(IRandom prng) {
long limit = msgLength; // formula works on real message length
while (msgLength % 2 != 0) {
update((byte) 0x00, prng);
}
long t;
for (int i = 0; i < tagWords; i++) {
t = context[i] & 0xFFFFFFFFL;
t += K0[i] * limit;
t %= P;
context[i] = (int) t;
}
}
}