/*
* Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
/*
* (C) Copyright IBM Corp. 2013
*/
package com.sun.crypto.provider;
import java.util.Arrays;
import java.security.*;
import static com.sun.crypto.provider.AESConstants.AES_BLOCK_SIZE;
/**
* This class represents the GHASH function defined in NIST 800-38D
* under section 6.4. It needs to be constructed w/ a hash subkey, i.e.
* block H. Given input of 128-bit blocks, it will process and output
* a 128-bit block.
*
* <p>This function is used in the implementation of GCM mode.
*
* @since 1.8
*/
final class GHASH {
private static final byte P128 = (byte) 0xe1; //reduction polynomial
private static boolean getBit(byte[] b, int pos) {
int p = pos / 8;
pos %= 8;
int i = (b[p] >>> (7 - pos)) & 1;
return i != 0;
}
private static void shift(byte[] b) {
byte temp, temp2;
temp2 = 0;
for (int i = 0; i < b.length; i++) {
temp = (byte) ((b[i] & 0x01) << 7);
b[i] = (byte) ((b[i] & 0xff) >>> 1);
b[i] = (byte) (b[i] | temp2);
temp2 = temp;
}
}
// Given block X and Y, returns the muliplication of X * Y
private static byte[] blockMult(byte[] x, byte[] y) {
if (x.length != AES_BLOCK_SIZE || y.length != AES_BLOCK_SIZE) {
throw new RuntimeException("illegal input sizes");
}
byte[] z = new byte[AES_BLOCK_SIZE];
byte[] v = y.clone();
// calculate Z1-Z127 and V1-V127
for (int i = 0; i < 127; i++) {
// Zi+1 = Zi if bit i of x is 0
if (getBit(x, i)) {
for (int n = 0; n < z.length; n++) {
z[n] ^= v[n];
}
}
boolean lastBitOfV = getBit(v, 127);
shift(v);
if (lastBitOfV) v[0] ^= P128;
}
// calculate Z128
if (getBit(x, 127)) {
for (int n = 0; n < z.length; n++) {
z[n] ^= v[n];
}
}
return z;
}
// hash subkey H; should not change after the object has been constructed
private final byte[] subkeyH;
// buffer for storing hash
private byte[] state;
// variables for save/restore calls
private byte[] stateSave = null;
/**
* Initializes the cipher in the specified mode with the given key
* and iv.
*
* @param subkeyH the hash subkey
*
* @exception ProviderException if the given key is inappropriate for
* initializing this digest
*/
GHASH(byte[] subkeyH) throws ProviderException {
if ((subkeyH == null) || subkeyH.length != AES_BLOCK_SIZE) {
throw new ProviderException("Internal error");
}
this.subkeyH = subkeyH;
this.state = new byte[AES_BLOCK_SIZE];
}
/**
* Resets the GHASH object to its original state, i.e. blank w/
* the same subkey H. Used after digest() is called and to re-use
* this object for different data w/ the same H.
*/
void reset() {
Arrays.fill(state, (byte) 0);
}
/**
* Save the current snapshot of this GHASH object.
*/
void save() {
stateSave = state.clone();
}
/**
* Restores this object using the saved snapshot.
*/
void restore() {
state = stateSave;
}
private void processBlock(byte[] data, int ofs) {
if (data.length - ofs < AES_BLOCK_SIZE) {
throw new RuntimeException("need complete block");
}
for (int n = 0; n < state.length; n++) {
state[n] ^= data[ofs + n];
}
state = blockMult(state, subkeyH);
}
void update(byte[] in) {
update(in, 0, in.length);
}
void update(byte[] in, int inOfs, int inLen) {
if (inLen - inOfs > in.length) {
throw new RuntimeException("input length out of bound");
}
if (inLen % AES_BLOCK_SIZE != 0) {
throw new RuntimeException("input length unsupported");
}
for (int i = inOfs; i < (inOfs + inLen); i += AES_BLOCK_SIZE) {
processBlock(in, i);
}
}
byte[] digest() {
try {
return state.clone();
} finally {
reset();
}
}
}