Java example source code file (GHASH.java)

This example Java source code file (GHASH.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

aes_block_size, ghash, internal, p128, providerexception, runtimeexception, security, util

The GHASH.java Java example source code

/*
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
/*
 * (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();
        }
    }
}