Xtea.java

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/*
 * Gridarta MMORPG map editor for Crossfire, Daimonin and similar games.
 * Copyright (C) 2000-2015 The Gridarta Developers.
 *
 * This program 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 of the License, or
 * (at your option) any later version.
 *
 * This program 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; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package net.sf.gridarta.utils;

import org.jetbrains.annotations.NotNull;

public class Xtea {

    private static final int NUM_ROUNDS = 32;

    private static final int DELTA = 0x9E3779B9;

    @NotNull
    private final int[] k = new int[4];

    public Xtea(@NotNull final byte[] key) {
        if (key.length != 16) {
            throw new IllegalArgumentException("invalid key length");
        }

        k[0] = getInt(key, 0);
        k[1] = getInt(key, 4);
        k[2] = getInt(key, 8);
        k[3] = getInt(key, 12);
    }

    public void encrypt(@NotNull final byte[] plaintext, @NotNull final byte[] ciphertext) {
        if (plaintext.length != 8) {
            throw new IllegalArgumentException();
        }
        if (ciphertext.length != 8) {
            throw new IllegalArgumentException();
        }
        int v0 = getInt(plaintext, 0);
        int v1 = getInt(plaintext, 4);
        int sum = 0;
        for (int i = 0; i < NUM_ROUNDS; i++) {
            v0 += (((v1 << 4) ^ (v1 >>> 5)) + v1) ^ (sum + k[sum & 3]);
            sum += DELTA;
            v1 += (((v0 << 4) ^ (v0 >>> 5)) + v0) ^ (sum + k[(sum >>> 11) & 3]);
        }
        putInt(v0, ciphertext, 0);
        putInt(v1, ciphertext, 4);
    }

    public void decrypt(@NotNull final byte[] ciphertext, @NotNull final byte[] plaintext) {
        if (ciphertext.length != 8) {
            throw new IllegalArgumentException();
        }
        if (plaintext.length != 8) {
            throw new IllegalArgumentException();
        }
        int v0 = getInt(ciphertext, 0);
        int v1 = getInt(ciphertext, 4);
        //noinspection NumericOverflow
        int sum = DELTA * NUM_ROUNDS;
        for (int i = 0; i < NUM_ROUNDS; i++) {
            v1 -= (((v0 << 4) ^ (v0 >>> 5)) + v0) ^ (sum + k[(sum >>> 11) & 3]);
            sum -= DELTA;
            v0 -= (((v1 << 4) ^ (v1 >>> 5)) + v1) ^ (sum + k[sum & 3]);
        }
        putInt(v0, plaintext, 0);
        putInt(v1, plaintext, 4);
    }

    private static int getInt(@NotNull final byte[] data, final int offset) {
        return ((data[offset + 3] & 255) << 24) | ((data[offset + 2] & 255) << 16) | ((data[offset + 1] & 255) << 8) | data[offset] & 255;
    }

    private static void putInt(final int value, @NotNull final byte[] data, final int offset) {
        data[offset + 3] = (byte) (value >>> 24);
        data[offset + 2] = (byte) (value >>> 16);
        data[offset + 1] = (byte) (value >>> 8);
        data[offset] = (byte) value;
    }

}