org.verapdf.tools.RC4Encryption Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of parser Show documentation
veraPDF tools for parsing, modifying and creating PDF documents.
There is a newer version: 1.26.1
/**
 * This file is part of veraPDF Parser, a module of the veraPDF project.
 * Copyright (c) 2015, veraPDF Consortium 
 * All rights reserved.
 *
 * veraPDF Parser is free software: you can redistribute it and/or modify
 * it under the terms of either:
 *
 * The GNU General public license GPLv3+.
 * You should have received a copy of the GNU General Public License
 * along with veraPDF Parser as the LICENSE.GPL file in the root of the source
 * tree.  If not, see http://www.gnu.org/licenses/ or
 * https://www.gnu.org/licenses/gpl-3.0.en.html.
 *
 * The Mozilla Public License MPLv2+.
 * You should have received a copy of the Mozilla Public License along with
 * veraPDF Parser as the LICENSE.MPL file in the root of the source tree.
 * If a copy of the MPL was not distributed with this file, you can obtain one at
 * http://mozilla.org/MPL/2.0/.
 */
package org.verapdf.tools;

/**
 * Implements RC4 encryption algorithm.
 *
 * @author Sergey Shemyakov
 */
public class RC4Encryption {

    private int[] s = new int[256];
    private int[] key;
    private int i;
    private int j;

    /**
     * Constructor from encryption key.
     *
     * @param key is encryption key.
     */
    public RC4Encryption(byte[] key) {
        this.key = new int[key.length];
        arraysCopy(key, this.key);
        this.i = 0;
        this.j = 0;
        keySchedulingAlgorithm();
    }

    /**
     * Encrypts or decrypts passed data with use of current inner state of
     * encryptor.
     *
     * @param data is data to process.
     * @return processed data.
     */
    public byte[] process(byte[] data) {
        return process(data, 0, data.length);
    }

    /**
     * Encrypts or decrypts passed data with use of current inner state of
     * encryptor.
     *
     * @param data   is data to process.
     * @param offset is offset of beginning of data to process.
     * @param size   is amount of bytes to process.
     * @return processed data.
     */
    public byte[] process(byte[] data, int offset, int size) {
        if (size >= 0 && data.length >= offset) {
            int actualSize = Math.min(size, data.length - offset);
            byte[] res = new byte[actualSize];
            for (int k = offset; k < actualSize; k++) {
                res[k] = (byte) (data[k] ^ getNextPseudoRandomByte());
            }
            return res;
        } else {
            return new byte[]{};
        }
    }

    /**
     * Resets inner state of encryptor to default.
     */
    public void reset() {
        this.i = 0;
        this.j = 0;
        keySchedulingAlgorithm();
    }

    private void keySchedulingAlgorithm() {
        for (int i = 0; i < 256; i++) {
            s[i] = i;
        }
        int j = 0;
        for (int i = 0; i < 256; i++) {
            j = (j + s[i] + key[i % key.length]) % 256;
            swapSElements(i, j);
        }
    }

    private byte getNextPseudoRandomByte() {
        i = (i + 1) % 256;
        j = (j + s[i]) % 256;
        swapSElements(i, j);
        return (byte) s[(s[i] + s[j]) % 256];
    }

    private void swapSElements(int i, int j) {
        int tmp;
        tmp = s[i];
        s[i] = s[j];
        s[j] = tmp;
    }

    private static void arraysCopy(byte[] src, int[] dst) {
        for (int i = 0; i < src.length; i++) {
            dst[i] = src[i] & 0xFF;
        }
    }
}