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Java utility collections, development by Nervousync Studio (NSYC)

There is a newer version: 1.2.1

/*
 * Licensed to the Nervousync Studio (NSYC) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.nervousync.zip.engine;

/**
 * Standard Crypto Engine
 *
 * @author Steven Wee	[email protected]
 * @version $Revision : 1.0 $ $Date: Nov 29, 2017 4:58:52 PM $
 */
public class ZipCryptoEngine {

	private final int[] keys = new int[3];
	private static final int[] CRC_TABLE = new int[256];
	
	static {
		for (int i = 0 ; i < 256 ; i++) {
			int r = i;
			for (int j = 0 ; j < 8 ; j++) {
				if ((r & 1) == 1) {
					r = (r >>> 1) ^ 0xedb88320;
				} else {
					r >>>= 1;
				}
			}
			CRC_TABLE[i] = r;
		}
	}

	/**
	 * Instantiates a new Zip crypto engine.
	 */
	public ZipCryptoEngine() {
	}

	/**
	 * Init keys.
	 *
	 * @param password the password
	 */
	public void initKeys(char[] password) {
		this.keys[0] = 305419896;
		this.keys[1] = 591751049;
		this.keys[2] = 878082192;
		
		for (char ch : password) {
			this.updateKeys((byte)(ch & 0xFF));
		}
	}

	/**
	 * Update keys.
	 *
	 * @param b the b
	 */
	public void updateKeys(byte b) {
		this.keys[0] = crc32(this.keys[0], b);
		this.keys[1] += this.keys[0] & 0xff;
		this.keys[1] = this.keys[1] * 134775813 + 1;
		this.keys[2] = crc32(this.keys[2], (byte)(this.keys[1] >> 24));
	}

	/**
	 * Decrypt byte.
	 *
	 * @return the byte
	 */
	public byte decryptByte() {
		int temp = this.keys[2] | 2;
		return (byte)((temp * (temp ^ 1)) >>> 8);
	}
	
	private static int crc32(int currentCrc, byte b) {
		return ((currentCrc >>> 8) ^ CRC_TABLE[(currentCrc ^ b) & 0xFF]);
	}
}