content: /*
  * Copyright 2010 Srikanth Reddy Lingala  
  * 
  * Licensed 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 
  * 
  * https://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 net.lingala.zip4j.crypto.engine;
  
  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;
          }
      }
  	
  	public ZipCryptoEngine() {
  	}
  	
  	public void initKeys(char[] password) {
          keys[0] = 305419896;
          keys[1] = 591751049;
          keys[2] = 878082192;
          for (int i = 0; i < password.length; i++) {
              updateKeys((byte) (password[i] & 0xff));
          }
      }
  	
  	public void updateKeys(byte charAt) {
          keys[0] = crc32(keys[0], charAt);
          keys[1] += keys[0] & 0xff;
          keys[1] = keys[1] * 134775813 + 1;
          keys[2] = crc32(keys[2], (byte) (keys[1] >> 24));
      }
  	
  	private int crc32(int oldCrc, byte charAt) {
      	return ((oldCrc >>> 8) ^ CRC_TABLE[(oldCrc ^ charAt) & 0xff]);
      }
  	
  	public byte decryptByte() {
          int temp = keys[2] | 2;
          return (byte) ((temp * (temp ^ 1)) >>> 8);
      }
  }
  