net.lingala.zip4j.crypto.engine.ZipCryptoEngine Maven / Gradle / Ivy
/*
* 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
*
* 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 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);
}
}