密码学中的DES简化版

package com.hengyunsoft.cryptography.sign.desimpl;

import java.util.Arrays;
import java.util.Random;

import com.hengyunsoft.cryptography.sign.SignReversible;

public class SimpleDesSign implements SignReversible {

//下面这个是秘钥
private byte[] secretKeys = new byte[] {5,62,54,110,26,57,96,41,96,45,12,74,9,63,7,4,120,44}; //56 bit 秘钥
public SimpleDesSign() {
// Random r = new Random();
// r.nextBytes(secretKeys);
}
@Override
public byte[] encrypt(byte[] b) {
if(b.length != {
throw new IllegalArgumentException();
}
Entity[] fs = new Entity[17];
fs[0] = IP(b);
for (int i = 1; i <= 16; i++) {
fs[i] = new Entity();
fs[i].l = fs[i-1].r;
fs[i].r = xor(fs[i-1].l , f(fs[i-1].r,i));
}
return DIP(fs[16]);
}


/**
* 组合
* @param entity
* @return
*/
private byte[] DIP(Entity entity) {
byte[] result = new byte[8];
byte[] l = entity.l;
for (int i = 0; i < 4; i++) {
result[i] = l[i];
}
l = entity.r;
for (int i = 4; i < 8; i++) {
result[i] = l[i-4];
}
return result;
}

private byte[] xor(byte[] l, byte[] f) {
byte[] result = new byte[l.length];
for (int i = 0; i < l.length; i++) {
result[i] = (byte) (l[i] ^ f[i]);
}
return result;
}

private byte[] f(byte[] r, int secretKeyBitIndex) {
secretKeyBitIndex = secretKeyBitIndex*2;
int index = secretKeyBitIndex >> 3;
int startIndex = secretKeyBitIndex & 7;
byte[] secretKey  = new byte[4];
if(startIndex == 0) {
for (int i = index,j=0; j < secretKey.length; i++,j++) {
secretKey[j] = secretKeys[i];
}
} else {
for (int i = index,j=0; j < secretKey.length; i++,j++) {
secretKey[j] = (byte) ((byte)(secretKeys[i] >> startIndex) | (byte)(secretKeys[i+1] << (8-startIndex))) ;
}
}
byte[] result = new byte[4];
for (int i = 0; i < result.length; i++) {
result[i] = (byte) (r[i] ^ secretKey[i]);
}
return result;
}

private byte[] Df(byte[] r, int i) {

return f(r, i);
}

/**
* 密码分组
* @param b
* @return
*/
private Entity IP(byte[] b) {

Entity result = new Entity();
result.l = Arrays.copyOfRange(b, 0, 4);
result.r = Arrays.copyOfRange(b, 4,;
return result;
}

@Override
public byte[] decrypt(byte[] b) {
if(b.length != {
throw new IllegalArgumentException();
}
Entity[] fs = new Entity[17];
fs[16] = IP(b);
for (int i = 16; i >= 1; i--) {
fs[i-1] = new Entity();
fs[i-1].r = fs[i].l;
fs[i-1].l = xor(fs[i].r , Df(fs[i-1].r,i));
}
return DIP(fs[0]);
}

private static class  Entity{
private byte[] l;
private byte[] r;
}

public static void main(String[] args) {
SimpleDesSign s = new SimpleDesSign();
byte[] encode = s.encrypt("12549632".getBytes());
System.out.println(new String(encode));
System.out.println(new String(s.decrypt(encode)));
}
}