DES加密算法中的IP置换算法

// DES.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>

//////////////////////////////////////////////////////////////////////////
// DES加密、解密算法
// 作者：liujichao

// DES算法：64位明文（不足需补位） + 56位密钥（8个校验位) --> 64位密文

// 定义32位无符号类型
typedef unsigned long DWORD;

// DES 64位块
typedef struct tagBLOCK
{
    DWORD dwLeft32;        // 高32位
    DWORD dwRight32;    // 低32位
}BLOCK, *LPBLOCK;

namespace
{    
    // 正向置换表
    int DES_IP[] = 
    {
        58, 50, 42, 34, 26, 18, 10, 2, 
        60, 52, 44, 36, 28, 20, 12, 4,
        62, 54, 46, 38, 30, 22, 14, 6,
        64, 56, 48, 40, 32, 24, 16, 8,
        57, 49, 41, 33, 25, 17, 9, 1,
        59, 51, 43, 35, 27, 19, 11, 3,
        61, 53, 45, 37, 29, 21, 13, 5,
        63, 55, 47, 39, 31, 23, 15, 7
    };
    
    // 逆向置换表
    int DES_NIP[] = 
    {
        40, 8, 48, 16, 56, 24, 64, 32,
        39, 7, 47, 15, 55, 23, 63, 31,
        38, 6, 46, 14, 54, 22, 62, 30,
        37, 5, 45, 13, 53, 21, 61, 29,
        36, 4, 44, 12, 52, 20, 60, 28,
        35, 3, 43, 11, 51, 19, 59, 27,
        34, 2, 42, 10, 50, 18, 58, 26,
        33, 1, 41, 9, 49, 17, 57, 25
    };
}

// DES IP置换算法
void DesIpTransform(LPBLOCK lpBlock, bool bDirection = true)
{
    // 缓冲临时置换数据
    BLOCK buffer;
    memset(&buffer, 0, sizeof(BLOCK));
    
    // 指定置换表
    int* ip = bDirection ? DES_IP : DES_NIP;
    
    // 比特位置换过程
    for(int i = 0; i < 64; ++i)
    {
        // 防止边界外非法读、写操作
        //assert((table[i] >= 0) && (table[i] < 64));
        
        // 低32位置换
        if(i <= 31)
        {
            if(ip[i] > 32)
            {
                buffer.dwLeft32 |= ( (lpBlock->dwRight32 >> (64 - ip[i]) ) & 0x01) << (31 - i);
            }
            else
            {
                buffer.dwLeft32 |= ( (lpBlock->dwLeft32 >> (32 - ip[i]) ) & 1) << (31 - i);
            }
        }
        // 高32位置换
        else
        {
            if (ip[i] < 32)
            {
                buffer.dwRight32 |= ( (lpBlock->dwLeft32 >> (32 - ip[i]) ) & 1) << (31 - i);
            }
            else
            {
                buffer.dwRight32 |= ( (lpBlock->dwRight32 >> (64 - ip[i]) ) & 1) << (31 - i);
            }
        }
    }
    
    lpBlock->dwLeft32 = buffer.dwLeft32;
    lpBlock->dwRight32 = buffer.dwRight32;
}

int main(int argc, char* argv[])
{
    BLOCK block = {0x01, 0x02};
    DesIpTransform(&block, true);

    DesIpTransform(&block, false);

    return 0;
}