【DES密码编写】
1. Equipment
（1） operating system version ：WIN 10
（2） CPU instruction set: x 64
（3） software ：Visual Studio 2019
2. process
Problem background analysis
DES密码编写
要编写DES密码，先熟悉DES原理，其基本流程就是先将明文分成64bit的分组，然后将64bit二进制码输入到密码器中，密码器对输入的64位码首先进行初始置换，然后在64bit主密钥产生的16个子密钥控制下进行16 轮乘积变换，接着再进行逆置换就得到64位已加密的密文。DES的流程图如下：
其中DES算法明文分组长为64bit，加密后得到64bit密文，输入初始种子密钥为64bit，第8、16、24、32、40、48、56、64为奇偶校验位，实际的密钥长为56bit。DES加密过程由三个阶段来完成：
- 初始置换IP，用于重排明文分组的64bit数据。经过初始置换，64位的输入得到了两个32位的输出。
- 相同结构的16轮迭代，每轮中都有置换和代换运算，第16轮变换的输出分为左、右两半，并交换次序。
- 逆初始置换IP-1（为IP的逆）后，产生64bit的密文。
按照此思路，编写DES算法。
Solution
code：
#include <string.h>
#include <stdio.h>
#include <iostream>
#pragma warning(disable:4996)
using namespace std;
/*
* @Author:timerring
* @Date: 2021-11-01 19:17:32
* @LastEditTime: 2021-11-05 20:34:13
* @FilePath:c:\Users\timerring\DES.cpp
*/
class DES {
//构造DES类
public:
~DES() {} //定义析构函数
void set_key(const unsigned char*); //密钥扩展
void en_ctransform(const unsigned char*, unsigned char*); //加密变换
void de_ctransform(const unsigned char*, unsigned char*); //解密变换
private:
bool enckey[16][48];//存放加密的子密钥
bool deckey[16][48];//存放解密的子密钥
const static unsigned char IP_Table[64];
//初置换
const static unsigned char IPR_Table[64];
//逆置换
const static unsigned char E_Table[48];
//E表
const static unsigned char P_Table[32];
//置换选择
const static unsigned char PC1_Table[56];
//置换选择1
const static unsigned char PC2_Table[48];
//置换选择2
const static unsigned char LOOP_Table[16];
//密钥位移（左移次数）
const static unsigned char S_Box[8][4][16];
// S盒
};
const unsigned char DES::IP_Table[64] = {
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
};
// 初置换
const unsigned char DES::IPR_Table[64] = {
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
};
// 逆初始置换
const unsigned char DES::E_Table[48] = {
32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9,
8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17,
16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25,
24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1
};
// E表
const unsigned char DES::P_Table[32] = {
16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10,
2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25
};
// 置换选择
const unsigned char DES::PC1_Table[56] = {
57, 49, 41, 33, 25, 17, 9, 1, 58, 50, 42, 34, 26, 18,
10, 2, 59, 51, 43, 35, 27, 19, 11, 3, 60, 52, 44, 36,
63, 55, 47, 39, 31, 23, 15, 7, 62, 54, 46, 38, 30, 22,
14, 6, 61, 53, 45, 37, 29, 21, 13, 5, 28, 20, 12, 4
};
//置换选择1
const unsigned char DES::PC2_Table[48] = {
14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10,
23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2,
41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48,
44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32
};
//置换选择2
const unsigned char DES::LOOP_Table[16] = {
1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1
};
// 密钥位移（左移次数）
const unsigned char DES::S_Box[8][4][16] = {
//8个S盒 ，每个盒为4行16列
// 定义S1盒
14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7,
0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8,
4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0,
15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13,
// 定义S2盒
15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10,
3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5,
0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15,
13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9,
// 定义S3盒
10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,
13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,
13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7,
1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12,
// 定义S4盒
7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15,
13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9,
10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,
3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14,
// 定义S5盒
2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9,
14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6,
4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14,
11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3,
// 定义S6盒
12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,
10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,
9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,
4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13,
// 定义S7盒
4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1,
13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6,
1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2,
6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12,
// 定义S8盒
13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7,
1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2,
7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8,
2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11
};
void chaifen(char byte, int a[64], int q) {
int i;
for (i = 0; i < 8; i++) {
a[7 - i + q] = byte & 1;
byte >>= 1;
//把byte右移一位的值赋值给byte
}
}
void DES::set_key(unsigned char const* yonghu_key/*用户输入的64位密钥首地址*/) {
//密钥扩展算法
int arr[64];
int ary[56];
int i, curry = 0;
for (i = 0; i < 8; i++) {
chaifen(yonghu_key[i], arr, curry);
curry = curry + 8;
}
for (i = 0; i < 56; i++) {
ary[i] = arr[PC1_Table[i] - 1];
}
for (i = 0; i < 16; i++) {
if (i == 0 || i == 1 || i == 8 || i == 15) {
int j, temp0, temp1;
temp0 = ary[0]; temp1 = ary[28];
for (j = 0; j < 28; j++) {
ary[j] = ary[j + 1];
ary[j + 28] = ary[j + 29];
}
ary[27] = temp0; ary[55] = temp1;
}
else {
int j, temp0, temp1;
temp0 = ary[0]; temp1 = ary[28];
for (j = 0; j < 28; j++) {
ary[j] = ary[j + 1];
ary[j + 28] = ary[j + 29];
}
ary[27] = temp0; ary[55] = temp1;
temp0 = ary[0]; temp1 = ary[28];
for (j = 0; j < 28; j++) {
ary[j] = ary[j + 1];
ary[j + 28] = ary[j + 29];
}
ary[27] = temp0; ary[55] = temp1;
}
int j;
for (j = 0; j < 48; j++)
enckey[i][j] = (bool)ary[PC2_Table[i] - 1];
}
}
void DES::en_ctransform(const unsigned char* In /*待解密的64位数据首地址*/, unsigned char* Out) {
//加密变换算法
int arr[64];
int ary[64];
int i, j, curry = 0;
for (i = 0; i < 8; i++) {
chaifen(In[i], arr, curry);
curry = curry + 8;
}
for (i = 0; i < 64; i++) {
ary[i] = arr[IP_Table[i] - 1];
}
int larr[32];
int rarr[32];
for (i = 0; i < 32; i++) {
larr[i] = ary[i];
rarr[i] = ary[i + 32];
}
for (i = 0; i < 16; i++) {
int temp[32];
for (j = 0; j < 32; j++) {
temp[j] = larr[j];
larr[j] = rarr[j];
}
int i0, j0, q;
int e[48];
for (i0 = 0; i0 < 48; i0++)
e[i0] = rarr[E_Table[i0] - 1];
int w;
for (w = 0; w < 48; w++) {
e[w] = (e[w] + enckey[i][w]) % 2;
}
for (j0 = 0; j0 < 8; j0++) {
int hang = e[j0 * 6] * 2 + e[j0 * 6 + 5];
int lie = e[j0 * 6 + 1] * 8 + e[j0 * 6 + 2] * 4 + e[j0 * 6 + 3] * 2 + e[j0 * 6 + 4];
int num = S_Box[j0][hang][lie];
for (q = 0; q < 4; q++) {
rarr[j0 * 4 + 3 - q] = num & 1;
num >>= 1;
}
}
int temp0[32];
for (j = 0; j < 32; j++) {
temp0[j] = rarr[j];
}
for (j = 0; j < 32; j++) {
rarr[j] = temp0[P_Table[j] - 1];
}
for (j = 0; j < 32; j++) {
rarr[j] = ((rarr[j] + temp[j]) % 2);
}
}
int temp[32];
for (i = 0; i < 32; i++) {
temp[i] = larr[i];
larr[i] = rarr[i];
rarr[i] = temp[i];
}
for (i = 0; i < 32; i++) {
ary[i] = larr[i];
ary[i + 32] = rarr[i];
}
for (i = 0; i < 64; i++) {
arr[i] = ary[IPR_Table[i] - 1];
}
for (i = 0; i < 8; i++) {
Out[i] = arr[i * 8] * 128 + arr[i * 8 + 1] * 64 + arr[i * 8 + 2] * 32 + arr[i * 8 + 3] * 16 + arr[i * 8 + 4] * 8 + arr[i * 8 + 5] * 4 + arr[i * 8 + 6] * 2 + arr[i * 8 + 7];
}
}
void DES::de_ctransform(const unsigned char* In /*待加密的64位数据首地址*/, unsigned char* Out) {
//解密变换算法
int arr[64];
int ary[64];
int i, j, curry = 0;
for (i = 0; i < 8; i++) {
chaifen(In[i], arr, curry);
curry += 8;
}
for (i = 0; i < 64; i++) {
ary[i] = arr[IP_Table[i] - 1];
}
int larr[32];
int rarr[32];
for (i = 0; i < 32; i++) {
larr[i] = ary[i];
rarr[i] = ary[i + 32];
}
for (i = 0; i < 16; i++) {
int temp[32];
for (j = 0; j < 32; j++) {
temp[j] = larr[j];
larr[j] = rarr[j];
}
int i0, j0, q;
int e[48];
for (i0 = 0; i0 < 48; i0++)
e[i0] = rarr[E_Table[i0] - 1];
int w;
for (w = 0; w < 48; w++) {
e[w] = (e[w] + enckey[15 - i][w]) % 2;
}
for (j0 = 0; j0 < 8; j0++) {
int hang = e[j0 * 6] * 2 + e[j0 * 6 + 5];
int lie = e[j0 * 6 + 1] * 8 + e[j0 * 6 + 2] * 4 + e[j0 * 6 + 3] * 2 + e[j0 * 6 + 4];
int num = S_Box[j0][hang][lie];
for (q = 0; q < 4; q++) {
rarr[j0 * 4 + 3 - q] = num & 1;
num >>= 1;
}
}
int temp0[32];
for (j = 0; j < 32; j++) {
temp0[j] = rarr[j];
}
for (j = 0; j < 32; j++) {
rarr[j] = temp0[P_Table[j] - 1];
}
for (j = 0; j < 32; j++) {
rarr[j] = ((rarr[j] + temp[j]) % 2);
}
}
int temp[32];
for (i = 0; i < 32; i++) {
temp[i] = larr[i];
larr[i] = rarr[i];
rarr[i] = temp[i];
}
for (i = 0; i < 32; i++) {
ary[i] = larr[i];
ary[i + 32] = rarr[i];
}
for (i = 0; i < 64; i++) {
arr[i] = ary[IPR_Table[i] - 1];
}
for (i = 0; i < 8; i++) {
Out[i] = arr[i * 8] * 128 + arr[i * 8 + 1] * 64 + arr[i * 8 + 2] * 32 + arr[i * 8 + 3] * 16 + arr[i * 8 + 4] * 8 + arr[i * 8 + 5] * 4 + arr[i * 8 + 6] * 2 + arr[i * 8 + 7];
}
}
int main() {
unsigned int seq[8];
unsigned char key[9]; //密钥
unsigned char plain[9]; //明文
unsigned char cipher[9];//密文
char shuruzi[17]; //键盘输入的字符
char choice = ' ';
DES mydes; //类
int i, j;
int s;
while (true) {
cout << "You are welcome to use the DES machine in SDU\n" << endl;
do {
cout << "Please enter the corresponding operation number:\n1.Encrypt\t2.Decrypt\t3.Quit" << endl;
scanf("\n%c", &choice);
} while (choice != '1' && choice != '2' && choice != '3');
switch (choice) {
case '1':
printf("Please enter the secret key (length = 16):\n");
scanf("%s", shuruzi);
sscanf(shuruzi, "%2x%2x%2x%2x%2x%2x%2x%2x", &seq[0], &seq[1], &seq[2], &seq[3], &seq[4], &seq[5], &seq[6], &seq[7]);
for (i = 0; i < 8; i++)
key[i] = seq[i];
//将输入的字符依次存到密钥数组中
printf("\n");
printf("Please enter plaintext (length = 16):\n");
scanf("%s", shuruzi);
printf("\n");
sscanf(shuruzi, "%2x%2x%2x%2x%2x%2x%2x%2x", &seq[0], &seq[1], &seq[2], &seq[3], &seq[4], &seq[5], &seq[6], &seq[7]);
for (j = 0; j < 8; j++)
plain[j] = seq[j];
//将输入的字符依次存到明文数组中
mydes.set_key(key);
mydes.en_ctransform(plain, cipher);
//调用加密算法函数完成加密
for (s = 0; s < 8; s++)
seq[s] = cipher[s];
printf("ciphertext:\n%02x%02x%02x%02x%02x%02x%02x%02x\n", seq[0], seq[1], seq[2], seq[3], seq[4], seq[5], seq[6], seq[7]);
//将密文数组中的字符存入缓存数组并输出
printf("\n");
break;
case '2':
printf("Please enter the secret key (length = 16):\n");
scanf("%s", shuruzi);
sscanf(shuruzi, "%2x%2x%2x%2x%2x%2x%2x%2x", &seq[0], &seq[1], &seq[2], &seq[3], &seq[4], &seq[5], &seq[6], &seq[7]);
for (i = 0; i < 8; i++)
key[i] = seq[i];
//将输入的字符依次存到明文数组中
printf("\n");
printf("Please enter the ciphertext (length = 16):\n");
scanf("%s", shuruzi);
printf("\n");
sscanf(shuruzi, "%2x%2x%2x%2x%2x%2x%2x%2x", &seq[0], &seq[1], &seq[2], &seq[3], &seq[4], &seq[5], &seq[6], &seq[7]);
for (j = 0; j < 8; j++)
cipher[j] = seq[j];
//将输入的字符依次存到密文数组中
mydes.set_key(key);
mydes.de_ctransform(cipher, plain);
//调用解密算法函数完成解密
for (s = 0; s < 8; s++)
seq[s] = plain[s];
printf("plaintext:\n%02x%02x%02x%02x%02x%02x%02x%02x\n", seq[0], seq[1], seq[2], seq[3], seq[4], seq[5], seq[6], seq[7]);
printf("\n");
break;
case '3':
return 0;
break;
}
}
}Test sample：
此处假定测试密钥为1234567891234561，设置测试明文为7894561237894569，进行加密得到密文，再对密文进行解密，经验证可以得到明文，DES程序运行成功。
3. summary and harvest
在一开始编程时我不知道从何写起，在仔细看完信息安全的有关原理后，我逐渐有了思路，按照整个算法的细分流程编写代码。先初始置换IP，定义S盒等，再编写相同结构的16轮迭代，每轮中都有置换和代换运算，第16轮变换的输出分为左、右两半，并交换次序。最后逆初始置换IP-1（IP的逆）后，产生64bit的密文。
在定义S_Box的时候，起初我是分开定义每个盒的，将每个S盒定义为2维矩阵，但是这样定义不够简洁，在将48位数据按照每6位分为一组，一共分为8组，并分别输入S1， S2，S3，S4，S5，S6，S7，S8这8个盒子中，每个盒子产生4位的输出，将每个S 盒的输出拼接成32位的过程中，调用很容易出错。通过查阅资料，找到了完美解决这个问题的方法，将S盒定义为3维数组，并且可以直接将S盒中所有元素添加进去，由于C++特性，可以按数组特性自动归类，很大程度上方便了后续调用。
初学信息安全，可能存在错误之处，还请各位不吝赐教。
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
