一、实验目的
熟悉 DES 加密的基本思路和流程，完成 DES 加密算法。
二、实验任务
1．编程实现 IP 初始置换表和初始 IP 逆置换表置换过程；
2．编程实现生成子密钥组函数实现（包括循环左移、PC 置换等）；
3．编程实现f 函数（包括扩展置换、S 盒压缩置换等）；
4．整合加密部分，完成 DES 加密实现。
5．以加密部分位基础，完成解密部分（将加密时密钥的使用顺序反过来）。
三、实验内容
DES加密算法实现参考代码：
#include <iostream>
#include <string>
using namespace std;
// IP 初始置换表
const static int 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
};
// E 扩展表
const static int 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
};
// P 盒
const static int 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
};
// IP 逆置换表
const static int 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
};
// 密钥第一次置换表
const static int 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
};
// 密钥第二次置换表
const int 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
};
// S 盒
const static int S_BOX[8][4][16] = {
// s1
{
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
},
// s2
{
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
},
// s3
{
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
},
// s4
{
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
},
// s5
{
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
},
// s6
{
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
},
// s7
{
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
},
// s8
{
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
}
};
// 生成的 sub key，在第 1、2、9、16 轮循环左移 1 位，其他轮循环左移 2 位
// 这里为了使下标对应循环次数，在开头设置一位无用的0
const static int LEFT_SHIFT_TIMES[17] = {
0, 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1
};
/*
* 将 char 型转化为二进制形式
*/
void char_to_bits(const char input[8], int output[64]) {
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
output[7 * (i + 1) - j + i] = (input[i] >> j) & 1;
}
}
}
/*
* 将二进制形式转化为 char 型
*/
void bits_to_char(const int input[64], char output[8]) {
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
output[i] = (char) (output[i] * 2 + input[8 * i + j]);
}
}
}
/*
* 异或函数
* 将数组 arr_1 和 arr_2 进行异或操作，并且保存在 arr_1 中
* op_len 是进行异或的位数
*/
void arr_xor(int *arr_1, const int *arr_2, const int op_len) {
for (int i = 0; i < op_len; i++) {
arr_1[i] = arr_1[i] ^ arr_2[i];
}
}
/*
* IP 初始置换函数
* IP 根据 IP 初始置换表进行初始置换
*/
void pass_ip(const int input[64], int output[64]) {
for (int i = 0; i < 64; i++) {
output[i] = input[IP_TABLE[i] - 1];
}
}
/*
* E 扩展置换函数
* 根据 E 扩展表进行扩展
*/
void pass_ext(const int input[32], int output[48]) {
for (int i = 0; i < 48; i++) {
output[i] = input[E_TABLE[i] - 1];
}
}
/*
* P 置换函数
* 根据 P 盒进行置换
*/
void pass_p_box(const int input[32], int output[32]) {
for (int i = 0; i < 32; i++) {
output[i] = input[P_TABLE[i] - 1];
}
}
/*
* IP 逆置换函数
* IP 根据 IP 逆置换表进行置换
*/
void pass_ipr(const int input[64], int output[64]) {
for (int i = 0; i < 64; i++) {
output[i] = input[IPR_TABLE[i] - 1];
}
}
/*
* 密匙第一次置换函数
* 根据密匙第一次置换表进行置换
*/
void pass_pc_1(const int input[64], int output[56]) {
for (int i = 0; i < 56; i++) {
output[i] = input[PC1_TABLE[i] - 1];
}
}
/*
* 密匙第二次置换函数
* 根据密匙第二次置换表进行置换
*/
void pass_pc_2(const int input[56], int output[48]) {
for (int i = 0; i < 48; i++) {
output[i] = input[PC2_TABLE[i] - 1];
}
}
/*
* S 盒压缩函数
* 根据 8 个 S 盒进行压缩
*/
void pass_s_box(const int input[48], int output[32]) {
int INT[8];
for (int i = 0, j = 0; i < 48; i = i + 6, j++) {
int row = (input[i] << 1) + (input[i + 5]);
int column = (input[i + 1] << 3) + (input[i + 2] << 2) + (input[i + 3] << 1) + (input[i + 4]);
INT[j] = S_BOX[j][row][column];
}
for (int j = 0; j < 8; j++) {
for (int i = 0; i < 4; i++) {
output[3 * (j + 1) - i + j] = (INT[j] >> i) & 1;
}
}
}
/*
* 轮迭代函数
*/
void f_func(const int input[32], int output[32], int sub_key[48]) {
int after_ext[48] = {0};
int after_s_box[32] = {0};
pass_ext(input, after_ext);
arr_xor(after_ext, sub_key, 48);
pass_s_box(after_ext, after_s_box);
pass_p_box(after_s_box, output);
}
/*
* 密匙循环左移函数
* 密匙在不同轮数都要进行不同的左移操作
*/
void rotate_left_shift(const int input[28], int output[28], int leftCount) {
for (int i = 0; i < 28; i++) {
output[i] = input[(i + leftCount) % 28];
}
}
/*
* 子密匙生成函数
* 生成 subKey，在第 1、2、9、16 轮循环左移 1 位，其他轮循环左移 2 位
*/
void gen_sub_key(const int input[64], int sub_keys[16][48]) {
int c[28], d[28];
int pc_1[56] = {0};
int pc_2[16][56] = {0};
int rotate_l_c[16][28] = {0};
int rotate_l_d[16][28] = {0};
// 经过第一次 pc 置换
pass_pc_1(input, pc_1);
for (int i = 0; i < 28; i++) {
c[i] = pc_1[i];
d[i] = pc_1[i + 28];
}
// 循环左移
for (int i = 1; i < 17; i++) {
rotate_left_shift(c, rotate_l_c[i - 1], LEFT_SHIFT_TIMES[i]);
rotate_left_shift(d, rotate_l_d[i - 1], LEFT_SHIFT_TIMES[i]);
}
// 合并
for (int i = 0; i < 16; i++) {
for (int j = 0; j < 28; j++) {
pc_2[i][j] = rotate_l_c[i][j];
pc_2[i][j + 28] = rotate_l_d[i][j];
}
}
// 经过第二次 pc 置换
for (int i = 0; i < 16; i++) {
pass_pc_2(pc_2[i], sub_keys[i]);
}
}
/*
* DES 加密函数
* 传入明文 input 和密匙 inKey，获取 64 位二进制密文 output
*/
void encrypt(const char input[8], char key[8], int output[64]) {
int ip[64] = {0};
int output_1[64] = {0};
int sub_keys[16][48];
int char_to_bit[64] = {0};
int bin_key[64];
int l[17][32], r[17][32];
char_to_bits(input, char_to_bit);
pass_ip(char_to_bit, ip);
char_to_bits(key, bin_key);
gen_sub_key(bin_key, sub_keys);
for (int i = 0; i < 32; i++) {
l[0][i] = ip[i];
r[0][i] = ip[32 + i];
}
for (int j = 1; j < 17; j++) {
for (int k = 0; k < 32; k++) {
if (j == 16) { // 第 16 轮迭代特殊处理
r[j][k] = r[j - 1][k];
} else {
l[j][k] = r[j - 1][k];
}
}
if (j == 16) { // 第 16 轮迭代特殊处理
f_func(r[j - 1], l[j], sub_keys[j - 1]);
arr_xor(l[j], l[j - 1], 32);
} else {
f_func(r[j - 1], r[j], sub_keys[j - 1]);
arr_xor(r[j], l[j - 1], 32);
}
}
for (int t = 0; t < 32; t++) {
output_1[t] = l[16][t];
output_1[32 + t] = r[16][t];
}
pass_ipr(output_1, output);
}
/*
* DES 解密函数
* 传入 64 位二进制密文 input 和密匙 key 获取明文 output
*/
void decrypt(const int input[64], const char key[64], char output[64]) {
int after_ip[64] = {0};
int output_1[64] = {0};
int output_2[64] = {0};
int sub_keys[16][48];
int bin_key[64];
int l[17][32], r[17][32];
pass_ip(input, after_ip);
char_to_bits(key, bin_key);
gen_sub_key(bin_key, sub_keys);
for (int i = 0; i < 32; i++) {
l[0][i] = after_ip[i];
r[0][i] = after_ip[32 + i];
}
// 16次迭代处理
for (int j = 1; j < 17; j++) {
for (int k = 0; k < 32; k++) {
if (j == 16) { // 第 16 轮迭代特殊处理
r[j][k] = r[j - 1][k];
} else {
l[j][k] = r[j - 1][k];
}
}
if (j == 16) { // 第 16 轮迭代特殊处理
// 解密时，子密钥反过来用
f_func(r[j - 1], l[j], sub_keys[16 - j]);
arr_xor(l[j], l[j - 1], 32);
} else {
// 解密时，子密钥反过来用
f_func(r[j - 1], r[j], sub_keys[16 - j]);
arr_xor(r[j], l[j - 1], 32);
}
}
for (int t = 0; t < 32; t++) {
output_1[t] = l[16][t];
output_1[32 + t] = r[16][t];
}
pass_ipr(output_1, output_2);
bits_to_char(output_2, output);
}
int main() {
int encrypted[64] = {0};
// 字符数组最后要有一个'\0' 因此长一位
char origin[9] = {0};
char key[9] = {0};
cout << "请输入8位明文: " << endl;
cin >> origin;
cout << "请输入8位密钥: " << endl;
cin >> key;
encrypt(origin, key, encrypted);
cout << "加密后: " << endl;
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 16; j++) {
cout << encrypted[i * 4 + j];
}
cout << endl;
}
decrypt(encrypted, key, origin);
cout << "解密后: " << endl;
cout << origin;
return 0;
}
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