DES算法 C语言实现
DES算法C语言实现
算法概述
DES算法是一种对称块加密方法，加密和解密都使用一个长度为64位的密钥。以64位为一个分组长度，对于每个分组，通过置换、Feistel轮函数、子密钥生成等一系列操作，输出一段64位的密文。在解密过程中，更换子密钥输入的顺序，即可解出原本的明文。
总体结构
- 对输入的64位密文进行一次IP置换，得到 L 0 R 0 L_0R_0 L0R0
- 对IP置换的结果进行16次迭代，迭代的规则为：
L i = R ( i − 1 ) , R i = L ( i − 1 ) ⨁ f ( R ( i − 1 ) , K i ) L_i = R_(i-1), R_i = L_(i-1) \bigoplus f(R_(i-1),K_i) Li=R(i−1),Ri=L(i−1)⨁f(R(i−1),Ki) - 子密钥的生成以输入的64密钥为基础，经过PC1置换、循环移位和PC2置换等过程生成16个48位的字密钥，依次输入到Feistel函数中。
- 16次迭代完成后，将前32位与后32位交换位置，进行一次IP逆置换，得到最终的密文。
代码实现
- tables.h：定义了DES算法过程用到的所有数组
- utility.h：所有模块函数的定义与实现
- main.cpp：处理输入输出。
#pragma once
#include #pragma once
#include "tables.h"
void charToBit(char * msg, int* msgBit) {
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
msgBit[(i + 1) * 8 - j - 1] = (msg[i] >> j) & 1;
}
}
}
void BitToChar(int* msgBit, char* msg) {
int sum = 0;
int count = 0;
for (int i = 0; i < 64; i++) {
sum = sum * 2 + msgBit[i];
if (i % 8 == 7) {
msg[count++] = sum;
sum = 0;
}
}
}
void IP_Permutation(int* input, int* output) {
for (int i = 0; i < 64; i++) {
output[i] = input[IP_Table[i] - 1];
}
}
void IP_Reverse_Permutation(int* input, int* output) {
for (int i = 0; i < 64; i++) {
output[i] = input[IP_Reverse_Table[i] - 1];
}
}
void devision(int* input, int *L, int* R) {
for (int i = 0; i < 32; i++) {
L[i] = input[i];
R[i] = input[i + 32];
}
}
void Extension(int* R, int* extendedR) {
for (int i = 0; i < 48; i++) {
extendedR[i] = R[Extension_Table[i] - 1];
}
}
void Xor48(int* R, int* subkey) {
for (int i = 0; i < 48; i++) {
if (R[i] != subkey[i]) {
R[i] = 1;
}
else {
R[i] = 0;
}
}
}
void Xor32(int* R, int* subkey) {
for (int i = 0; i < 32; i++) {
if (R[i] != subkey[i]) {
R[i] = 1;
}
else {
R[i] = 0;
}
}
}
void SBox(int* input, int start, int* output, int* SBox) {
int row = input[start] * 2 + input[start + 5];
int col = 0;
for (int i = 1; i <= 4; i++) {
col = col * 2 + input[start + i];
}
int result = SBox[row * 16 + col];
for (int i = 0; i < 4; i++) {
output[3 - i] = (result >> i) & 1;
}
}
void P_Permutation(int* input, int* output) {
for (int i = 0; i < 32; i++) {
output[i] = input[P_Table[i] - 1];
}
}
void Feistel(int* R, int* subkey, int* output) {
int extendedR[48] = { 0 };
Extension(R, extendedR);
Xor48(extendedR, subkey);
int SBoxResult[8][4] = { 0 };
for (int i = 0; i < 8; i++) {
SBox(extendedR, i * 6, SBoxResult[i], S_Box[i]);
}
//将SBox结果连接起来
int totalSBox[32] = { 0 };
for (int i = 0; i < 32; i++) {
totalSBox[i] = SBoxResult[i / 4][i % 4];
}
P_Permutation(totalSBox, output);
}
void leftShift(int* input) {
int first = input[0];
for (int i = 0; i < 27; i++) {
input[i] = input[i + 1];
}
input[27] = first;
}
void PC1(int* input, int* key) {
for (int i = 0; i < 56; i++) {
input[i] = key[PC1_Table[i] - 1];
}
}
void PC2(int* input, int* subkey) {
for (int i = 0; i < 48; i++) {
subkey[i] = input[PC2_Table[i] - 1];
}
}
void generateSubkeys(int key[64], int subkeys[16][48]) {
int pc1[56] = { 0 };
int pc2[56] = { 0 };
int C[28] = { 0 };
int D[28] = { 0 };
PC1(pc1, key);
for (int i = 0; i < 28; i++) {
C[i] = pc1[i];
D[i] = pc1[i + 28];
}
for (int i = 1; i < 17; i++) {
if (i == 1 || i == 2 || i == 9 || i == 16) {
leftShift(C);
leftShift(D);
}
else {
leftShift(C);
leftShift(C);
leftShift(D);
leftShift(D);
}
for (int i = 0; i < 28; i++) {
pc2[i] = C[i];
pc2[i + 28] = D[i];
}
PC2(pc2, subkeys[i - 1]);
}
}
void Swap(int* L, int * R) {
int* temp = L;
L = R;
R = temp;
}
void DES(int* msgBit, char* key) {
int keyBit[64] = { 0 };
int permutationBit[64] = { 0 }; //IP置换后的矩阵
int L[32] = { 0 }; //前32位
int R[32] = { 0 }; //后32位
int subkeys[16][48] = { 0 };
int iterationL[32] = { 0 }; //迭代后的L和R
int iterationR[32] = { 0 };
int cryptedMsg[64] = { 0 };
charToBit(key, keyBit);
IP_Permutation(msgBit, permutationBit);
devision(permutationBit, L, R);
generateSubkeys(keyBit, subkeys);
//迭代T
int FeistelResult[32] = { 0 };
for (int i = 0; i < 16; i++) {
for (int j = 0; j < 32; j++) {
iterationL[j] = R[j];
iterationR[j] = L[j];
}
Feistel(R, subkeys[i], FeistelResult);
Xor32(iterationR, FeistelResult);
for (int j = 0; j < 32; j++) {
L[j] = iterationL[j];
R[j] = iterationR[j];
}
}
//交换L和R的顺序并合并
int iterationTotal[64] = { 0 }; //迭代后的二进制
for (int i = 0; i < 32; i++) {
iterationTotal[i] = iterationR[i];
iterationTotal[i + 32] = iterationL[i];
}
IP_Reverse_Permutation(iterationTotal, cryptedMsg);
printf("\nThe crypeted message is :\n");
for (int i = 0; i < 64; i++) {
printf("%d", cryptedMsg[i]);
}
}
void Decrypt(int* msgBit, char* key) {
int keyBit[64] = { 0 };
int permutationBit[64] = { 0 }; //IP置换后的矩阵
int L[32] = { 0 }; //前32位
int R[32] = { 0 }; //后32位
int subkeys[16][48] = { 0 };
int iterationL[32] = { 0 }; //迭代后的L和R
int iterationR[32] = { 0 };
int decryptedBit[64] = { 0 };
charToBit(key, keyBit);
IP_Permutation(msgBit, permutationBit);
devision(permutationBit, L, R);
generateSubkeys(keyBit, subkeys);
//迭代T
int FeistelResult[32] = { 0 };
for (int i = 0; i < 16; i++) {
for (int j = 0; j < 32; j++) {
iterationL[j] = R[j];
iterationR[j] = L[j];
}
Feistel(R, subkeys[15 - i], FeistelResult);
Xor32(iterationR, FeistelResult);
for (int j = 0; j < 32; j++) {
L[j] = iterationL[j];
R[j] = iterationR[j];
}
}
//交换L和R的顺序并合并。
int iterationTotal[64] = { 0 };
for (int i = 0; i < 32; i++) {
iterationTotal[i] = iterationR[i];
iterationTotal[i + 32] = iterationL[i];
}
IP_Reverse_Permutation(iterationTotal, decryptedBit);
char decryptedMsg[9] = { 0 };
BitToChar(decryptedBit, decryptedMsg);
printf("\nThe decrypeted message is :\n");
for (int i = 0; i < 8; i++) {
printf("%c", decryptedMsg[i]);
}
printf("\n");
}
#include