DES加密算法
DES加密算法
参考
- 《密码编码与信息安全——C++实践》
- 参考“DES加密算法｜密码学｜信息安全” https://www.bilibili.com/video/BV1KQ4y127AT?from=search&seid=1358372623996612630&spm_id_from=333.337.0.0
本文将从基本原理，加密过程，子密钥生成过程对DES进行讲解。源码可在github中找到，文末也会贴出源码。
https://github.com/yingmuzhi/cryptology/blob/main/DES.cpp
基本原理
- DES算法是属于对称密码算法中的分组加密算法。
分组加密属于块加密，对一个字节块进行加密。与分组加密对应的是流加密，流加密指一个字节一个字节加密。 - 密钥长64bit，56bit参与运算，其余8bit为校验位。分别取自{8, 16, 24, 32, 40, 48, 56, 64}位。
- 当n个64bit明文数据块都经过DES加密处理后，所得到的n个64bit密文数据块串在一起就是密文。
加密过程
以论运算为主，共进行16次轮加密。每一次轮加密左边与f运算的R异或后变右边，右边变左边。
-
IP置换（Initial Permutations）
将原来的64bit二进制位重新排序 -
轮函数——E扩展置换
将32bit输入扩展为48bit输出
-
48bit明文和48bit密钥异或后，再使用8个S盒压缩处理得到32bit数据，这是一个非线性运算
-
P盒置换，32bit->32bit。再和L0异或
-
IPI置换
密钥生成
64bit密钥生成16个48bit的轮密钥
- 使用PC1置换算法，64bit->56bit
- 分组循环左移（若求解密密钥则是分组循环右移）
- 合并后使用PC2置换算法，56bit->48bit
源码：
/*
* @Descripttion: refer to "密码编码与信息安全:C++实践"
* @version:
* @Author: MuzhiYing
* @Date: 2022-03-23 14:36:55
* @LastEditors: MuzhiYing
* @LastEditTime: 2022-03-23 16:40:16
*/
#include
R = k&0x0000000FFFFFFF;
if(n == 1){
L = ((L&0x7FFFFFF)<<1) | ((L>>27)&1);
R = ((R&0x7FFFFFF)<<1) | ((R>>27)&1);
tempKey = (L<<28) | R;
}else if(n==2){
L = ((L&0x3FFFFFF)<<2) | ((L>>26)&3);
R = ((R&0x7FFFFFF)<<2) | ((R>>26)&3);
tempKey = (L<<28) | R;
}
return tempKey;
}
/// 根据数组要求，实现置换
unsigned long long DES::permutations(unsigned long long num, const int p[], int pmax, int n){
unsigned long long temp = 0;
int i;
for(i=0;i<n;i++){
temp <<= 1;
temp |= (num >> (pmax - p[i])) & 1;
}
return temp;
}
/// S盒运算
unsigned long long DES::SBoxes(unsigned long long num){
int i;
unsigned long long temp;
unsigned long long result = 0;
for (i=0; i<8; ++i){
temp = (num >> ((7-i) * 6)) & 0x3F;
int x = ((temp>>4) & 0x2) | (temp & 0x1) + i*4;
int y = (temp>>1) & 0xF;
temp = SBox[x][y];
temp = temp << ((7-i)*4);
result |= temp;
}
return result;
}
/// 加密总过程
void DES::encryption(){
unsigned long long temp = permutations(plainText, IP, 64, 64);
int i;
unsigned long long L, R, tempR;
L = (temp & 0xFFFFFFFF00000000LL) >> 32;
R = (temp & 0x00000000FFFFFFFFLL);
tempR = R;
for(i = 0; i<16; i++){
tempR = permutations(R, EP, 32, 48);
tempR = tempR ^ encKey[i];
tempR = SBoxes(tempR);
tempR = permutations(tempR, P, 32, 32);
tempR ^= L;
L = R;
R = tempR;
cout<<"L["<<i+1<<"]:"<<L<<";R["<<i+1<<"]:"<<R<<endl;
}
temp = (R<<32) | L;
temp = permutations(temp, IPI, 64, 64);
cipherText = temp;
}
/// 解密总过程
void DES::decryption(){
unsigned long long temp = permutations(cipherText, IP, 64, 64);
int i;
unsigned long long L, R, tempR;
L = (temp & 0xFFFFFFFF00000000LL) >> 32;
R = (temp & 0x00000000FFFFFFFFLL);
tempR = R;
for(i = 0; i<16; i++){
tempR = permutations(R, EP, 32, 48);
tempR = tempR ^ encKey[15-i]; // 密钥生成方顺序不同
tempR = SBoxes(tempR);
tempR = permutations(tempR, P, 32, 32);
tempR ^= L;
L = R;
R = tempR;
}
temp = (R<<32) | L;
temp = permutations(temp, IPI, 64, 64);
decipherText = temp;
}
/// 二进制结果展示
void DES::showBinary(unsigned long long num){
std::vector<int> v;
do{
v.push_back(num % 2);
num = (num - num%2) / 2;
}while(num != 0);
for(int i=(v.size()-1); i>=0; i--){
cout<<v[i];
}
cout<<endl;
}
/// 展示结果
void DES::showResult(){
int i;
cout << "key = ";
for(i = 0; i< 8; i++){
cout << (char) ((key>>(7-i) * 8)&0xFF);
}
cout << endl;
cout << "plainText = ";
for (i = 0; i< 8; i++){
cout << (char) ((plainText >> (7-i) * 8)& 0xFF);
}
cout << endl;
cout << "cipherText = ";
for (i = 0; i< 8; i++){
cout << (char) ((cipherText>>(7-i) *8)&0xFF);
}
cout << endl;
cout << "decipherText = ";
for (i = 0; i< 8; i++){
cout << (char)((decipherText>>(7-i)*8)&0xFF);
}
cout << endl;
}
/// main
int main(int argc, char const *argv[])
{
DES des;
des.setKey("01234567");
des.setPlainText("76543210");
des.genEncKey();
des.encryption();
des.decryption();
des.showResult();
return 0;
}