DES的原理
DES算法是一种对称加密算法，算法把64位明文输入块通过64位密钥变为64位密文输出块。
算法主要包括两个部分的内容：轮密钥生成；加解密。
整个算法的流程图如下图所示：
轮密钥生成过程
1： 对于输入的初始密钥（64位），首先经过一个 PC-1 置换，此时得到的密钥中间值为56比特。
2： 将56位比特数据分为 C 和 D 两个部分，分别为28比特。
3：对 C 和 D 进行循环左移，每一轮循环左移的位置是固定的。
4：经过循环左移之后得到新的 C 和 D ，将 C 和 D 合并，进行一个 PC-2 置换，即可得到第一轮子密钥。
5：循环步骤 2、3、4 得到所有的16轮子密钥。
6：密钥生成算法的流程图如下图所示：
加解密过程
以加密为例（解密的过程与加密的过程相似，只是轮密钥的使用顺序相反）
1：首先输入的64位明文进行一个初始IP置换，得到新的排列的64位明文中间值。
2：将这64位数值数据值分为 L 和 R 两部分，R 就是下一轮中要使用的 L
3：R 和轮密钥 K 进行 F 函数运算，结果和 L 进行异或，异或得到的结果就是下一轮中 R 的值。
4：经过16轮迭代之后对最后的 L 和 R 值合并并进行一个逆置换， 得到最终的64位密文。
5：加密过程的整体流程图如下图所示：
加解密过程中最终的一个步骤就是 F 函数
1：R 中的32位数据通过扩展置换 E 得到48位比特数据
2：这48位比特数据和轮密钥 Key 进行异或得到新的48位数据值
3：48位数据值经过 S 盒变换成为32比特数据值，最终通过一个 P 置换，得到整个最后的 F 函数的32位输出值。
4：F 函数的流程图如下图所示：
F 函数中最重要的一个就是 S 盒的变换
1：S 盒是指一个 4 X 16 的数组。
2：当一个6位的二进制数输入时，最高位和最低位组成一个二进制数，得到数组的行；剩余位同理得到列。
3：查找数组对应行列中的值，将其转换为一个4比特的二进制数，就是 S 盒的最终输出。
DES的C++实现
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
using namespace std;
string roundKey[16];
int PC1[] = { 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 };
string PC1Exchange(string key) {
string result = "";
for (int i = 0; i < 56; ++i) {
result += key[PC1[i]-1];
}
return result;
}
int LS[] = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };
string LeftShift(string key, int ShiftNumber) {
return key.substr(ShiftNumber) + key.substr(0, ShiftNumber);
}
int PC2[] = { 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 };
string PC2Exchange(string key) {
string result = "";
for (int i = 0; i < 48; ++i) {
result += key[PC2[i] - 1];
}
return result;
}
void KeyGenerate(string initKey) {
string leftKey;
string rightKey;
string tempKey = PC1Exchange(initKey);
for (int i = 0; i < 16; ++i) {
leftKey = tempKey.substr(0, 28);
rightKey = tempKey.substr(28);
leftKey = LeftShift(leftKey, LS[i]);
rightKey = LeftShift(rightKey, LS[i]);
tempKey = leftKey + rightKey;
roundKey[i] = PC2Exchange(tempKey);
}
}
int 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 };
string IPExchange(string init) {
string result = "";
for (int i = 0; i < 64; ++i) {
result += init[IP[i] - 1];
}
return result;
}
int E[] = { 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 };
string EExchange(string right) {
string result = "";
for (int i = 0; i < 48; ++i) {
result += right[E[i] - 1];
}
return result;
}
int SBOX[8][4][16] = {
{{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}},
{{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}},
{{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}},
{{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}},
{{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}},
{{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}},
{{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}},
{{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}}
};
string DecToBin(int str) {
string bin = "";
while (str >= 1) {
bin = to_string(str % 2) + bin;
str = str / 2;
}
while (bin.size() != 4) {
bin = '0' + bin;
}
return bin;
}
int BinToDec(char str) {
return str - '0';
}
string SExchange(string right) {
string result = "";
for (int i = 0; i < 48; i = i + 6) {
int row = BinToDec(right[i]) * 2 + BinToDec(right[i + 5]);
int col = BinToDec(right[i + 1]) * 8 + BinToDec(right[i + 2]) * 4 + BinToDec(right[i + 3]) * 2 + BinToDec(right[i + 4]);
result += DecToBin(SBOX[i / 6][row][col]);
}
return result;
}
int P[] = { 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 };
string PExchange(string right) {
string result = "";
for (int i = 0; i < 32; ++i) {
result += right[P[i] - 1];
}
return result;
}
string XOR(string str1, string str2) {
string res = "";
for (int i = 0; i < str1.size(); i++) {
if (str1[i] == str2[i]) {
res += "0";
}
else {
res += "1";
}
}
return res;
}
string F(string right, string key) {
string temp = EExchange(right);
temp = XOR(temp, key);
string result = SExchange(temp);
result = PExchange(result);
return result;
}
int IPR[] = { 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 };
string IPRExchange(string end) {
string result = "";
for (int i = 0; i < 64; ++i) {
result += end[IPR[i] - 1];
}
return result;
}
string encrypt(string plain, string key) {
string cipher = "";
string temp = IPExchange(plain);
string left = temp.substr(0, 32);
string right = temp.substr(32);
for (int i = 0; i < 16; i++) {
string middle = right;
right = XOR(left, F(right, roundKey[i]));
left = middle;
}
cipher = right + left;
cipher = IPRExchange(cipher);
return cipher;
}
string decrypt(string cipher, string key) {
string plain = "";
string temp = IPExchange(cipher);
string left = temp.substr(0, 32);
string right = temp.substr(32);
for (int i = 0; i < 16; ++i) {
string middle = right;
right = XOR(left, F(right, roundKey[15-i]));
left = middle;
}
plain = right + left;
plain = IPRExchange(plain);
return plain;
}
int HexToDec(char str) {
int dec = 0;
if (str >= 'A' && str <= 'F') {
dec += (str - 'A' + 10);
}
else {
dec += (str - '0');
}
return dec;
}
string HexToBin(string str) {
string bin = "";
string table[16] = { "0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111" };
for (int i = 0; i < str.size(); i++) {
if (str[i] >= 'A'&&str[i] <= 'F') {
bin += table[str[i] - 'A' + 10];
}
else {
bin += table[str[i] - '0'];
}
}
return bin;
}
string BinToHex(string str) {
string hex = "";
int temp = 0;
while (str.size() % 4 != 0) {
str = "0" + str;
}
for (int i = 0; i < str.size(); i += 4) {
temp = (str[i] - '0') * 8 + (str[i + 1] - '0') * 4 + (str[i + 2] - '0') * 2 + (str[i + 3] - '0') * 1;
if (temp < 10) {
hex += to_string(temp);
}
else {
hex += 'A' + (temp - 10);
}
}
return hex;
}
int main() {
string input = "0123456789ABCDEF";
string initKey = "133457799BBCDFF1";
string plain = HexToBin(input);
string key = HexToBin(initKey);
KeyGenerate(key);
string cipher = encrypt(plain, key);
cout << "明文： " << input << endl;
cout << "密钥： " << initKey << endl;
cout << "密文： " << cipher << endl;
string output = decrypt(cipher, key);
cout << "密文： " << cipher << endl;
cout << "密钥： " << initKey << endl;
cout << "明文： " << input << endl;
}
DES的C++实现结果
例：
明文： 0123456789ABCDEF
密钥： 133457799BBCDFF1
密文： 85E813540F0AB405
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