DES是一個16輪的Feistel型結構密碼，它的分組長度為64比特，用一個56比特的密鑰來加密一個64比特的明文串，輸出一個64比特的密文串。其中，使用密鑰為64比特，實用56比特，另8位用作奇偶校驗。加密的過程是先對64位明文分組進行初始置換，然后分左、右兩部分分別經過16輪迭代，然后再進行循環移位與變換，最后進行逆變換得出密文。加密與解密使用相同的密鑰，因而它屬于對稱密碼體制。假設輸入的明文數據是64比特。首先經過初始置換IP后把其左半部分32比特記為L0，右半部分32比特記為R0，即成了置換后的輸入；然后把R0與密鑰產生器產生的子密鑰k1進行運算，其結果計為f?(R0,k1);再與L0進行摸2加得到L0+f (R0 , k1), 把R0記為L1放在左邊，而把L0+f?(R0?, k1)記為R1放在右邊，從而完成了第一輪迭代運算。在此基礎上，重復上述的迭代過程，一直迭代至第16輪。所得的第16輪迭代結果左右不交換，即L15+f?(R15 , k16)記為R16,放在左邊，而R15記為L16放在右邊，成為預輸出，最后經過初始置換的逆置換IP-1運算后得到密文。詳細的算法解析在網上有很多，筆者在這里就不一一介紹，核心處理在于f函數，編程過程中謹慎一點兒別抄錯數字之類的，一般都沒問題。解密過程是加密的逆向，只需要在加密過程中把十六輪子秘鑰全部記錄下來，在解密時反過來使用一輪，其他的處理算法如出一轍，就能正確得出結果。直接在下面貼出代碼（代碼有局限，只能接受十六位十六進制數作為明文，十六位十六進制數作為初始秘鑰，對于中文的加密以及任意長度的字符串的加密，有需要的朋友可以自行修改代碼實現）。初始秘鑰和明文從文件中讀取，會在后面附上截圖。

// DES.cpp : 此文件包含 "main" 函數。程序執行將在此處開始并結束。 //#include "pch.h" #include <iostream> #include <fstream> #include <string> using namespace std;//記錄所有的子秘鑰 int eachKey[16][48];int boxS[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}} };//記錄左移次數 int leftMove[16] = { 1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1 };int C[28] = { 0 }, D[28] = { 0 }; int L[32] = { 1 }, R[32] = { 1 };//p置換 int P[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};//E擴展 int biteChoiceLabel[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};//秘鑰置換 int keySwap[8][6] = { {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} };//密文初始置換 int IP[8][8] = { {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 }};//密文逆置換 int IP_1[8][8] = { {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} };//64->56選擇 int PC_1[8][7] = { {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} };//初始置換IP void InitIP(int **input) {int s[64];int c = 0;for(int i = 0;i<8;i++)for (int j = 0; j < 8; j++) {s[c++] = input[i][j];}int **newIP = new int *[8];for (int i = 0; i < 8; i++)newIP[i] = new int[8];for (int i = 0; i < 8; i++) {for (int j = 0; j < 8; j++) {int loc = IP[i][j] - 1; //因為從1開始，這里下標減一newIP[i][j] = s[loc];}}int l = 0, m = 0;for(int i = 0;i < 8;i++)for (int j = 0; j < 8; j++) {if (i * 8 + j < 32)L[l++] = newIP[i][j];elseR[m++] = newIP[i][j];} }//逆初始置換 void reverse() {int temp[64];int a[64];for (int i = 0; i < 32; i++) {temp[i] = L[i];temp[i + 32] = R[i];}int l = 0, m = 0;for (int i = 0; i < 8; i++) {for (int j = 0; j < 8; j++) {a[l++] = temp[IP_1[i][j] - 1];}}l = 0;for (int i = 0; i < 64; i++)if (i < 32)L[l++] = a[i];elseR[m++] = a[i]; }//操作函數f int *f(int n, int flag) {int *result = new int[32];int a[48];int temp[56];int newKey[48];for (int i = 0; i < 28; i++) {temp[i] = C[i];temp[i + 28] = D[i];}int l = 0;if (flag == 0) {for (int i = 0; i < 8; i++) {for (int j = 0; j < 6; j++) {int loc = keySwap[i][j];newKey[l++] = temp[loc - 1];eachKey[15-n][l - 1] = newKey[l - 1]; //記錄加密時的全部子秘鑰}}}else {for (int i = 0; i < 48; i++)newKey[i] = eachKey[n][i];}int newR[48];for (int i = 0; i < 48; i++)newR[i] = R[biteChoiceLabel[i]-1];for (int i = 0; i < 48; i++)a[i] = (newKey[i]+newR[i])%2;int b[8][6];int r[8];l = 0;int m = 0;int k = 0;for (int i = 0; i < 48; i++) {b[l][m] = a[i];if ((i + 1) % 6 == 0) {int first = b[l][0] * 2 + b[l][5];int second = b[l][1] * 8 + b[l][2] * 4 + b[l][3] * 2 + b[l][4];r[l] = boxS[l][first][second];l++;m = 0;}elsem++;}int c[8][4];l = 0;for (int i = 0; i < 8; i++) {int ti = 0;int aa = r[i] / 8;int bb = (r[i] - aa * 8) / 4;int cc = (r[i] - aa * 8 - bb * 4) / 2;int dd = r[i] - aa * 8 - bb * 4 - cc * 2;c[i][0] = aa;c[i][1] = bb;c[i][2] = cc;c[i][3] = dd;}int tempP[32];for (int i = 0; i < 8; i++)for (int j = 0; j < 4; j++) {tempP[l++] = c[i][j];}for (int i = 0; i < 32; i++)result[i] = tempP[P[i] - 1];return result; }//交換處理 void swap(int n, int flag) {int tempL[32], tempR[32];int *Result = new int[32];//數據備份for (int i = 0; i < 32; i++) {tempR[i] = R[i];tempL[i] = L[i];}Result = f(n, flag);//數據更新計for (int i = 0; i < 32; i++) {L[i] = tempR[i];R[i] = (tempL[i] + Result[i]) % 2;}if (n == 15) {for (int i = 0; i < 32; i++) {int temp = L[i];L[i] = R[i];R[i] = temp;}} }//產生第一輪秘鑰（64位->56位) int **firstKey(int **key) {int **fk = new int *[8];for (int i = 0; i < 8; i++)fk[i] = new int[7];int nk[64];int s = 0;int l = 0, m = 0;for (int i = 0; i < 8; i++)for (int j = 0; j < 8; j++)nk[s++] = key[i][j];for (int i = 0; i < 8; i++) {for (int j = 0; j < 7; j++) {int loc = PC_1[i][j] - 1;fk[i][j] = nk[loc];if (l < 28)C[l++] = nk[loc];elseD[m++] = nk[loc];}}return fk; }//循環產生子秘鑰 void nextKeyLeft(int n) {int times = leftMove[n];for (int i = 0; i < times; i++) {int C0 = C[0];int D0 = D[0];for (int j = 1; j < 28; j++) {C[j - 1] = C[j];D[j - 1] = D[j];}C[27] = C0;D[27] = D0;} }//十六進制輸入轉二進制 int **hxTobin(string input) {int a[64];int x[16];int **init_letters = new int *[8];for (int i = 0; i < 8; i++)init_letters[i] = new int[8];int j = 0;for (int i = 0; i < 16; i++) {if (input[i] >= '0' && input[i] <= '9')x[i] = input[i] - 48;else if (input[i] >= 'A' && input[i] <= 'Z')x[i] = input[i] - 55;elsex[i] = input[i] - 87;}for (int i = 0; i < 16; i++) {int aa = x[i] / 8;int bb = (x[i] - aa * 8) / 4;int cc = (x[i] - aa * 8 - bb * 4) / 2;int dd = x[i] - aa * 8 - bb * 4 - cc * 2;a[j] = aa;a[j + 1] = bb;a[j + 2] = cc;a[j + 3] = dd;j = j + 4;}int l = 0;for (int i = 0; i < 8; i++) {for (j = 0; j < 8; j++) {init_letters[i][j] = a[l++];}}return init_letters; }//二進制密文轉十六進制密文 string binTohx(int a[]) {string res;res.resize(16);int j = 0;for (int i = 0; i < 64; i+=4) {int b = a[i] * 8 + a[i + 1] * 4 + a[i + 2] * 2 + a[i + 3];if (b < 10)res[j] = b+'0';else{switch (b) {case 10:res[j] = 'a';break;case 11:res[j] = 'b';break;case 12:res[j] = 'c';break;case 13:res[j] = 'd';break;case 14:res[j] = 'e';break;case 15:res[j] = 'f';break;}}j++;}return res; }//解密過程 void decode(string res) {int **re = new int *[8];for (int i = 0; i < 8; i++)re[i] = new int[8];re = hxTobin(res);InitIP(re);for (int i = 0; i < 16; i++) {swap(i, 1);}reverse();int a[64];for (int i = 0; i < 32; i++) {a[i] = L[i];a[i + 32] = R[i];}string input;input = binTohx(a);std::cout << input << endl << endl;; }int main() {string letters;string keys;string words;char flag='n';int miwen[64];ifstream file;file.open("test.txt");int **fir = new int *[8];for (int i = 0; i < 8; i++)fir[i] = new int[8];cout << "--------- Begin(y/n)? ----------" << endl;cin >> flag;while (flag == 'y' &&!file.eof()) {std::cout << "---------- 讀入密文: ----------" << endl;if (!file) {std::cout << "---------- 讀取失敗 ----------" << endl;exit(0);}getline(file, letters);std::cout << "明文: " << letters << endl << endl;std::cout << "---------- 讀入秘鑰: ----------" << endl;getline(file, keys);std::cout << "秘鑰: " << keys << endl << endl;fir = hxTobin(keys);int **getLetters = new int *[8];for (int i = 0; i < 8; i++)getLetters[i] = new int[8];getLetters = hxTobin(letters);InitIP(getLetters);int **fk = new int *[8];for (int i = 0; i < 8; i++)fk[i] = new int[7];for (int i = 0; i <= 16; i++) {if (i == 0) {fk = firstKey(fir);}else {nextKeyLeft(i - 1);swap(i - 1, 0);}}reverse();int k = 0;for (int i = 0; i < 32; i++) {miwen[k++] = L[i];}for (int i = 0; i < 32; i++) {miwen[k++] = R[i];}words = binTohx(miwen);std::cout << "密文: " << words << endl;std::cout << "---------- 解密中 ----------" << endl;decode(words);std::cout << "----------- 繼續(y/n) ---------" << endl;std::cin >> flag;}std::cout << "---------- End! ----------" << endl;return 0; }

測試數據如下圖：奇數行是明文，偶數行是對應的測試秘鑰

運行截圖：

尊重原作，轉載請注明，轉載自：https://blog.csdn.net/kr2563

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