轉載請說明出處:http://www.iteye.com/topic/478024
DES(Data Encrypt Standard數據庫加密標準)是迄今爲止使用最廣泛的加密體制。
初學信息安全的新生,一般都會被老師要求實現DES算法,如果老師不要求,那麼有緣來我這裏共同學習的朋友,我建議你用C去實現一下,C語言在信息安全領域很重要,更何況隸屬於工科的信息安全,你只懂理論是遠遠不夠的。
想用其他語言實現的朋友,如果你用了彙編,那麼請您老人家走開不要來看小弟的笑話。如果你用C++或者JAVA,那麼我勸您用C吧,因爲2年前本人計算過速度,在我的機器上,同樣的代碼,用C++新建的工程要比用C新建的工程慢了2倍。至於JAVA,我估計要慢10倍。
廢話不多說,DES算法的理論我就不聒噪了,想要了解其實現的人,如果不懂其理論就來看這文章,即便是看懂了也會走火入魔,或者是某位學生心懷不軌。
一個加密算法的實現,最最重要的關鍵詞是—速度。
舉個例子來說明,速度對加密算法的重要:假設我們實現了兩個加密算法DES1.0和DES2.0,其中DES1.0的速度爲900KB/S,DES2.0的速度爲1000KB/S。假設一個文件有10G,我需要對其進行加密,那麼,用DES1.0所耗費的時間爲1111s,DES2.0的速度爲1000S。DES2.0比DES1.0快了111秒。現實生活裏我們要加密的數據還可能遠遠不止10G。
不要小看這111S,要知道,讓CPU儘可能的爲用戶服務,是我們每一個程序員的職責,不論你是用C,C++還是JAVA。
因此,爲了速度,我們必須捨棄一些東西。
有的同學喜歡用動態數組,因爲這也是個好東西,可以節約空間,於是有人認爲用了動態數組的程序比不用動態數組的程序要高了好幾級。
動態數組貌似高深,但如果你用在加密算法裏,我只能說這位同學啊你真是吃力不討好,在計算機世界裏,往往靜態的東西就是比動態的東西速度要快。
在此我首先聲明,如果你不是在練習結構體和malloc/calloc的使用,那麼請你果斷捨棄這些在加密算法裏華而不實的東西。
好了,說了這麼多,各位看官都等急了吧,下面我就結合DES算法原理來分步驟講解我的代碼。
一、準備
首先,頭文件與宏定義。
- #include "stdio.h"
- #include "memory.h"
- #include "time.h"
- #include "stdlib.h"
- #define PLAIN_FILE_OPEN_ERROR -1
- #define KEY_FILE_OPEN_ERROR -2
- #define CIPHER_FILE_OPEN_ERROR -3
- #define OK 1
其次,對基本數據類型進行typedef。
這句是不可以少的,請養成良好習慣,不然以後如果你要修改基本數據類型,累死你。
- typedef char ElemType;
而後,是初始置換表,逆初始置換表,S-Box等已知數據。
- //初始置換表IP
- int IP_Table[64] = { 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,
- 56,48,40,32,24,16,8,0,
- 58,50,42,34,26,18,10,2,
- 60,52,44,36,28,20,12,4,
- 62,54,46,38,30,22,14,6};
- //逆初始置換表IP^-1
- int IP_1_Table[64] = {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,
- 32,0,40,8,48,16,56,24};
- //擴充置換表E
- int E_Table[48] = {31, 0, 1, 2, 3, 4,
- 3, 4, 5, 6, 7, 8,
- 7, 8,9,10,11,12,
- 11,12,13,14,15,16,
- 15,16,17,18,19,20,
- 19,20,21,22,23,24,
- 23,24,25,26,27,28,
- 27,28,29,30,31, 0};
- //置換函數P
- int P_Table[32] = {15,6,19,20,28,11,27,16,
- 0,14,22,25,4,17,30,9,
- 1,7,23,13,31,26,2,8,
- 18,12,29,5,21,10,3,24};
- //S盒
- int S[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}}};
- //置換選擇1
- int PC_1[56] = {56,48,40,32,24,16,8,
- 0,57,49,41,33,25,17,
- 9,1,58,50,42,34,26,
- 18,10,2,59,51,43,35,
- 62,54,46,38,30,22,14,
- 6,61,53,45,37,29,21,
- 13,5,60,52,44,36,28,
- 20,12,4,27,19,11,3};
- //置換選擇2
- int PC_2[48] = {13,16,10,23,0,4,2,27,
- 14,5,20,9,22,18,11,3,
- 25,7,15,6,26,19,12,1,
- 40,51,30,36,46,54,29,39,
- 50,44,32,46,43,48,38,55,
- 33,52,45,41,49,35,28,31};
- //對左移次數的規定
- int MOVE_TIMES[16] = {1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};
二、模塊化。
對面向過程的程序,模塊化是否清晰是至關重要的。
下面是函數的聲明:
- int ByteToBit(ElemType ch,ElemType bit[8]);
- int BitToByte(ElemType bit[8],ElemType *ch);
- int Char8ToBit64(ElemType ch[8],ElemType bit[64]);
- int Bit64ToChar8(ElemType bit[64],ElemType ch[8]);
- int DES_MakeSubKeys(ElemType key[64],ElemType subKeys[16][48]);
- int DES_PC1_Transform(ElemType key[64], ElemType tempbts[56]);
- int DES_PC2_Transform(ElemType key[56], ElemType tempbts[48]);
- int DES_ROL(ElemType data[56], int time);
- int DES_IP_Transform(ElemType data[64]);
- int DES_IP_1_Transform(ElemType data[64]);
- int DES_E_Transform(ElemType data[48]);
- int DES_P_Transform(ElemType data[32]);
- int DES_SBOX(ElemType data[48]);
- int DES_XOR(ElemType R[48], ElemType L[48],int count);
- int DES_Swap(ElemType left[32],ElemType right[32]);
- int DES_EncryptBlock(ElemType plainBlock[8], ElemType subKeys[16][48], ElemType cipherBlock[8]);
- int DES_DecryptBlock(ElemType cipherBlock[8], ElemType subKeys[16][48], ElemType plainBlock[8]);
- int DES_Encrypt(char *plainFile, char *keyStr,char *cipherFile);
- int DES_Decrypt(char *cipherFile, char *keyStr,char *plainFile);
其實,模塊化與速度也是一對矛盾,因爲了解函數運行機制的人就知道,我們的計算機在運行某個函數時,是要用棧來保存入口狀態的,在運行結束後又要恢復現場,這些操作勢必會影像系統性能,但我們不能將所有代碼寫在Main函數裏,雖然那樣做我們的加密算法效率又會大增,但是那種代碼未免太過於醜陋不堪。因此,爲了帥,還是犧牲一下性能吧。
三、實現。
代碼裏能用移位操作都儘量用了移位操作,能用邏輯運算符的都用了邏輯運算符。
詳細的行注相信你可以看懂吧。有問題可以M我。
- //字節轉換成二進制
- int ByteToBit(ElemType ch, ElemType bit[8]){
- int cnt;
- for(cnt = 0;cnt < 8; cnt++){
- *(bit+cnt) = (ch>>cnt)&1;
- }
- return 0;
- }
- //二進制轉換成字節
- int BitToByte(ElemType bit[8],ElemType *ch){
- int cnt;
- for(cnt = 0;cnt < 8; cnt++){
- *ch |= *(bit + cnt)<<cnt;
- }
- return 0;
- }
- //將長度爲8的字符串轉爲二進制位串
- int Char8ToBit64(ElemType ch[8],ElemType bit[64]){
- int cnt;
- for(cnt = 0; cnt < 8; cnt++){
- ByteToBit(*(ch+cnt),bit+(cnt<<3));
- }
- return 0;
- }
- //將二進制位串轉爲長度爲8的字符串
- int Bit64ToChar8(ElemType bit[64],ElemType ch[8]){
- int cnt;
- memset(ch,0,8);
- for(cnt = 0; cnt < 8; cnt++){
- BitToByte(bit+(cnt<<3),ch+cnt);
- }
- return 0;
- }
- //生成子密鑰
- int DES_MakeSubKeys(ElemType key[64],ElemType subKeys[16][48]){
- ElemType temp[56];
- int cnt;
- DES_PC1_Transform(key,temp);//PC1置換
- for(cnt = 0; cnt < 16; cnt++){//16輪跌代,產生16個子密鑰
- DES_ROL(temp,MOVE_TIMES[cnt]);//循環左移
- DES_PC2_Transform(temp,subKeys[cnt]);//PC2置換,產生子密鑰
- }
- return 0;
- }
- //密鑰置換1
- int DES_PC1_Transform(ElemType key[64], ElemType tempbts[56]){
- int cnt;
- for(cnt = 0; cnt < 56; cnt++){
- tempbts[cnt] = key[PC_1[cnt]];
- }
- return 0;
- }
- //密鑰置換2
- int DES_PC2_Transform(ElemType key[56], ElemType tempbts[48]){
- int cnt;
- for(cnt = 0; cnt < 48; cnt++){
- tempbts[cnt] = key[PC_2[cnt]];
- }
- return 0;
- }
- //循環左移
- int DES_ROL(ElemType data[56], int time){
- ElemType temp[56];
- //保存將要循環移動到右邊的位
- memcpy(temp,data,time);
- memcpy(temp+time,data+28,time);
- //前28位移動
- memcpy(data,data+time,28-time);
- memcpy(data+28-time,temp,time);
- //後28位移動
- memcpy(data+28,data+28+time,28-time);
- memcpy(data+56-time,temp+time,time);
- return 0;
- }
- //IP置換
- int DES_IP_Transform(ElemType data[64]){
- int cnt;
- ElemType temp[64];
- for(cnt = 0; cnt < 64; cnt++){
- temp[cnt] = data[IP_Table[cnt]];
- }
- memcpy(data,temp,64);
- return 0;
- }
- //IP逆置換
- int DES_IP_1_Transform(ElemType data[64]){
- int cnt;
- ElemType temp[64];
- for(cnt = 0; cnt < 64; cnt++){
- temp[cnt] = data[IP_1_Table[cnt]];
- }
- memcpy(data,temp,64);
- return 0;
- }
- //擴展置換
- int DES_E_Transform(ElemType data[48]){
- int cnt;
- ElemType temp[48];
- for(cnt = 0; cnt < 48; cnt++){
- temp[cnt] = data[E_Table[cnt]];
- }
- memcpy(data,temp,48);
- return 0;
- }
- //P置換
- int DES_P_Transform(ElemType data[32]){
- int cnt;
- ElemType temp[32];
- for(cnt = 0; cnt < 32; cnt++){
- temp[cnt] = data[P_Table[cnt]];
- }
- memcpy(data,temp,32);
- return 0;
- }
- //異或
- int DES_XOR(ElemType R[48], ElemType L[48] ,int count){
- int cnt;
- for(cnt = 0; cnt < count; cnt++){
- R[cnt] ^= L[cnt];
- }
- return 0;
- }
- //S盒置換
- int DES_SBOX(ElemType data[48]){
- int cnt;
- int line,row,output;
- int cur1,cur2;
- for(cnt = 0; cnt < 8; cnt++){
- cur1 = cnt*6;
- cur2 = cnt<<2;
- //計算在S盒中的行與列
- line = (data[cur1]<<1) + data[cur1+5];
- row = (data[cur1+1]<<3) + (data[cur1+2]<<2)
- + (data[cur1+3]<<1) + data[cur1+4];
- output = S[cnt][line][row];
- //化爲2進制
- data[cur2] = (output&0X08)>>3;
- data[cur2+1] = (output&0X04)>>2;
- data[cur2+2] = (output&0X02)>>1;
- data[cur2+3] = output&0x01;
- }
- return 0;
- }
- //交換
- int DES_Swap(ElemType left[32], ElemType right[32]){
- ElemType temp[32];
- memcpy(temp,left,32);
- memcpy(left,right,32);
- memcpy(right,temp,32);
- return 0;
- }
- //加密單個分組
- int DES_EncryptBlock(ElemType plainBlock[8], ElemType subKeys[16][48], ElemType cipherBlock[8]){
- ElemType plainBits[64];
- ElemType copyRight[48];
- int cnt;
- Char8ToBit64(plainBlock,plainBits);
- //初始置換(IP置換)
- DES_IP_Transform(plainBits);
- //16輪迭代
- for(cnt = 0; cnt < 16; cnt++){
- memcpy(copyRight,plainBits+32,32);
- //將右半部分進行擴展置換,從32位擴展到48位
- DES_E_Transform(copyRight);
- //將右半部分與子密鑰進行異或操作
- DES_XOR(copyRight,subKeys[cnt],48);
- //異或結果進入S盒,輸出32位結果
- DES_SBOX(copyRight);
- //P置換
- DES_P_Transform(copyRight);
- //將明文左半部分與右半部分進行異或
- DES_XOR(plainBits,copyRight,32);
- if(cnt != 15){
- //最終完成左右部的交換
- DES_Swap(plainBits,plainBits+32);
- }
- }
- //逆初始置換(IP^1置換)
- DES_IP_1_Transform(plainBits);
- Bit64ToChar8(plainBits,cipherBlock);
- return 0;
- }
- //解密單個分組
- int DES_DecryptBlock(ElemType cipherBlock[8], ElemType subKeys[16][48],ElemType plainBlock[8]){
- ElemType cipherBits[64];
- ElemType copyRight[48];
- int cnt;
- Char8ToBit64(cipherBlock,cipherBits);
- //初始置換(IP置換)
- DES_IP_Transform(cipherBits);
- //16輪迭代
- for(cnt = 15; cnt >= 0; cnt--){
- memcpy(copyRight,cipherBits+32,32);
- //將右半部分進行擴展置換,從32位擴展到48位
- DES_E_Transform(copyRight);
- //將右半部分與子密鑰進行異或操作
- DES_XOR(copyRight,subKeys[cnt],48);
- //異或結果進入S盒,輸出32位結果
- DES_SBOX(copyRight);
- //P置換
- DES_P_Transform(copyRight);
- //將明文左半部分與右半部分進行異或
- DES_XOR(cipherBits,copyRight,32);
- if(cnt != 0){
- //最終完成左右部的交換
- DES_Swap(cipherBits,cipherBits+32);
- }
- }
- //逆初始置換(IP^1置換)
- DES_IP_1_Transform(cipherBits);
- Bit64ToChar8(cipherBits,plainBlock);
- return 0;
- }
- //加密文件
- int DES_Encrypt(char *plainFile, char *keyStr,char *cipherFile){
- FILE *plain,*cipher;
- int count;
- ElemType plainBlock[8],cipherBlock[8],keyBlock[8];
- ElemType bKey[64];
- ElemType subKeys[16][48];
- if((plain = fopen(plainFile,"rb")) == NULL){
- return PLAIN_FILE_OPEN_ERROR;
- }
- if((cipher = fopen(cipherFile,"wb")) == NULL){
- return CIPHER_FILE_OPEN_ERROR;
- }
- //設置密鑰
- memcpy(keyBlock,keyStr,8);
- //將密鑰轉換爲二進制流
- Char8ToBit64(keyBlock,bKey);
- //生成子密鑰
- DES_MakeSubKeys(bKey,subKeys);
- while(!feof(plain)){
- //每次讀8個字節,並返回成功讀取的字節數
- if((count = fread(plainBlock,sizeof(char),8,plain)) == 8){
- DES_EncryptBlock(plainBlock,subKeys,cipherBlock);
- fwrite(cipherBlock,sizeof(char),8,cipher);
- }
- }
- if(count){
- //填充
- memset(plainBlock + count,'\0',7 - count);
- //最後一個字符保存包括最後一個字符在內的所填充的字符數量
- plainBlock[7] = 8 - count;
- DES_EncryptBlock(plainBlock,subKeys,cipherBlock);
- fwrite(cipherBlock,sizeof(char),8,cipher);
- }
- fclose(plain);
- fclose(cipher);
- return OK;
- }
- //解密文件
- int DES_Decrypt(char *cipherFile, char *keyStr,char *plainFile){
- FILE *plain, *cipher;
- int count,times = 0;
- long fileLen;
- ElemType plainBlock[8],cipherBlock[8],keyBlock[8];
- ElemType bKey[64];
- ElemType subKeys[16][48];
- if((cipher = fopen(cipherFile,"rb")) == NULL){
- return CIPHER_FILE_OPEN_ERROR;
- }
- if((plain = fopen(plainFile,"wb")) == NULL){
- return PLAIN_FILE_OPEN_ERROR;
- }
- //設置密鑰
- memcpy(keyBlock,keyStr,8);
- //將密鑰轉換爲二進制流
- Char8ToBit64(keyBlock,bKey);
- //生成子密鑰
- DES_MakeSubKeys(bKey,subKeys);
- //取文件長度
- fseek(cipher,0,SEEK_END); //將文件指針置尾
- fileLen = ftell(cipher); //取文件指針當前位置
- rewind(cipher); //將文件指針重指向文件頭
- while(1){
- //密文的字節數一定是8的整數倍
- fread(cipherBlock,sizeof(char),8,cipher);
- DES_DecryptBlock(cipherBlock,subKeys,plainBlock);
- times += 8;
- if(times < fileLen){
- fwrite(plainBlock,sizeof(char),8,plain);
- }
- else{
- break;
- }
- }
- //判斷末尾是否被填充
- if(plainBlock[7] < 8){
- for(count = 8 - plainBlock[7]; count < 7; count++){
- if(plainBlock[count] != '\0'){
- break;
- }
- }
- }
- if(count == 7){//有填充
- fwrite(plainBlock,sizeof(char),8 - plainBlock[7],plain);
- }
- else{//無填充
- fwrite(plainBlock,sizeof(char),8,plain);
- }
- fclose(plain);
- fclose(cipher);
- return OK;
- }
最後,寫一個簡單的main函數來檢驗它:
- int main()
- {
- clock_t a,b;
- a = clock();
- DES_Encrypt("1.txt","key.txt","2.txt");
- b = clock();
- printf("加密消耗%d毫秒\n",b-a);
- system("pause");
- a = clock();
- DES_Decrypt("2.txt","key.txt","3.txt");
- b = clock();
- printf("解密消耗%d毫秒\n",b-a);
- getchar();
- return 0;
- }
運行結果就不重要了,自己去弄幾個文件放工程目錄下檢驗去吧。
至此,整個實現完成。該算法在1.79GHZ的CPU上測試的速度是850KB/S。不過大家別過分在代碼上追求速度,做到我以上提到的(捨棄動態內存分配)就足夠了,況且,這樣做也是在加密算法的程序並不複雜的情況下,如果是一個複雜的系統,那麼另當別論,更不必過分到連模塊化都不要,那樣的代碼只會讓人覺得醜陋,沒人願意維護。加密算法與CPU的運轉速度是成線性關係的。隨着雙核以及多核CPU的出現,硬件的改善講會成倍的加快算法的運行速度。