DES算法

程序员文章站 2022-05-15 14:58:44

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DES算法

DES算法

算法原理概述

DES(Data Encryption Standard)算法为密码*中的对称密码*，又被称为美国数据加密标准，是1972年美国IBM公司研制的对称密码*加密算法。明文按64位进行分组，**长64位，**事实上是56位参与DES运算（第8、16、24、32、40、48、56、64位是校验位，使得每个**都有奇数个1）分组后的明文组和56位的**按位替代或交换的方法形成密文组的加密方法。
其入口参数有三个：key、data、mode。key为加密解密使用的**，data为加密解密的数据，mode为其工作模式。当模式为加密模式时，明文按照64位进行分组，形成明文组，key用于对数据加密，当模式为解密模式时，key用于对数据解密。实际运用中，**只用到了64位中的56位，这样才具有高的安全性。

总体结构

加密过程

DES算法

对64位明文进行初始置换（IP_Transform）

将IP置换后的64位数据分为两部分，左32位记为L，右32位记为R

去掉奇偶校验位的**为56位（PC1_Transform），将其左右分为28位，分别将左右28位进行循环左移位（shift_left）再合并为56位，再经压缩（PC2_Transform）后为48位子**（GenerateSubKey）

对R进行扩展置换（E_Transform），得到48位的数据与**压缩后的48位异或

将经过异或后的48位数据分为8组，每组6位放入S盒中，输出8组4位，总共为32位（SBOX），再经过（P_Transform）

将上面得到的32位数据与L异或结果赋给R

前15次依次交换L和R位置（Swap）

重复以上2-7过程16次

将最后的到的L和R合并做逆置换（IP_1_Transform）

解密过程

与加密过程一样，只是每次迭代使用左移**的时候是使用对称的，也就是加密是第i轮，则解密使用第17-i轮。

模块分解

将每次位数置换变换，异或，交换，字节位转换和加密解密分为一个模块

    void CharToBit(char ch[8],char bit[64]);
    void BitToChar(char bit[64],char ch[8]);
    void GenerateSubKey(char key[64],char subKeys[16][48]);
    void PC1_Transform(char key[64], char tempbts[56]);
    void PC2_Transform(char key[56], char tempbts[48]);
    void Shift_Left(char data[56], int time);
    void IP_Transform(char data[64]);
    void IP_1_Transform(char data[64]);
    void E_Transform(char data[48]);
    void P_Transform(char data[32]);
    void SBOX(char data[48]);
    void XOR(char R[48], char L[48], int count);
    void Swap(char left[32],char right[32]);
    void Encrypt64Bit(char plainBlock[8], char subKeys[16][48], char cipherBlock[8]);
    void Decrypt64Bit(char cipherBlock[8], char subKeys[16][48], char plainBlock[8]);
    void Encrypt(char *plainFile, char *keyStr,char *cipherFile);
    void Decrypt(char *cipherFile, char *keyStr,char *plainFile);

IP置换

    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
    };

表的意思就是第一次变换时，第57位移到第1位，第49位移到第2位，…… 依此类推。得到64位数据

**变换

    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
    };
    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
    };
    //左移次数的规定
    int MOVE_TIMES[16] = {1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};

**经PC_1变换去奇偶校验位后由64位变为56位，再经过PC_2压缩变为48位，分别对左右28位在第i次迭代中使用上述对应的移动次数。

扩展置换

    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
    };

扩展置换是将R由32位扩展为48位。

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}}};

使用S[i]替换R与K1异或结的果B[i][6]。过程如下: 取出B[i][6]的第1位和第6位连成一个2位数m， m就是S[i]中对应的行数(0-3)，取出B[i][6]的第2到第5位连成一个4位数n(0-15)，n就是S[i]中对应的列数，用S[i][m][n]代替B[i][6]。S是4行16列的对应表，里面是4位的数，一共有8个S。

P置换

    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
    };

P置换是将经过S-盒后的32位数据再经一个置换。

IP逆置换

    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
    };

数据结构

采用char的数据结构来存储输入明文以及保存的密文和其每个位。通过读取两个txt文本文件，要加密的plain.txt和**key.txt。加密输出为密文，解密输出解密后的明文。

C++类代码实现

源代码

des.h

class DES {
  private:
    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
    }; 
    //逆初始置换表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
    };

    //扩充置换表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
    };

    //置换函数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}}};
    //置换选择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
    };

    //置换选择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
    };

    //对左移次数的规定
    int MOVE_TIMES[16] = {1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};

  public:
    DES();
    ~DES();
    void CharToBit(char ch[8],char bit[64]);
    void BitToChar(char bit[64],char ch[8]);
    void GenerateSubKey(char key[64],char subKeys[16][48]);
    void PC1_Transform(char key[64], char tempbts[56]);
    void PC2_Transform(char key[56], char tempbts[48]);
    void Shift_Left(char data[56], int time);
    void IP_Transform(char data[64]);
    void IP_1_Transform(char data[64]);
    void E_Transform(char data[48]);
    void P_Transform(char data[32]);
    void SBOX(char data[48]);
    void XOR(char R[48], char L[48], int count);
    void Swap(char left[32],char right[32]);
    void Encrypt64Bit(char plainBlock[8], char subKeys[16][48], char cipherBlock[8]);
    void Decrypt64Bit(char cipherBlock[8], char subKeys[16][48], char plainBlock[8]);
    void Encrypt(char *plainFile, char *keyStr,char *cipherFile);
    void Decrypt(char *cipherFile, char *keyStr,char *plainFile);  
};

Des.cpp

#include "des.h"
#include <iostream>
#include <fstream>
#include <bitset>
#include <cstring>
using namespace std;

DES::DES() {}
DES::~DES() {}

void DES::IP_Transform(char data[64]) {
  char temp[64];
  for(int i = 0; i < 64; i++) {
    temp[i] = data[IP_Table[i]];
  }
  memcpy(data,temp,64);
}

void DES::GenerateSubKey(char key[64], char subKeys[16][48]) {
  char temp[56];
  PC1_Transform(key,temp);
  for(int i = 0; i < 16; i++) {
    Shift_Left(temp, MOVE_TIMES[i]);
    PC2_Transform(temp, subKeys[i]);
  }
}

void DES::PC1_Transform(char key[64], char tempbts[56]) {
  for(int i = 0; i < 56; i++) {
    tempbts[i] = key[PC_1[i]];
  }
}

void DES::PC2_Transform(char key[56], char tempbts[48]) {
  for(int i = 0; i < 48; i++) {
    tempbts[i] = key[PC_2[i]];
  }
}

void DES::Shift_Left(char data[56], int time){    
  char temp[56];
  memcpy(temp,data,time);
  memcpy(temp+time,data+28,time);
  memcpy(data,data+time,28-time);
  memcpy(data+28-time,temp,time);

  memcpy(data+28,data+28+time,28-time);
  memcpy(data+56-time,temp+time,time);    

}

void DES::IP_1_Transform(char data[64]) {
  char temp[64];
  for(int i = 0; i < 64; i++) {
    temp[i] = data[IP_1_Table[i]];
  }
  memcpy(data,temp,64);
}

void DES::E_Transform(char data[48]) {
  char temp[48];
  for(int i = 0; i < 48; i++) {
    temp[i] = data[E_Table[i]];
  }
  memcpy(data,temp,48);
}

void DES::P_Transform(char data[32]) {
  char temp[32];
  for(int i = 0; i < 32; i++) {
    temp[i] = data[P_Table[i]];
  }
  memcpy(data,temp,32);
}

void DES::XOR(char R[48], char L[48] ,int count) {
  for(int i = 0; i < count; i++) {
    R[i] ^= L[i];
  }
}

void DES::SBOX(char data[48]) {
  int line,row,output;
  int cur1,cur2;
  for(int i = 0; i < 8; i++){
    cur1 = i * 6;
    cur2 = i<< 2;

    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[i][line][row];

    data[cur2] = (output&0X08)>>3;
    data[cur2+1] = (output&0X04)>>2;
    data[cur2+2] = (output&0X02)>>1;
    data[cur2+3] = output&0x01;
  }
}

void DES::Swap(char left[32], char right[32]) {
  char temp[32];
  memcpy(temp,left,32);    
  memcpy(left,right,32);    
  memcpy(right,temp,32);
}

void DES::CharToBit(char ch[8],char bit[64]){
  for(int i = 0; i < 8; i++) {
    for (int j = 0; j < 8; j++) {
      *(bit + i * 8 + j) = (ch[i]>> j) & 1;
    }
  }
}

void DES::BitToChar(char bit[64],char ch[8]){
  memset(ch, 0, 8);
  for(int i = 0; i < 8; i++) {
    for (int j = 0; j < 8; j++) {
      *(ch + i) |= bit[i * 8 + j]<< j;
    }
  }
}

void DES::Encrypt64Bit(char plainBlock[8], char subKeys[16][48], char cipherBlock[8]){
  char plainBits[64];
  char copyRight[48];
  int i;

  CharToBit(plainBlock,plainBits);        
  IP_Transform(plainBits);

  for(i = 0; i < 16; i++){        
    memcpy(copyRight,plainBits+32,32);
    E_Transform(copyRight);
    XOR(copyRight,subKeys[i],48);    
    SBOX(copyRight);
    P_Transform(copyRight);
    XOR(plainBits,copyRight,32);
    if(i != 15){
      Swap(plainBits,plainBits+32);
    }
  }
  IP_1_Transform(plainBits);
  BitToChar(plainBits,cipherBlock);
}

void DES::Decrypt64Bit(char cipherBlock[8], char subKeys[16][48],char plainBlock[8]){
  char cipherBits[64];
  char copyRight[48];

  CharToBit(cipherBlock,cipherBits);        
  IP_Transform(cipherBits);

  for(int i = 15; i >= 0; i--){        
    memcpy(copyRight,cipherBits+32,32);
    E_Transform(copyRight);
    XOR(copyRight,subKeys[i],48);        
    SBOX(copyRight);
    P_Transform(copyRight);        
    XOR(cipherBits,copyRight,32);
    if(i != 0) {
      Swap(cipherBits,cipherBits+32);
    }
  }
  IP_1_Transform(cipherBits);
  BitToChar(cipherBits,plainBlock);
}

void DES::Encrypt(char *plainFile, char *keyStr,char *cipherFile){
  FILE *plain,*cipher;
  int count;
  char plainBlock[8],cipherBlock[8],keyBlock[8];
  char bKey[64];
  char subKeys[16][48];
  if((plain = fopen(plainFile,"rb")) == NULL){
    cout<< "read error"<<endl;
    return;
  }    
  if((cipher = fopen(cipherFile,"wb")) == NULL){
    cout<< "write error"<< endl;
    return;
  }
  memcpy(keyBlock,keyStr,8);
  CharToBit(keyBlock,bKey);
  GenerateSubKey(bKey,subKeys);

  while(!feof(plain)){
    if((count = fread(plainBlock, sizeof(char), 8, plain)) == 8){
      Encrypt64Bit(plainBlock, subKeys, cipherBlock);
      fwrite(cipherBlock, sizeof(char), 8, cipher);    
    }
  }
  if(count){//不足8位时填充
    memset(plainBlock + count,'\0', 7 - count);
    plainBlock[7] = 8 - count;
    Encrypt64Bit(plainBlock,subKeys,cipherBlock);
    fwrite(cipherBlock, sizeof(char), 8, cipher);
  }
  fclose(plain);
  fclose(cipher);
}

void DES::Decrypt(char *cipherFile, char *keyStr,char *plainFile){
  FILE *plain, *cipher;
  int count,times = 0;
  long fileLen;
  char plainBlock[8], cipherBlock[8], keyBlock[8];
  char bKey[64];
  char subKeys[16][48];
  if((cipher = fopen(cipherFile,"rb")) == NULL){
    cout<< "read error"<< endl;
    return;
  }
  if((plain = fopen(plainFile,"wb")) == NULL){
    cout<< "write error"<< endl;
    return;
  }
  memcpy(keyBlock,keyStr,8);
  CharToBit(keyBlock,bKey);
  GenerateSubKey(bKey,subKeys); 
  fseek(cipher, 0, SEEK_END);    //将文件指针置尾
  fileLen = ftell(cipher);    //取文件指针当前位置
  rewind(cipher);                //将文件指针重指向文件头
  while(1){
    fread(cipherBlock,sizeof(char), 8, cipher);
    Decrypt64Bit(cipherBlock, subKeys, plainBlock);                        
    times += 8;
    if(times < fileLen){
      fwrite(plainBlock, sizeof(char), 8, plain);
    } else {
      break;
    }
  }
  if(plainBlock[7] < 8) {
    for(count = 8 - plainBlock[7]; count < 7; count++){
      if(plainBlock[count] != '\0'){
        break;
      }
    }
  }    
  if(count == 7) {
    fwrite(plainBlock, sizeof(char), 8 - plainBlock[7], plain);
  } else {
    fwrite(plainBlock, sizeof(char), 8, plain);
  }
  fclose(plain);
  fclose(cipher);
}

int main() {
  DES d;
  d.Encrypt("plain.txt","key.txt","cipher.txt");
  d.Decrypt("cipher.txt","key.txt","newplain.txt");  
  return 0;  
}

测试结果

输入key.txt
yes
输入plain.txt
helloworld
加密输出cipher.txt
鬣aaa@qq.com喯E絟l亖
解密输出newplain.txt
helloworld

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DES算法

DES算法

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解密过程

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