Several classical cryptographic algorithms

Classical cryptography can be divided into two types: replace password (also called shift password) and replace password (also called transposition password). Typical replace passwords include Caesar passwords and affine transformations, the replacement password includes single-Table replacement and multi-Table replacement.

The following describes the implementation of several common classical cryptographic algorithms.

1. Caesar Password

void encrypt(char* text,int k,char cipher[1024]){int a[26];int A[26];int m;for(int i=97;i<123;i++){a[i-97]=i;A[i-97]=i-32;}int len=strlen(text);for(int j=0;j<len;j++){int t=text[j];if(96<t&&t<123){m=(text[j]+k-97)%26;cipher[j]=a[m];}else if(64<t&&t<91){m=(text[j]+k-65)%26;cipher[j]=A[m];}elsecipher[j]=' ';}}void decrypt(char* cipher,int k,char text[1024]){int a[26];int A[26];int m;for(int i=97;i<123;i++){a[i-97]=i;A[i-97]=i-32;}int len=strlen(cipher);for(int i=0;i<len;i++){int t=cipher[i];if(96<t&&t<123){m=(cipher[i]-k-71)%26;text[i]=a[m];}else if(64<t&&t<91){m=(cipher[i]-k-39)%26;text[i]=A[m];}elsetext[i]=' ';}}

2. Single Table replacement

//#include "Ceasar.h"#include "stdafx.h"void transkey(char* key,char table[27]){char tem[100]={0};char table1[30]={0};for(int i=97;i<123;i++)table1[i-97]=i;int len1=strlen(key);strcpy(tem,key);strcpy(tem+len1,table1);int len=strlen(tem);int k=1;int flag;if(isupper(tem[0]))tem[0]+=32;table[0]=tem[0];for(int i=1;i<strlen(tem)&&k<26;i++){if(!isalpha(tem[i]))continue;if(isupper(tem[i]))tem[i]+=32;flag=0;for(int j=0;j<k;j++){if(table[j]==tem[i]){flag=1;break;}}if(!flag)table[k++]=tem[i];}}void encrypt(char* text,char* key,char cipher[1024]){char table[27]={0};transkey(key,table);int len=strlen(text);for(int i=0;i<len;i++){if(!isalpha(text[i]))cipher[i]=text[i];else if(islower(text[i]))cipher[i]=table[text[i]-97];elsecipher[i]=table[text[i]-65]-32;}}void ttable(char table[27]){char ip[30]={0};for(int i=97;i<122;i++){ip[table[i-97]-'a']=i;}memcpy(table,ip,26);}void decrypt(char* cipher,char* key,char text[1024]){char table[27]={0};transkey(key,table);ttable(table);int len=strlen(cipher);for(int i=0;i<len;i++){if(!isalpha(cipher[i]))text[i]=cipher[i];else if(islower(cipher[i]))text[i]=table[cipher[i]-97];elsetext[i]=table[cipher[i]-65]-32;}}

3. Affine Transformation

//#include "Ceasar.h"#include "stdafx.h"void encrypt(char* text,int k1,int k2,char cipher[1024]){int len=strlen(text);int e=0;for(int j=0;j<len;j++){if(!isalpha(text[j])){cipher[j]=text[j];}else if(islower(text[j])){e=text[j]-'a';cipher[j] = (e*k1+k2) % 26 + 'a';}else{e=text[j]-'A';cipher[j] = (e*k1+k2) % 26 + 'A';}}}int rec(int k,int m){int i=1;int j=0;while(1){for(j=0;k*j<m*i+1;j++){}if(k*j==m*i+1)break;elsei++;}return j;}void decrypt(char* cipher,int k1,int k2,char text[1024]){int len=strlen(cipher);int  e=0;int k3=rec(k1,26);for(int i=0;i<len;i++){if(!isalpha(cipher[i])){text[i]=cipher[i];}else if(islower(cipher[i])){e=cipher[i]-'a';text[i] = (k3*(e-k2+26))% 26 + 'a';}else{   e = cipher[i] - 'A';text[i]=((e-k2+26)*k3)% 26 +'A';}}}

4. Virginia Password

//#include "Ceasar.h"#include "stdafx.h"void encrypt(char* text,char* key,char cipher[1024]){int len=strlen(text);int lenkey=strlen(key);for(int j=0;j<lenkey;j++)//keyСдif(isupper(key[j]))key[j]+=32;for(int i=0;i<len;i++){if(!isalpha(text[i]))cipher[i]=text[i];else if(isupper(text[i]))cipher[i]=(text[i]-'A'+key[i%lenkey]-'a')%26+'A';elsecipher[i]=(text[i]-'a'+key[i%lenkey]-'a')%26+'a';}}void decrypt(char* cipher,char* key,char text[1024]){int len=strlen(cipher);int lenkey=strlen(key);for(int j=0;j<lenkey;j++)//keyСдif(isupper(key[j]))key[j]+=32;for(int i=0;i<len;i++){if(!isalpha(cipher[i]))text[i]=cipher[i];else if(isupper(cipher[i]))text[i]=(26+cipher[i]-'A'-(key[i%lenkey]-'a'))%26+'A';elsetext[i]=(26+cipher[i]-'a'-(key[i%lenkey]-'a'))%26+'a';}}