affine-caesar.rar_MOD_affine cipher_加密解密affine

// affine caesar.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include <iostream> using namespace std; int a,b; //define a and b char p,c; //define plaintext p, and cipher text c int input1() //input for encryption { cout<<"Input a:"; cin>>a; cout<<"Input b:"; cin>>b; cout<<"Input plaintext p:"; cin>>p; return 0; } int input2() //input for decryption { cout<<"Input a:"; cin>>a; cout<<"Input b:"; cin>>b; cout<<"Input ciphertext c:"; cin>>c; return 0; } int encrypt(int a, int b, char p) //Encryption function { int pp=p-97; //change letter into number int cc; //define cipher number cc=(a*pp+b)%26; //function: C=[a,b],p=(a*p+b) mod 26 cc=cc+97; char c= (char)cc; //change cipher number to cipher letter cout<<"Cipher text is: "<<c<<endl; //output cipher text return c; } int decrypt(int a, int b, char c) //Decryption function { int cc=c-97; //chage letter into number int aa=0, r=0; do //find inverse a=aa { aa=aa+1; r=(a*aa) %26; }while(r!=1); int pp; //define plaintext number pp=(aa*(cc-b+26))% 26; //function: p=a^-1*(C-b) mod 26 pp=pp+97; char p= (char)pp; //change plaintext number into plaintext letter cout<<"Plaintext p is: "<<p; //output plaintext return p; } int choose() //choose funtions { cout<<"a. Encryption. \nb. Decryption.\n"; char input=1; cout<<"Input: "; cin>>input; cout<<endl; switch (input) { case 'a': { input1(); encrypt(a,b,p); cout<<endl<<endl; break; } case 'b': { input2(); decrypt(a,b,c); cout<<endl<<endl; break; } default:cout<<"Error Input! Try again!"<<endl;break; } return 0; } int _tmain(int argc, _TCHAR* argv[]) //main function { int rr=1; do{ choose(); }while(rr==1); return 0; }