//  
    //  main.cpp  
    //  RSA  
    //  
    //  Created by liujan on 10/21/14.  
    //  Copyright (c) 2014 liujan. All rights reserved.  
    //  
      
    #include <iostream>  
    #include "cmath"  
    using namespace std;  
      
    long long p = 1949, q = 3413;  
    long long N = p * q;  
    long long e = 13007, d = 511;  
      
    //对a的b次幂取模 m（大数取模）  
    long long Mod(long long a, long long  b, long long m){  
        long long r = 1;  
        for (long long j = 0; j < b; j++){  
            r = (r * a) % m;  
              
        }  
        return r;  
    }  
      
    //对输入信息进行rsa编码  
    long long * rsaEncode(string message){  
        size_t length = message.length();  
        long long *ascii = new long long[length]; //存储信息的每个字符  
        long long *code = new long long[length];  //存储每个字符的rsa编码  
        for (size_t i = 0; i < length; i++){  
            ascii[i] = message[i];  
        }  
       
        for (size_t i = 0; i < length; i++){  
            code[i] = Mod(ascii[i], e, N ); //C=M^e (modN)  
        }  
          
        return code;  
    }  
      
    //根据rsa编码得到原来的信息  
    string rsaDecode(long long code[], size_t n){  
        long long  *ascii = new long long[n];  
        string message = "";  
        for (size_t i = 0; i < n; i++){  
            ascii[i] = Mod(code[i], d, N); //M=C^d (modN)  
            message += ((char)(ascii[i]));  
        }  
        return message;  
    }  
      
    int main(int argc, const char * argv[]) {  
        string message = "Hello World!";  
        size_t length = message.length();  
        long long *a = rsaEncode(message);  
          
          
        string newmessage = rsaDecode(a, length);  
        cout << newmessage << endl;  
          
        return 0;  
    }