//        //  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;        }