RSA Implementation

[Heartstrings]

Hi, this is an RSA algorithm implementation in c++. The code runs fine but whenever I included a space in the message to be encrypted, when it decrypts, the space is replaced with a C. Why is this?

#include<iostream>
#include<cmath>
#include<cstdio>

using namespace std;

class RSA
{
       public:
              long int p,q,n,t,flag,e[100],d[100],temp[100],j,m[100],en[100],i;
              string msg;
              RSA(long x, long y, string s)
              {
                     long i;
                     p = x;
                     q = y;
                     msg = s;
                     n=p*q;
                     t=(p-1)*(q-1);
                     for(i=0;i<msg.size();i++)
                     {
                           m[i] = msg[i];
                     }
              }
             
              int prime(long pr)
              {
                     int i;
                     j=sqrt(pr);
                     for (i=2;i<=j;i++) {
                           if(pr%i==0)
                               return 0;
                     }
                     return 1;
              }
              void ce()
              {
                     int k;
                     k=0;
                     for (i=2;i<t;i++)
                     {
                           if(t%i==0)
                               continue;
                           flag=prime(i);
                           if( flag==1 && i!=p && i!=q)
                           {
                                  e[k]=i;
                                  flag=cd(e[k]);
                                  if(flag>0) {
                                         d[k]=flag;
                                         k++;
                                  }
                                  if(k==99)
                                          break;
                           }
                     }
                     for (i=0;i<j-1;i++)
                     {
                           cout<<(i+1)<<"\t("<<e[i]<<","<<d[i]<<")"<<endl;
                     }
                     cout<<endl;
              }
              long int cd(long int x)
              {
                     long int k=1;
                     while(1) {
                           k=k+t;
                           if(k%x==0)
                               return(k/x);
                     }
              }
              void encrypt(int x)
              {
                     long int pt,ct,key=e[x-1],k,len;
                     cout<<"Value of e used is "<<key<<endl;
                     i=0;
                     len = msg.size();
                     while(i!=len)
                     {
                           pt=m[i];
                           pt=pt-96;
                           k=1;
                           for (j=0;j<key;j++)
                           {
                                  k=k*pt;
                                  k=k%n;
                           }
                           temp[i]=k;
                           ct=k+96;
                           en[i]=ct;
                           i++;
                     }
                     en[i]=-1;
                     cout<<"The Encrypted Message : "<<endl;
                     for (i=0;en[i]!=-1;i++)
                     cout<<(char)en[i];
                     cout<<endl;
              }
              void decrypt(int x)
              {
                     long int pt,ct,key=d[x-1],k;
                     cout<<"Value of d used is "<<key<<endl;
                     i=0;
                     while(en[i]!=-1)
                     {
                           ct=temp[i];
                           k=1;
                           for (j=0;j<key;j++) {
                                  k=k*ct;
                                  k=k%n;
                           }
                           pt=k+96;
                           m[i]=pt;
                           i++;
                     }
                     m[i]=-1;
                     cout<<"The Decrypted Message : "<<endl;
                     for (i=0;m[i]!=-1;i++)
                     cout<<(char)m[i];
                     cout<<endl;
              }
};


int main()
{
       long i,n,t,p,q,x;
       cout<<"Enter the Prime Numbers P & Q"<<endl;
       cin>>p>>q;
       cout<<"Enter the Message"<<endl;
       string msg;
       getchar();
       getline(cin,msg);
       RSA ob(p,q,msg);
       cout<<"Possible values of (e,d) are"<<endl;
       ob.ce();
       cout<<"Chose which values of (e,d) you want to use?"<<endl;
       cin>>x;
       cout<<endl;
       ob.encrypt(x);
       cout<<endl;
       ob.decrypt(x);
       return 0;
}

Thanks. Also if you have any tips to help me modify this to make it read from a text file and then decrypt to a new file, let me know!

[2kaud]

What debugging of the code has been done by stepping through the code with the debugger to see where the execution deviates from that expected?

PS It looks like an issue is with the prime numbers. If they both are > 10 then it seems to work, but if one is < 10 then it seems not to.

There is also a buffer overflow problem if the entered message has more than 99 characters.