C - Programming Guide

C/C++ Program to implement RSA Algorithm

#include<iostream.h>
#include<conio.h>
#include<math.h>

int main()
{
   int i,j,k,p,q,flag,e,x,d;
   clrscr();
  cout<<"\n Enter Value of p :: ";
  cin>>p;
  cout<<"\n Enter Value of q :: ";
  cin>>q;
  int n=p*q;
  int fn=(p-1)*(q-1);

  cout<<"\n Value of (p,q) :: "<<p<<" "<<q;
  cout<<"\n Value of n,fn  :: "<<n<<" "<<fn;
  cout<<"\n\n Select Public Key e (1 < e < "<<fn<<") ::";
  cin>>e;

  int sk;
  for(i=1;i>0;i++)
  {
    x=i*e;
    d=x%fn;
    if(d==1)
    {
    cout<<"\n\n Private Key ::"<<i;
    sk=i;
    break;
    }

  }

  int pt;
  cout<<"\n\n  Enter Plain Text ::";
  cin>>pt;

  int m=1;
  for(i=0;i<e;i++)
    m=(m*pt)%n;
  m=m%n;
  cout<<"\n\n  Cipher Text ::"<<m;
  getch();

  k=1;
  for(i=0;i<sk;i++)
    k=(k*m)%n;
  k=k%n;
  cout<<"\n\n  Decrypted Text ::"<<k;
  getch();
 return 0;
}