Thread: RSA algo not working. (algoritm included)... not working for some numbers..[TOMORROW EXAMS]

for example: not working when prime nos are 7 and 13.. and when data is 36.

/* Algorithm:
    Choose p = 3 and q = 11
    Compute n = p * q = 3 * 11 = 33
    Compute f(n) = (p - 1) * (q - 1) = 2 * 10 = 20
    Choose e such that 1 < e < f(n) and e and n are coprime. Let e = 7
    Compute a value for d such that (d * e) % f(n) = 1. One solution is d = 3 [(3 * 7) % 20 = 1]
    Public key is (e, n) => (7, 33)
    Private key is (d, n) => (3, 33)
    The encryption of m = 2 is c = 27 % 33 = 29
    The decryption of c = 29 is m = 293 % 33 = 2
*/
import java.io.*;
 
public class RSA
{
  public static void main(String args[]) throws IOException
  {
     BufferedReader buff=new BufferedReader(new InputStreamReader(System.in));
     System.out.println("Enter 1st prime nos:");
     int p=Integer.parseInt(buff.readLine());
     System.out.println("Enter 2nd prime nos:");
     int q=Integer.parseInt(buff.readLine());
     //prime
     boolean flag=true;
     boolean p_true=check(p,flag);     
     boolean q_true=check(q,flag);
     if((p_true==true) && (q_true==true))
        {
           System.out.println("Nos are prime");
        }
    else
        {
           System.out.println("Nos are not prime");
        }
 
 
     int n=p*q;
     int N=((p-1)*(q-1));
     int e=2;
     for(int i=2;i<N;i++)      
        {
           if((N%i)!=0)
             {e=i;break;}
           else
              {continue;
               }            
        }System.out.println("e="+e);
 
 
 
 
       int d;
       for(int i=1;;i++)
         {
           if(((i*e)%N)==1)
             { d=i;
              break;}
           else continue; 
         }
       System.out.println("d="+d);
 
 
     System.out.println("Enter data to be encrypted");
     int data=Integer.parseInt(buff.readLine());
     int encrypt_data=(((int)Math.pow(data,e))%n);
      System.out.println("encrypted data"+encrypt_data);
     int decrypt_data=(((int)Math.pow(encrypt_data,d))%n);
      System.out.println("decrypted data"+decrypt_data);
}
     public static boolean check(int p, boolean flag)
        { flag=true;
           for(int i=2;i<p;i++)
             {
                if(p%i!=0)
                  continue;
                else 
                {flag=false;
                break;}
             }return flag;
        }
}

Input- Two prime numbers which is used to first encrypt and then data given:
in above case, 7 and 13 were prime numbers, data was 36
Output- the output shows the encrypted and decrypted data.

but still it doent work for prime numbers : 7 and 5. data:65

nothing wrong when you executed it. but the problem is, its working only for limited numbers.

i think it should work because it is an standard algorithm developed by Rivest, Adelman. Google it.

[output]C:\Users\Ra\Desktop>java RSA
Enter 1st prime nos:
7
Enter 2nd prime nos:
13
Nos are prime
e=5
d=29
Enter data to be encrypted
65
encrypted data39
decrypted data36
[/output]

That is working. My mistake. Sorry.