在JAVA中的cicle中生成变量期间，程序会冻结

Question

In my school, teachers told has to write a program that encrypts a number with the RSA encryption. The whole program works just fine, except for a small part, that sometimes freezes the program when gets executed. Here's the code of the class:

package newpackage;

import java.lang.Math.*;
import java.util.*;
import java.lang.*;
import java.io.*;

public class CrittografiaRSA {
    public static Random rand = new Random();
    public static double d;
    public static String cod;
    public static int e;

    public static boolean EuclideAlgorithm(int a, int b) {
        int r;
        boolean k = false;
        while (b != 0) {
            r = a % b;
            a = b;
            b = r;

        }
        if (a == 1) {
            k = true;
        }
        if (a != 1) {
            k = false;
        }
        return k;
    }


    public static String RSA(int p, int q, String mex, int e) {
        CrittografiaRSA.cod = "";
        int pqless, n, i = 0, v;
        boolean GCD = false, dVerify = false, PQPN;

        PQPN = EuclideAlgorithm(p, q);

        if (PQPN == false) {
            cod = "P e Q non sono primi fra loro";
            return cod;
        }

        n = p * q;
        pqless = (q - 1) * (p - 1);

        if (NewJFrame.generateE == true) {
            while (GCD == false || e >= pqless || e == 1) {
                e = rand.nextInt(pqless);
                System.out.println(e);
                GCD = EuclideAlgorithm(e, pqless);
            }
        }

        if (NewJFrame.generateE == false) {
            GCD = EuclideAlgorithm(e, pqless);
            if (GCD == false || e >= pqless || e == 1) {
                cod = "La E fornita non è adatta.";
                return cod;
            }
        }
        CrittografiaRSA.d = e;
        while (e == CrittografiaRSA.d || d == 0) {

            while (dVerify == false) {
                CrittografiaRSA.d = ((i * pqless) + 1) / (double) e;
                v = (int) d;
                if (d == v) {
                    dVerify = true;
                }
                i = i + 1;
            }
            if (e == i && NewJFrame.generateE == false) {
                cod = "Nessuna chiave D generabile con le chiavi inserite";
                return cod;
            }
        }

        System.out.println("La chiave pubblica è: (" + n + "," + e + ")\n" + "La chiave privata è: (" + n + "," + (int) d + ")");
        if (NewJFrame.cryptoChar == false) {

            int mexx = Integer.parseInt(mex);
            if (n <= mexx) {
                cod = "Messaggio troppo grande per le chiavi fornite";
                return cod;
            }

            long c;
            double pot = Math.pow(mexx, e);
            c = (long) (pot % n);
            CrittografiaRSA.cod = Long.toString(c);

        }


        return CrittografiaRSA.cod;
    }
}

In particular, the program freezes right here:

    if(NewJFrame.generateE==true){
        while(GCD == false || e>=pqless || e==1){
            e = rand.nextInt(pqless);
            System.out.println(e);
            GCD = EuclideAlgorithm(e, pqless);
        }
    }

I noticed, however, that the smaller are p and q, the higher are the chances of to bug.

Hope the code is understandable, I removed the italian comments 'cause IDK if the whole code is really necessary, but whatever. Thanks for helping me.

Answer 1

while(b != 0)
{
     r = a % b;
     a = b; 
     b = r;
     System.out.println(b); // add this
}

Is application still freezing after this modification?

Answer 2

If p or q are equal to 1 then e will always be equal to pqless because rand.nextInt(pqless) generates a random number between 0 and pqless . With a value of 1 for p and/or q , pqless = 0 so e = 0 . Thus, the infinite loop begins.

pqless = (q - 1) * (p - 1);

    if (NewJFrame.generateE == true) {
        while (GCD == false || e >= pqless || e == 1) {
            e = rand.nextInt(pqless);
            System.out.println(e);
            GCD = EuclideAlgorithm(e, pqless);
        }
    }