import java.util.ArrayList;
import java.util.List;
import java.math.BigInteger;
 
/**
 * Testing prime factor decryption
 *
 * @author Emmanuel
 */
public class Main {
 
    /**
     * Main method
     *
     * @param args command line arguments
     */
    public static void main(String[] args) {
        // private primes and totient
        BigInteger p1, p2, phi;
        p1 = new BigInteger("67");
        p2 = new BigInteger("23");
        phi = p1.subtract(BigInteger.ONE).multiply(p2.subtract(BigInteger.ONE));
        System.out.println("Prime 1: " + p1);
        System.out.println("Prime 2: " + p2);
        System.out.println("Euler's Totient: " + phi);
 
        // prime product (modulus) and public exponent
        BigInteger pp, ep;
        pp = p1.multiply(p2);
        //ep = new BigInteger("65537");
        BigInteger f = BigInteger.valueOf(2L);
        ep = coprime(phi, phi.divide(f).add(f));
        System.out.println("Modulus: " + pp);
        System.out.println("Public Exponent: " + ep);
        System.out.println("Private Exponent: " + ep.modInverse(phi));
 
        // test encryption
        for(int i = 1; i <= 100; i++) {
        	BigInteger c = BigInteger.valueOf((long) i);
        	System.out.println(i + " => " + c.modPow(ep, pp));
        }
    }
 
    /**
     * Calculate the next co-prime of number with minimum defined
     *
     * @param n the number to check for co-primes
     * @param i the minimum to start checking from
     * @return the next co-prime or NULL if none is found
     */
    private static BigInteger coprime(BigInteger n, BigInteger i) {
        for (; i.compareTo(n) < 0; i = i.add(BigInteger.ONE)) {
            if (i.gcd(n).equals(BigInteger.ONE)) {
                return i;
            }
        }
        return null;
    }
}
 

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