Rsa.java

import java.math.BigInteger;

public class Rsa {
    public static void main(String[] args) {
        BigInteger publicKey = new BigInteger(args[0]);
        BigInteger secretKey = new BigInteger(args[1]);
        BigInteger n = new BigInteger(args[2]);
        BigInteger m = new BigInteger(args[3]);
        
        BigInteger e = m.modPow(publicKey, n);
        System.out.println("Encrypted message: " + e);
        
        BigInteger d = e.modPow(secretKey, n);
        System.out.println("Decrypted message: " + d);
    }
}

RsaKeygen.java

import java.math.BigInteger;
import java.util.Random;

public class RsaKeygen {
    public static void main(String[] args) {
        Random r1 = new Random(System.currentTimeMillis());
        Random r2 = new Random(System.currentTimeMillis() * 10);
        
        int e = Integer.parseInt(args[0]);
        BigInteger p = BigInteger.probablePrime(32, r1);
        BigInteger q = BigInteger.probablePrime(32, r2);
        BigInteger n = p.multiply(q);
        
        BigInteger p1 = p.subtract(BigInteger.ONE);
        BigInteger q1 = q.subtract(BigInteger.ONE);
        BigInteger phi = p1.multiply(q1);
        
        while (true) {
            BigInteger gcd = phi.gcd(new BigInteger("" + e));
            if (gcd.equals(BigInteger.ONE)) break;
            
            e++;
        }
        
        BigInteger publicKey = new BigInteger("" + e);
        BigInteger secretKey = publicKey.modInverse(phi);
        
        System.out.println("Public key: " + publicKey + ", " + n);
        System.out.println("Secret key: " + secretKey + ", " + n);
    }
}