Hey guys
I have a finished RSA program. Using the BIGINTEGER methode
It can crypt and decrypt numbers, primes

I generated the primes with bigintegers built in function..
However Im asked to do the primes more properly using a rabbin miller test

Im supposed to generate x number of primes with x numer bitlength, 512,1024 etc
Also to generate 20 random "a" as a test

I cant post link so, search : wikipedia java miller, theres a pseduocode that works
, scroll down to Java

I get the mathematical operations done here, I know the Rabbin miller
but im not quite sure how to turn this into a prime generator
also how to generate 20 random a?

--- Update ---

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

public class MillerRabin {

private static final BigInteger ZERO = BigInteger.ZERO;
private static final BigInteger ONE = BigInteger.ONE;
private static final BigInteger TWO = new BigInteger("2");
private static final BigInteger THREE = new BigInteger("3");

public static boolean isProbablePrime(BigInteger n, int k) {
if (n.compareTo(ONE) == 0)
return false;
if (n.compareTo(THREE) < 0)
return true;
int s = 0;
BigInteger d = n.subtract(ONE);
while (d.mod(TWO).equals(ZERO)) {
d = d.divide(TWO);
for (int i = 0; i < k; i++) {
BigInteger a = uniformRandom(TWO, n.subtract(ONE));
BigInteger x = a.modPow(d, n);
if (x.equals(ONE) || x.equals(n.subtract(ONE)))
int r = 0;
for (; r < s; r++) {
x = x.modPow(TWO, n);
if (x.equals(ONE))
return false;
if (x.equals(n.subtract(ONE)))
if (r == s) // None of the steps made x equal n-1.
return false;
return true;

private static BigInteger uniformRandom(BigInteger bottom, BigInteger top) {
Random rnd = new Random();
BigInteger res;
do {
res = new BigInteger(top.bitLength(), rnd);
} while (res.compareTo(bottom) < 0 || res.compareTo(top) > 0);
return res;

public static void main(String[] args) {
// run with -ea to enable assertions
String[] primes = { "1", "3", "3613", "7297",
"226673591177742970257407", "2932031007403" };
String[] nonPrimes = { "3341", "2932021007403",
"226673591177742970257405" };
int k = 40;
for (String p : primes)
assert isProbablePrime(new BigInteger(p), k);
for (String n : nonPrimes)
assert !isProbablePrime(new BigInteger(n), k);

EDIT: Posted the code from wikipedia
the ending string thing and top bottom thing I assume I can skip
The mathematical operations for rabbin implemented in java, I can use them

So create 20 random A, generate x number of primes of x bits
and print two primes p and q to use for my rsa program

Im gonna have the programs separatley