How to use jsbn

function biggestPowerOfTwo(num) {
 if (num.compareTo(zero) === 0) return zero;
 const power = bigint(String(num.toString(2).length - 1));
 return two.pow(power);
}

function generateSecretKey(session, packet) {
  const cipherPublicKey = packet.readString();
  const sharedKey = HabboEncryption.calculateDiffieHellmanSharedKey(cipherPublicKey);
  
  if (sharedKey.equals(BigInteger.ZERO)) {
    return;
  }
  
  session.enableRC4(sharedKey.toByteArray());
  session.sendPacket(new CompleteDiffieHandshakeComposer(HabboEncryption.PublicKey.toString()));
}

function calculateDiffieHellmanSharedKey(cipherKey) {
  const publicKey = Rsa.decrypt(cipherKey);
  const publicClientKey = new BigInteger(publicKey, 10);
  return publicClientKey.modPow(Rsa.d, prime);
}

for (;;) {
  this.p = new BigInteger(B - qs, 1, rng);
  if (this.p.subtract(BigInteger.ONE)
    .gcd(ee)
    .compareTo(BigInteger.ONE) == 0 && this.p.isProbablePrime(10)) break
  if (this.q.subtract(BigInteger.ONE)
    .gcd(ee)
    .compareTo(BigInteger.ONE) == 0 && this.q.isProbablePrime(10)) break
  this.q = t
var p1 = this.p.subtract(BigInteger.ONE);
var q1 = this.q.subtract(BigInteger.ONE);
var phi = p1.multiply(q1);
if (phi.gcd(ee)
  .compareTo(BigInteger.ONE) == 0) {
  this.n = this.p.multiply(this.q);
  this.d = ee.modInverse(phi);
  this.dmp1 = this.d.mod(p1);
  this.dmq1 = this.d.mod(q1);

biggest = biggest.divide(two);
start = part.end.divide(biggest).subtract(one).multiply(biggest);