V5307. OWASP. Potentially predictable seed is used in pseudo-random number generator.

The analyzer has detected cases where a pseudo-random number generator is used. It may result in insufficient randomness or predictability of the generated number.

Case 1

A new object of the 'Random' type is created every time when a random value is required. This is inefficient and may result in creating numbers that are not random enough depending on the JDK.

Look at an example:

public void test() {
  Random rnd = new Random();
}

For better efficiency and a more random distribution, create an instance of the 'Random' class, save and reuse it.

static Random rnd = new Random();

public void test() {
  int i = rnd.nextInt();
}

Case 2

The analyzer has detected a suspicious code that initializes the pseudo-random number generator with a constant value.

public void test() {
  Random rnd = new Random(4040);
}

Generated numbers are predictable. They are repeated every time the program runs. To avoid this, do not use a constant number. The developers may have used the current system time instead:

static Random rnd = new Random(System.currentTimeMillis());

public void test() {
  int i = rnd.nextInt();
}

This diagnostic is classified as: