Page History

...

import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;
// ...

public static void main (String args[]) {
   try {
     SecureRandom number = SecureRandom.getInstance("SHA1PRNG");
     // Generate 20 integers 0..20
     for (int i = 0; i < 20; i++) {
       System.out.println(number.nextInt(21));
     }
   } catch (NoSuchAlgorithmException nsae) { 
     // Forward to handler
   }
}

Exceptions

MSC02-J-EX0: Using the default constructor for java.util.Random applies a seed value that is "very likely to be distinct from any other invocation of this constructor" [API 2014] and may improve security marginally. As a result, it may be used only for noncritical applications operating on nonsensitive data. Java's default seed uses the system's time in milliseconds. When used, explicit documentation of this exception is required.

...

For noncritical cases, such as adding some randomness to a game or unit testing, the use of class Random is acceptable. However, it is worth reiterating that the resulting low-entropy random numbers are insufficiently random to be used for more security-critical applications, such as cryptography.

MSC02-J-EX1: Predictable sequences of pseudorandom numbers are required in some cases, such as when running regression tests of program behavior. Use of the insecure java.util.Random class is permitted in such cases. However, security-related applications may invoke this exception only for testing purposes; this exception may not be applied in a production context.

...