Securerandom things ｜ true and false random numbers

The previous articles , This paper introduces several ways of generating random numbers , So what is pseudo-random number ？

So called pseudo-random numbers , It means as long as given ⼀ Initial species ⼦, production ⽣ The random number sequence of is complete ⼀ What kind of .

for (int i = 0; i < 10; i++) {
    
    Random random = new Random(123);
    int randomValue = random.nextInt(10);
    System.out.println(randomValue);
}

When we initialize Random When no seed is given , The current time will be given as the seed by default .

    /** * Creates a new random number generator. This constructor sets * the seed of the random number generator to a value very likely * to be distinct from any other invocation of this constructor. */
    public Random() {
    
        this(seedUniquifier() ^ System.nanoTime());
    }

track

     * @return the current value of the running Java Virtual Machine's
     *         high-resolution time source, in nanoseconds
     * @since 1.5
     */
    public static native long nanoTime();

that , What is a true random number ？

Real random numbers can only pass through quantities ⼦⼒ Learn principles to get ,⽽ What we want is ⼀ An unpredictable, secure random
Count ,SecureRandom Namely ⽤ To create safe random numbers ：

SecureRandom sr = new SecureRandom();
System.out.println(sr.nextInt(100));

SecureRandom⽆ Cannot designate species ⼦, It makes ⽤RNG（random number generator） Algorithm .JDK Of SecureRandom There are actually many different underlying implementations , Some envoys ⽤ Safe random species ⼦ Add the pseudo-random number algorithm to produce ⽣ Safe random number , Some envoys ⽤ Real random number ⽣ Make it .

Actually make ⽤ When , Priority can be given to ⾼ Safe random number of intensity ⽣ Make it , If not provided , Then make ⽤ Ordinary level of safety random number ⽣ Make it ：

import java.util.Arrays;
import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;
public class Main {
    
    public static void main(String[] args) {
    
        SecureRandom sr = null;
        try {
    
       		//  obtain ⾼ Strength safety random number ⽣ Make it 
            sr = SecureRandom.getInstanceStrong(); 
        } catch (NoSuchAlgorithmException e) {
    
            //  Get ordinary safe random numbers ⽣ Make it 
            sr = new SecureRandom(); 
        }
}

SecureRandom The security of is a random kind of security provided by the operating system ⼦ Come on ⽣ Into random numbers .

This species ⼦ It's through CPU The hot noise of 、 Read and write the bytes of the disk 、⽹ Network flow and other random events produce ⽣ Of “ entropy ”.

In cryptography , Safe random number ⾮ Always important . If so ⽤ Unsafe pseudo-random numbers , All encryption systems will be broken .

therefore , Always remember that you must make ⽤SecureRandom To produce ⽣ Safe random number .