PHP mt_rand() function

Question

Are PHP random numbers predictable? if so, how difficult would it be to predict random numbers that are in a range of 1 to 32? and is there any way to make it unpredictable?

<?php
function rand_best($min, $max) {
    $generated = array();
    for ($i = 0; $i < 100; $i++) {
        $generated[] = mt_rand($min, $max);
    }
    shuffle($generated);
    $position = mt_rand(0, 99);
    return $generated[$position];
}
?>

Since you are using mt_rand(), you should read up on the Mersenne Twister algorithm if you want to know how it works. — DaveRandom
– DaveRandom, Commented Jan 5, 2012 at 11:49
Additionally, mt_rand() provides better quality than rand() (which is notably flawed). BTW, not random, not uniform and predictable are pretty different concepts: you just can't predict the next number if you don't know the seed. — Álvaro González
– Álvaro González, Commented Jan 5, 2012 at 11:53

OptimusCrime · Accepted Answer · 2012-01-05 11:50:11Z

7

The discussion around how random random-functions in programming is, is ancient.

Take a look at this: http://en.wikipedia.org/wiki/Random_number_generation

Anyway. The random-functions are so good today that they are (what I would call) as near random as possible. There's no way to predict a result between 1,32 (or any other number for that sake). The deal is that the numbers are not truly random because a computer can not do such a operation.

I'd say the rand-functions is more than good enough unless you are writing something for Pentagon

answered Jan 5, 2012 at 11:50

OptimusCrime

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4 Comments

Basile Starynkevitch Over a year ago

Some computers have hardware devices producing really random numbers.

OptimusCrime Over a year ago

That's true. I've read on this page random.org/randomness (should be read!) that they use a radioactive source, because they are truly random.

Basile Starynkevitch Over a year ago

I think the some very latest Intel processors have a random generating privileged instruction.

tne Over a year ago

"Writing for the Pentagon" or even more intense: making an HTTPS request. Seriously, good randomness sources are needed everywhere or things as we know them wouldn't function at all. I don't think it's right to shove the concept under the rug because it might not be immediately intuitive. You don't need radioactive sources for those basic cases either, and all modern kernels are able to gather good-enough randomness from common sources to feed a pool used for seeding PRNGs. On-topic answer.

Basile Starynkevitch · Accepted Answer · 2012-01-05 11:49:16Z

2

Assuming a Linux system, you could seed your pseudo random number generator with /dev/urandom (or read from that), or possibly /dev/random (be careful, it can block).

answered Jan 5, 2012 at 11:49

Basile Starynkevitch

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Comments

Kenan Duman · Accepted Answer · 2018-05-23 14:32:21Z

1

After PHP 7 version you can use random_int() too.
Take a look at this: http://php.net/random_int

answered May 23, 2018 at 14:32

Kenan Duman

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