Better Random Generating PHP

Question

I know that just using rand() is predictable, if you know what you're doing, and have access to the server.

I have a project that is highly dependent upon choosing a random number that is as unpredictable as possible. So I'm looking for suggestions, either other built-in functions or user functions, that can generate a better random number.

I used this to do a little test:

$i = 0;  while($i < 10000){     $rand = rand(0, 100);      if(!isset($array[$rand])){         $array[$rand] = 1;     } else {         $array[$rand]++;     }      sort($array);     $i++; } 

I found the results to be evenly distributed, and there is an odd pattern to the number of times each number is generated.

Answer 1

Adding, multiplying, or truncating a poor random source will give you a poor random result. See Introduction to Randomness and Random Numbers for an explanation.

You're right about PHP rand() function. See the second figure on Statistical Analysis for a striking illustration. (The first figure is striking, but it's been drawn by Scott Adams, not plotted with rand()).

One solution is to use a true random generator such as random.org. Another, if you're on Linux/BSD/etc. is to use /dev/random. If the randomness is mission critical, you will have to use a hardware random generator.