Predicting the outcome of PHP rand() function given a seeded value

Asked Mar 20 '17 at 20:13

Active Mar 21 '17 at 12:48

Viewed 188 times

Recently I've been getting into the whole idea of LCGs and Pseudorandom number generators. Anyway, I though that PHP should be a good starting point.

My question is, given a seeded number (done through srand() ) how does one predict the next number in the rand() sequence?

From what I understand the function should be something like (SEED * A + C) mod M How can I find the values of A, C, and M? And if I find those values, can I predict the next number in the sequence?

EDIT: Prior to version 7.0 where rand() becomes an alias of mt_rand()

edited Mar 21 '17 at 12:48

asked Mar 20 '17 at 20:13

Redseb

*"How can I find the values of A, C, and M"* -- you can find them in the [source code of PHP](https://github.com/php/php-src). – axiac Mar 20 '17 at 20:27
1

https://github.com/php/php-src/blob/master/ext/standard/php_rand.h – AbraCadaver Mar 20 '17 at 20:29

Predicting the outcome of PHP rand() function given a seeded value

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