CODEWITHSUNDEEP
javascript
user6938336
user6938336

Reputation:

How can I predict Math.random results?

How can I predict the results from a roulette gaming website csgopolygon.com, given that it is calling Math.random and Math.floor?

Upvotes: 19

Views: 10320

Answers (2)

David
David

Reputation: 47

You can't, and you probably shouldn't develop a gambling addiction as a 16-year-old. That said, even if you could, that site isn't using JavaScript to generate a number, but a server-side language like PHP or ASP.NET.

Upvotes: -1

Stijn de Witt
Stijn de Witt

Reputation: 42104

Your hunch that it is, in theory, possible to predict the results of Math.random is correct. This is why, if you ever want to build a gaming/gambling application, you should make sure to use a cryptographically secure pseudo-random number generator. If they are using such, then forget about it.

If however you are correct and they are using System.time as the seed to the standard Random generator that comes with Java, there might be a way. It would involve generating millions of numbers sequences with millions of numbers in each sequence, based on seeds corresponding to (future) timestamps, then observing the actual random numbers generated by the website and trying to find the specific sequence among the millions you generated beforehand. If you have a match, you found the seed. And if you have the seed and know where in the sequence they are, you could then theoretically predict the next numbers.

Problems with this approach:

  1. You need to know the exact algorithm they are using, so you can make sure you are using the same
  2. It would take huge amounts of processing power to generate all the sequences
  3. It would take huge amounts of storage to store them
  4. It would take huge amounts of processing power to search the observed sequence among the stored sequences
  5. You don't have the full picture. Even if you found the right seed and position in that seed's sequence, you still need to predict the next number that you will get, but as it's a multiplayer site (I assume), they might be giving that number to another player.

In other answers it is said that predicting the results of Math.random is impossible. This is incorrect. Math.random is actually very predictable, once you know the seed and the iteration (how many numbers were generated since the seed was set). I actually once built a game that generated random levels. I was messing with the seed and found that if I always set the same seed, I would always get the same levels. Which was cool because my game had infinite levels, but level 27 (for example) always looked exactly the same.

However,

  1. They are not using Java. Check out the 'Provably Fair' link at the top. They discuss how you can verify past rolls yourself by executing PHP code.
  2. These guys are smart. They are publishing the old seeds once they dismiss it. This allows you (using the predictable behavior of pseudo-random number generators) to re-generate all rolls and verify that they never tampered with them.

Basically, you want to find the seed that is currently in use... However, point 5 I mentioned above still holds: you don't have the full picture, so how would you predict what roll you would be getting? Apart from that, finding the seed will prove near impossible. These guys know cryptography, so you can bet they are using a secure random number generator.

Upvotes: 20

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