Android Question Backward Seed?

[Quillok]

Hey,
actually I'm thinking about if it is possible to use random and seed to generate a large number.

Let me explain:
I've got the number 123456789
Now I want to get the exact number on another device using the seed possibility.
Would it be possible to "create" a seed that would definitely throw this number when using rnd(0,999999999)?

 

[emexes]

The pseudorandom sequence is something like:

new_state = (old_state * C1 + C2) modulo N

where C1 and N are probably prime, or at least prime relative to each other, so that the sequence would travel through every possibility before repeating. Presumably nowadays the randomizing function is more complicated.

I also remember a story about people cracking an online poker site because they worked out the random number generator sequence and thus had a good idea of which cards the other players were likely to have. The headline had me thinking it was a made-up story, but when digging into it a bit deeper, it actually seemed plausible.

Anyway, I am off to dump a few random numbers, see how we go. 16-bit sequences would be no problem, 32-bit would be doable with effort, 64-bit would be... interesting.

 

[emexes]

Try:

RndSeed(12288128)
Log(Rnd(0, 999999999))

RndSeed(101501290)
Log(Rnd(0, 999999999))

RndSeed(592276329)
Log(Rnd(0, 999999999))

I am mildly worried that there are three 9-digit seeds that produce the same 9-digit random number - this makes me think that there exist some 9-digit random numbers that don't have a 9-digit seed. Hmm. Although probably there is a 10 or 11 digit seed that will do the job.

Anyway, the other minor issue is that the documentation for Rnd() says:

ie Rnd(0, 999999999) will never return 999999999 (per "Max (exclusive)") and thus it would be better to use Rnd(0, 1000000000) eg:

RndSeed(12288128)
Log(Rnd(0, 1000000000))

RndSeed(592276329)
Log(Rnd(0, 1000000000))

 

[emexes]

The most relevant article to your quest that I found is:

https://franklinta.com/2014/08/31/predicting-the-next-math-random-in-java/

which looks plausible but made me very sleepy. This article, on the other hand, is rivetting:

https://www.datamation.com/entdev/a...Online-Poker-A-Study-in-Software-Security.htm

Seems to be missing some diagrams, but let's just call that free exercise for the imagination!