How does the Mersenne's Twister work? posted February 2016

Someone asked that question on reddit, and so I replied with a high level answer that should provide a clear enough view of the algorithm:

From a high level, here's what a PRNG is supposed to look like:

you start with a seed (if you re-use the same seed you will obtain the same random numbers), you initialize it into a state. Then, every time you want to obtain a random number, you transform that state with a one-way function gg. This is because you don't want people to find out the state out of the random output.

You want another random number? You first transform the state with a one way function ff: this is because you don't want people who found out the state to be able to retrieve past states (forward secrecy). And then you use your function gg again to output a random number.

Mersenne Twister (MT) is like that, except:

• your first state is not used to output any random numbers
• a state allows you to output not only one, but 624 random numbers (although this could be thought as one big random number)
• the gg function is reversible, it's not a one-way function, so MT it is not a cryptographically secure PRNG.

With more details, here's what MT looks like:

the ff function is called "twist", the gg function is called "temper". You can find out how each functions work by looking at the working code on the wikipedia page of MT.