I've read the Chapter "Randomness" from the Serious Cryptography book and it raised some questions. Namely:
It is written that Mersenne Twister is proved to be cryptographically irreliable. And that is it used by some languages, especially by Python. I have seen a lot of project with different languages when secure random stuff (like keys, token, sessions and so on) were generated just by taking random bits from a standard library.
I have not seen a situation when someone takes care of entropy level.
How to know that generating (pseudo) random keys is secure? Especially, I don't see implementation of pseudorandom generator that return error (for example when entropy is not sufficient). Could tell me something about my doubts and recommend me any book/article that covers that subject more specifically.