What are the best up-to-date secure approaches of generating pseudorandom number in Solidity? [duplicate]

Question

I am thinking about creating a lottery with more than one winner and one round for users. Please don't consider usual 'commit-reveal' scheme. However, person can claim rewards on their own at the end of the lottery.

So, generation of pseudorandom number is essential.
I'm looking forward for approaches without 3d party involvement.
I would be very grateful to all answers!

Answer 1

In short:

There's no "safe" way to generate pseudo-random numbers in smart contracts if those numbers are used for critical functions. The only plausible solution (for now) is an Oracle.

In your case, creating a pseudo-random number in a smart contract for something like a lottery is a bit like trying to keep a secret everyone can figure out. Since everything on the blockchain is transparent, anyone with enough know-how can predict the number. So you need to account for that.

If you can implement the lottery system such that knowing the results of the pseudo-random-number generating function offers no advantage, you are good. But I don't see a legit way fo accomplish that.

Answer 2

This question already has been asked and answered more than once.

If you are building a lottery, pseudorandom is not safe, for lotteries or gambling since it can be found or manipulated.

However, on top of all the other solution easy to find with a simple search, there is now a new solution to pseudo-randomness and answering this now could prevent future duplicates:

• Since the Ethereum merge the new opcode prevrandao made its appearance, to replace the previous difficulty:

Useful links:

• The official EIP

• use of prevrandao()

• other stackoverflow possible uses and opinions