Provably Fair

Raffle uses NoisRNG - https://nois.network/ as a source of randomness during the raffle draw. The raffle can only be drawn by us randomly after the end. This ensures that no one can draw the raffle during a favorable time.

The randomness is then used to determine the winner by generating a random number with the code below:

pub fn extractWinner(raffle: Raffle){
    let randomness: [u8; 32] = randomness
                               .to_array()
                               .maperr(|| ContractError::InvalidRandomness)?;
    let winner_index = int_in_range(randomness, 0, (raffle.ticket_list.len() - 1) as u64);
    let winner = if winner_index < raffle.ticket_list.len() as u64 {
                        raffle.ticket_list[winner_index as usize].clone()
                    }
                 else {
                        raffle.creator.clone()
        };
}

let winner = extractWinner(raffle);

Here winner_index is the index of winner drawn i.e. 0 for 1st winner, 1 for 2nd winner and so on. The random number is then used to find the winner's index from the list of buyers stored onchain.