Struct pallet_babe::RandomnessFromOneEpochAgo

pub struct RandomnessFromOneEpochAgo<T>(_);

Randomness usable by on-chain code that does not depend upon finality and takes action based upon on-chain commitments made during the previous epoch.

All randomness is relative to commitments to any other inputs to the computation: If Alice samples randomness near perfectly using radioactive decay, but then afterwards Eve selects an arbitrary value with which to xor Alice’s randomness, then Eve always wins whatever game they play.

All input commitments used with RandomnessFromOneEpochAgo should come from at least two epochs ago, although the previous epoch might work in special cases under additional assumption.

All users learn RandomnessFromOneEpochAgo at the end of the previous epoch, although some block producers learn it several block earlier.

Adversaries with enough block producers could bias this randomness by choosing upon what their block producers build at either the end of the previous epoch or the beginning of the current epoch, or electing to skipping some of their own block production slots towards the end of the previous epoch.

Adversaries should not possess many block production slots towards the beginning or end of every epoch, but they possess some influence over when they possess more slots.

As an example usage, we determine parachain auctions ending times in Polkadot using RandomnessFromOneEpochAgo because it reduces bias from ParentBlockRandomness and does not require the extra finality delay of RandomnessFromTwoEpochsAgo.

Trait Implementations

impl<T: Config> Randomness<<T as Config>::Hash, <T as Config>::BlockNumber> for RandomnessFromOneEpochAgo<T>

fn random(subject: &[u8]) -> (T::Hash, T::BlockNumber)

Get the most recently determined random seed, along with the time in the past since when it was determinable by chain observers.

fn random_seed() -> (Output, BlockNumber)

Get the basic random seed.