Struct pallet_babe::RandomnessFromTwoEpochsAgo[−][src]

pub struct RandomnessFromTwoEpochsAgo<T>(_);

Expand description

Randomness usable by consensus protocols that depend upon finality and take action based upon on-chain commitments made during the epoch before the previous epoch.

An off-chain consensus protocol requires randomness be finalized before usage, but one extra epoch delay beyond RandomnessFromOneEpochAgo suffices, under the assumption that finality never stalls for longer than one 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 RandomnessFromTwoEpochsAgo should come from at least three epochs ago. We require BABE session keys be registered at least three epochs before being used to derive CurrentBlockRandomness for example.

All users learn RandomnessFromTwoEpochsAgo when epoch current_epoch - 1 starts, although some learn it a few block earlier inside epoch current_epoch - 2.

Adversaries with enough block producers could bias this randomness by choosing upon what their block producers build at the end of epoch current_epoch - 2 or the beginning epoch current_epoch - 1, or skipping slots at the end of epoch current_epoch - 2.

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.

Trait Implementations

impl<T: Config> Randomness<<T as Config>::Hash, <T as Config>::BlockNumber> for RandomnessFromTwoEpochsAgo<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. Read more

fn random_seed() -> (Output, BlockNumber)

Get the basic random seed. Read more

Auto Trait Implementations

impl<T> RefUnwindSafe for RandomnessFromTwoEpochsAgo<T> where
    T: RefUnwindSafe,

impl<T> Send for RandomnessFromTwoEpochsAgo<T> where
    T: Send,

impl<T> Sync for RandomnessFromTwoEpochsAgo<T> where
    T: Sync,

impl<T> Unpin for RandomnessFromTwoEpochsAgo<T> where
    T: Unpin,

impl<T> UnwindSafe for RandomnessFromTwoEpochsAgo<T> where
    T: UnwindSafe,

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized,

pub fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more

impl<T> Borrow<T> for T where
    T: ?Sized,

pub fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

impl<T> BorrowMut<T> for T where
    T: ?Sized,

pub fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

impl<T> CheckedConversion for T

fn checked_from<T>(t: T) -> Option<Self> where
    Self: TryFrom<T>,

Convert from a value of T into an equivalent instance of Option<Self>. Read more

fn checked_into<T>(self) -> Option<T> where
    Self: TryInto<T>,

Consume self to return Some equivalent value of Option<T>. Read more

impl<T> Downcast for T where
    T: Any,

pub fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait. Read more

pub fn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait. Read more

pub fn as_any(&self) -> &(dyn Any + 'static)

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s. Read more

pub fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s. Read more

impl<T> DowncastSync for T where
    T: Any + Send + Sync,

pub fn into_any_arc(self: Arc<T>) -> Arc<dyn Any + Sync + Send + 'static>

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<ConcreteType> where ConcreteType implements Trait. Read more

impl<T> From<T> for T

pub fn from(t: T) -> T

Performs the conversion.

impl<T> Instrument for T

fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more

fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more

impl<T, U> Into<U> for T where
    U: From<T>,

pub fn into(self) -> U

Performs the conversion.

impl<T> IsType<T> for T

pub fn from_ref(t: &T) -> &T

Cast reference.

pub fn into_ref(&self) -> &T

Cast reference.

pub fn from_mut(t: &mut T) -> &mut T

Cast mutable reference.

pub fn into_mut(&mut self) -> &mut T

Cast mutable reference.

impl<T, Outer> IsWrappedBy<Outer> for T where
    T: From<Outer>,
    Outer: AsRef<T> + AsMut<T> + From<T>,

pub fn from_ref(outer: &Outer) -> &T

Get a reference to the inner from the outer.

pub fn from_mut(outer: &mut Outer) -> &mut T

Get a mutable reference to the inner from the outer.

impl<T> Same<T> for T

type Output = T

Should always be Self

impl<T> SaturatedConversion for T

fn saturated_from<T>(t: T) -> Self where
    Self: UniqueSaturatedFrom<T>,

Convert from a value of T into an equivalent instance of Self. Read more

fn saturated_into<T>(self) -> T where
    Self: UniqueSaturatedInto<T>,

Consume self to return an equivalent value of T. Read more

impl<SS, SP> SupersetOf<SS> for SP where
    SS: SubsetOf<SP>,

pub fn to_subset(&self) -> Option<SS>

The inverse inclusion map: attempts to construct self from the equivalent element of its superset. Read more

pub fn is_in_subset(&self) -> bool

Checks if self is actually part of its subset T (and can be converted to it).

pub fn to_subset_unchecked(&self) -> SS

Use with care! Same as self.to_subset but without any property checks. Always succeeds.

pub fn from_subset(element: &SS) -> SP

The inclusion map: converts self to the equivalent element of its superset.

impl<T, U> TryFrom<U> for T where
    U: Into<T>,

type Error = Infallible

The type returned in the event of a conversion error.

pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>,

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.

impl<S, T> UncheckedInto<T> for S where
    T: UncheckedFrom<S>,

pub fn unchecked_into(self) -> T

The counterpart to unchecked_from.

impl<T, S> UniqueSaturatedInto<T> for S where
    T: Bounded,
    S: TryInto<T>,

pub fn unique_saturated_into(self) -> T

Consume self to return an equivalent value of T.

impl<V, T> VZip<V> for T where
    V: MultiLane<T>,

pub fn vzip(self) -> V

impl<T> MaybeRefUnwindSafe for T where
    T: RefUnwindSafe,