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// This file is part of Substrate.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! An opt-in utility module for reporting equivocations.
//!
//! This module defines an offence type for BABE equivocations
//! and some utility traits to wire together:
//! - a system for reporting offences;
//! - a system for submitting unsigned transactions;
//! - a way to get the current block author;
//! These can be used in an offchain context in order to submit equivocation
//! reporting extrinsics (from the client that's import BABE blocks).
//! And in a runtime context, so that the BABE pallet can validate the
//! equivocation proofs in the extrinsic and report the offences.
//! IMPORTANT:
//! When using this module for enabling equivocation reporting it is required
//! that the `ValidateUnsigned` for the BABE pallet is used in the runtime
//! definition.
use alloc::{boxed::Box, vec, vec::Vec};
use frame_support::traits::{Get, KeyOwnerProofSystem};
use frame_system::pallet_prelude::HeaderFor;
use log::{error, info};
use sp_consensus_babe::{AuthorityId, EquivocationProof, Slot, KEY_TYPE};
use sp_runtime::{
transaction_validity::{
InvalidTransaction, TransactionPriority, TransactionSource, TransactionValidity,
TransactionValidityError, ValidTransaction,
},
DispatchError, KeyTypeId, Perbill,
};
use sp_session::{GetSessionNumber, GetValidatorCount};
use sp_staking::{
offence::{Kind, Offence, OffenceReportSystem, ReportOffence},
SessionIndex,
use crate::{Call, Config, Error, Pallet, LOG_TARGET};
/// BABE equivocation offence report.
///
/// When a validator released two or more blocks at the same slot.
pub struct EquivocationOffence<Offender> {
/// A babe slot in which this incident happened.
pub slot: Slot,
/// The session index in which the incident happened.
pub session_index: SessionIndex,
/// The size of the validator set at the time of the offence.
pub validator_set_count: u32,
/// The authority that produced the equivocation.
pub offender: Offender,
}
impl<Offender: Clone> Offence<Offender> for EquivocationOffence<Offender> {
const ID: Kind = *b"babe:equivocatio";
type TimeSlot = Slot;
fn offenders(&self) -> Vec<Offender> {
vec![self.offender.clone()]
fn session_index(&self) -> SessionIndex {
self.session_index
fn validator_set_count(&self) -> u32 {
self.validator_set_count
fn time_slot(&self) -> Self::TimeSlot {
self.slot
// The formula is min((3k / n)^2, 1)
// where k = offenders_number and n = validators_number
fn slash_fraction(&self, offenders_count: u32) -> Perbill {
// Perbill type domain is [0, 1] by definition
Perbill::from_rational(3 * offenders_count, self.validator_set_count).square()
/// BABE equivocation offence report system.
/// This type implements `OffenceReportSystem` such that:
/// - Equivocation reports are published on-chain as unsigned extrinsic via
/// `offchain::SendTransactionTypes`.
/// - On-chain validity checks and processing are mostly delegated to the user provided generic
/// types implementing `KeyOwnerProofSystem` and `ReportOffence` traits.
/// - Offence reporter for unsigned transactions is fetched via the the authorship pallet.
pub struct EquivocationReportSystem<T, R, P, L>(core::marker::PhantomData<(T, R, P, L)>);
impl<T, R, P, L>
OffenceReportSystem<Option<T::AccountId>, (EquivocationProof<HeaderFor<T>>, T::KeyOwnerProof)>
for EquivocationReportSystem<T, R, P, L>
where
T: Config + pallet_authorship::Config + frame_system::offchain::SendTransactionTypes<Call<T>>,
R: ReportOffence<
T::AccountId,
P::IdentificationTuple,
EquivocationOffence<P::IdentificationTuple>,
>,
P: KeyOwnerProofSystem<(KeyTypeId, AuthorityId), Proof = T::KeyOwnerProof>,
P::IdentificationTuple: Clone,
L: Get<u64>,
{
type Longevity = L;
fn publish_evidence(
evidence: (EquivocationProof<HeaderFor<T>>, T::KeyOwnerProof),
) -> Result<(), ()> {
use frame_system::offchain::SubmitTransaction;
let (equivocation_proof, key_owner_proof) = evidence;
let call = Call::report_equivocation_unsigned {
equivocation_proof: Box::new(equivocation_proof),
key_owner_proof,
let res = SubmitTransaction::<T, Call<T>>::submit_unsigned_transaction(call.into());
match res {
Ok(_) => info!(target: LOG_TARGET, "Submitted equivocation report"),
Err(e) => error!(target: LOG_TARGET, "Error submitting equivocation report: {:?}", e),
res
fn check_evidence(
) -> Result<(), TransactionValidityError> {
// Check the membership proof to extract the offender's id
let key = (sp_consensus_babe::KEY_TYPE, equivocation_proof.offender.clone());
let offender =
P::check_proof(key, key_owner_proof.clone()).ok_or(InvalidTransaction::BadProof)?;
// Check if the offence has already been reported, and if so then we can discard the report.
if R::is_known_offence(&[offender], &equivocation_proof.slot) {
Err(InvalidTransaction::Stale.into())
} else {
Ok(())
fn process_evidence(
reporter: Option<T::AccountId>,
) -> Result<(), DispatchError> {
let reporter = reporter.or_else(|| <pallet_authorship::Pallet<T>>::author());
let offender = equivocation_proof.offender.clone();
let slot = equivocation_proof.slot;
// Validate the equivocation proof (check votes are different and signatures are valid)
if !sp_consensus_babe::check_equivocation_proof(equivocation_proof) {
return Err(Error::<T>::InvalidEquivocationProof.into())
let validator_set_count = key_owner_proof.validator_count();
let session_index = key_owner_proof.session();
let epoch_index =
*slot.saturating_sub(crate::GenesisSlot::<T>::get()) / T::EpochDuration::get();
// Check that the slot number is consistent with the session index
// in the key ownership proof (i.e. slot is for that epoch)
if Pallet::<T>::session_index_for_epoch(epoch_index) != session_index {
return Err(Error::<T>::InvalidKeyOwnershipProof.into())
// Check the membership proof and extract the offender's id
let offender = P::check_proof((KEY_TYPE, offender), key_owner_proof)
.ok_or(Error::<T>::InvalidKeyOwnershipProof)?;
let offence = EquivocationOffence { slot, validator_set_count, offender, session_index };
R::report_offence(reporter.into_iter().collect(), offence)
.map_err(|_| Error::<T>::DuplicateOffenceReport)?;
/// Methods for the `ValidateUnsigned` implementation:
/// It restricts calls to `report_equivocation_unsigned` to local calls (i.e. extrinsics generated
/// on this node) or that already in a block. This guarantees that only block authors can include
/// unsigned equivocation reports.
impl<T: Config> Pallet<T> {
pub fn validate_unsigned(source: TransactionSource, call: &Call<T>) -> TransactionValidity {
if let Call::report_equivocation_unsigned { equivocation_proof, key_owner_proof } = call {
// discard equivocation report not coming from the local node
match source {
TransactionSource::Local | TransactionSource::InBlock => { /* allowed */ },
_ => {
log::warn!(
target: LOG_TARGET,
"rejecting unsigned report equivocation transaction because it is not local/in-block.",
);
return InvalidTransaction::Call.into()
// Check report validity
let evidence = (*equivocation_proof.clone(), key_owner_proof.clone());
T::EquivocationReportSystem::check_evidence(evidence)?;
let longevity =
<T::EquivocationReportSystem as OffenceReportSystem<_, _>>::Longevity::get();
ValidTransaction::with_tag_prefix("BabeEquivocation")
// We assign the maximum priority for any equivocation report.
.priority(TransactionPriority::max_value())
// Only one equivocation report for the same offender at the same slot.
.and_provides((equivocation_proof.offender.clone(), *equivocation_proof.slot))
.longevity(longevity)
// We don't propagate this. This can never be included on a remote node.
.propagate(false)
.build()
InvalidTransaction::Call.into()
pub fn pre_dispatch(call: &Call<T>) -> Result<(), TransactionValidityError> {
T::EquivocationReportSystem::check_evidence(evidence)
Err(InvalidTransaction::Call.into())