[stable2412] Backport #8427 (#8449)

Backport #8427 into `stable2412` from serban300.

See the
[documentation](https://github.com/paritytech/polkadot-sdk/blob/master/docs/BACKPORT.md)
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Co-authored-by: Serban Iorga <serban@parity.io>
Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Adrian Catangiu <adrian@parity.io>

Author: 4 people

prdoc/pr_8427.prdoc

@@ -0,0 +1,9 @@
+title: 'BEEFY: adjust equivocation slash fraction'
+doc:
+- audience: Runtime Dev
+  description: |-
+    Use 50% slash fraction for fork voting and future block voting (in accordance with the https://eprint.iacr.org/2025/057.pdf paper).
+    In order to account for the possible risk of accidental/non-malicious double voting, keep the current formula for double voting proof.
+crates:
+- name: pallet-beefy
+  bump: patch

substrate/frame/beefy/src/equivocation.rs

@@ -81,6 +81,8 @@ where
 	pub validator_set_count: u32,
 	/// The authority which produced this equivocation.
 	pub offender: Offender,
+	/// Optional slash fraction
+	maybe_slash_fraction: Option<Perbill>,
 }
 
 impl<Offender: Clone, N> Offence<Offender> for EquivocationOffence<Offender, N>
@@ -106,10 +108,14 @@ where
 		self.time_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
+		if let Some(slash_fraction) = self.maybe_slash_fraction {
+			return slash_fraction;
+		}
+
+		// `Perbill` type domain is [0, 1] by definition
+		// The formula is min((3k / n)^2, 1)
+		// where k = offenders_number and n = validators_number
 		Perbill::from_rational(3 * offenders_count, self.validator_set_count).square()
 	}
 }
@@ -257,6 +263,14 @@ impl<T: Config> EquivocationEvidenceFor<T> {
 			},
 		}
 	}
+
+	fn slash_fraction(&self) -> Option<Perbill> {
+		match self {
+			EquivocationEvidenceFor::DoubleVotingProof(_, _) => None,
+			EquivocationEvidenceFor::ForkVotingProof(_, _) |
+			EquivocationEvidenceFor::FutureBlockVotingProof(_, _) => Some(Perbill::from_percent(50)),
+		}
+	}
 }
 
 impl<T, R, P, L> OffenceReportSystem<Option<T::AccountId>, EquivocationEvidenceFor<T>>
@@ -305,6 +319,7 @@ where
 		reporter: Option<T::AccountId>,
 		evidence: EquivocationEvidenceFor<T>,
 	) -> Result<(), DispatchError> {
+		let maybe_slash_fraction = evidence.slash_fraction();
 		let reporter = reporter.or_else(|| pallet_authorship::Pallet::<T>::author());
 
 		// We check the equivocation within the context of its set id (and associated session).
@@ -333,6 +348,7 @@ where
 			session_index,
 			validator_set_count: validator_count,
 			offender,
+			maybe_slash_fraction,
 		};
 		R::report_offence(reporter.into_iter().collect(), offence)
 			.map_err(|_| Error::<T>::DuplicateOffenceReport.into())

substrate/frame/beefy/src/tests.rs

@@ -16,7 +16,10 @@
 // limitations under the License.
 
 use codec::Encode;
-use std::vec;
+use std::{
+	ops::{Mul, Sub},
+	vec,
+};
 
 use frame_support::{
 	assert_err, assert_ok,
@@ -32,7 +35,7 @@ use sp_consensus_beefy::{
 	},
 	Payload, ValidatorSet, ValidatorSetId, KEY_TYPE as BEEFY_KEY_TYPE,
 };
-use sp_runtime::DigestItem;
+use sp_runtime::{DigestItem, Perbill};
 use sp_session::MembershipProof;
 
 use crate::{self as beefy, mock::*, Call, Config, Error, WeightInfoExt};
@@ -309,8 +312,13 @@ fn report_double_voting(
 	)
 }
 
-fn report_equivocation_current_set_works(mut f: impl ReportEquivocationFn) {
+fn report_equivocation_current_set_works(
+	mut f: impl ReportEquivocationFn,
+	hardcoded_slash_fraction: Option<Perbill>,
+) {
 	let authorities = test_authorities();
+	let initial_balance = 10_000_000;
+	let initial_slashable_balance = 10_000;
 
 	ExtBuilder::default().add_authorities(authorities).build_and_execute(|| {
 		assert_eq!(Staking::current_era(), Some(0));
@@ -326,12 +334,16 @@ fn report_equivocation_current_set_works(mut f: impl ReportEquivocationFn) {
 
 		// make sure that all validators have the same balance
 		for validator in &validators {
-			assert_eq!(Balances::total_balance(validator), 10_000_000);
-			assert_eq!(Staking::slashable_balance_of(validator), 10_000);
+			assert_eq!(Balances::total_balance(validator), initial_balance);
+			assert_eq!(Staking::slashable_balance_of(validator), initial_slashable_balance);
 
 			assert_eq!(
 				Staking::eras_stakers(1, &validator),
-				pallet_staking::Exposure { total: 10_000, own: 10_000, others: vec![] },
+				pallet_staking::Exposure {
+					total: initial_slashable_balance,
+					own: initial_slashable_balance,
+					others: vec![]
+				},
 			);
 		}
 
@@ -351,8 +363,22 @@ fn report_equivocation_current_set_works(mut f: impl ReportEquivocationFn) {
 		// check that the balance of 0-th validator is slashed 100%.
 		let equivocation_validator_id = validators[equivocation_authority_index];
 
-		assert_eq!(Balances::total_balance(&equivocation_validator_id), 10_000_000 - 10_000);
-		assert_eq!(Staking::slashable_balance_of(&equivocation_validator_id), 0);
+		if let Some(slash_fraction) = hardcoded_slash_fraction {
+			assert_eq!(
+				Balances::total_balance(&equivocation_validator_id),
+				initial_balance - slash_fraction.mul(initial_slashable_balance)
+			);
+			assert_eq!(
+				Staking::slashable_balance_of(&equivocation_validator_id),
+				Perbill::from_percent(100).sub(slash_fraction).mul(initial_slashable_balance)
+			);
+		} else {
+			assert_eq!(
+				Balances::total_balance(&equivocation_validator_id),
+				initial_balance - initial_slashable_balance
+			);
+			assert_eq!(Staking::slashable_balance_of(&equivocation_validator_id), 0);
+		}
 		assert_eq!(
 			Staking::eras_stakers(2, &equivocation_validator_id),
 			pallet_staking::Exposure { total: 0, own: 0, others: vec![] },
@@ -364,19 +390,28 @@ fn report_equivocation_current_set_works(mut f: impl ReportEquivocationFn) {
 				continue
 			}
 
-			assert_eq!(Balances::total_balance(validator), 10_000_000);
-			assert_eq!(Staking::slashable_balance_of(validator), 10_000);
+			assert_eq!(Balances::total_balance(validator), initial_balance);
+			assert_eq!(Staking::slashable_balance_of(validator), initial_slashable_balance);
 
 			assert_eq!(
 				Staking::eras_stakers(2, &validator),
-				pallet_staking::Exposure { total: 10_000, own: 10_000, others: vec![] },
+				pallet_staking::Exposure {
+					total: initial_slashable_balance,
+					own: initial_slashable_balance,
+					others: vec![]
+				},
 			);
 		}
 	});
 }
 
-fn report_equivocation_old_set_works(mut f: impl ReportEquivocationFn) {
+fn report_equivocation_old_set_works(
+	mut f: impl ReportEquivocationFn,
+	hardcoded_slash_fraction: Option<Perbill>,
+) {
 	let authorities = test_authorities();
+	let initial_balance = 10_000_000;
+	let initial_slashable_balance = 10_000;
 
 	ExtBuilder::default().add_authorities(authorities).build_and_execute(|| {
 		start_era(1);
@@ -398,12 +433,16 @@ fn report_equivocation_old_set_works(mut f: impl ReportEquivocationFn) {
 
 		// make sure that all authorities have the same balance
 		for validator in &validators {
-			assert_eq!(Balances::total_balance(validator), 10_000_000);
-			assert_eq!(Staking::slashable_balance_of(validator), 10_000);
+			assert_eq!(Balances::total_balance(validator), initial_balance);
+			assert_eq!(Staking::slashable_balance_of(validator), initial_slashable_balance);
 
 			assert_eq!(
 				Staking::eras_stakers(2, &validator),
-				pallet_staking::Exposure { total: 10_000, own: 10_000, others: vec![] },
+				pallet_staking::Exposure {
+					total: initial_slashable_balance,
+					own: initial_slashable_balance,
+					others: vec![]
+				},
 			);
 		}
 
@@ -421,8 +460,22 @@ fn report_equivocation_old_set_works(mut f: impl ReportEquivocationFn) {
 		// check that the balance of 0-th validator is slashed 100%.
 		let equivocation_validator_id = validators[equivocation_authority_index];
 
-		assert_eq!(Balances::total_balance(&equivocation_validator_id), 10_000_000 - 10_000);
-		assert_eq!(Staking::slashable_balance_of(&equivocation_validator_id), 0);
+		if let Some(slash_fraction) = hardcoded_slash_fraction {
+			assert_eq!(
+				Balances::total_balance(&equivocation_validator_id),
+				initial_balance - slash_fraction.mul(initial_slashable_balance)
+			);
+			assert_eq!(
+				Staking::slashable_balance_of(&equivocation_validator_id),
+				Perbill::from_percent(100).sub(slash_fraction).mul(initial_slashable_balance)
+			);
+		} else {
+			assert_eq!(
+				Balances::total_balance(&equivocation_validator_id),
+				initial_balance - initial_slashable_balance
+			);
+			assert_eq!(Staking::slashable_balance_of(&equivocation_validator_id), 0);
+		}
 		assert_eq!(
 			Staking::eras_stakers(3, &equivocation_validator_id),
 			pallet_staking::Exposure { total: 0, own: 0, others: vec![] },
@@ -434,12 +487,16 @@ fn report_equivocation_old_set_works(mut f: impl ReportEquivocationFn) {
 				continue
 			}
 
-			assert_eq!(Balances::total_balance(validator), 10_000_000);
-			assert_eq!(Staking::slashable_balance_of(validator), 10_000);
+			assert_eq!(Balances::total_balance(validator), initial_balance);
+			assert_eq!(Staking::slashable_balance_of(validator), initial_slashable_balance);
 
 			assert_eq!(
 				Staking::eras_stakers(3, &validator),
-				pallet_staking::Exposure { total: 10_000, own: 10_000, others: vec![] },
+				pallet_staking::Exposure {
+					total: initial_slashable_balance,
+					own: initial_slashable_balance,
+					others: vec![]
+				},
 			);
 		}
 	});
@@ -579,12 +636,12 @@ fn valid_equivocation_reports_dont_pay_fees(mut f: impl ReportEquivocationFn) {
 
 #[test]
 fn report_double_voting_current_set_works() {
-	report_equivocation_current_set_works(report_double_voting);
+	report_equivocation_current_set_works(report_double_voting, None);
 }
 
 #[test]
 fn report_double_voting_old_set_works() {
-	report_equivocation_old_set_works(report_double_voting);
+	report_equivocation_old_set_works(report_double_voting, None);
 }
 
 #[test]
@@ -812,12 +869,12 @@ fn report_fork_voting(
 
 #[test]
 fn report_fork_voting_current_set_works() {
-	report_equivocation_current_set_works(report_fork_voting);
+	report_equivocation_current_set_works(report_fork_voting, Some(Perbill::from_percent(50)));
 }
 
 #[test]
 fn report_fork_voting_old_set_works() {
-	report_equivocation_old_set_works(report_fork_voting);
+	report_equivocation_old_set_works(report_fork_voting, Some(Perbill::from_percent(50)));
 }
 
 #[test]
@@ -1007,12 +1064,15 @@ fn report_future_block_voting(
 
 #[test]
 fn report_future_block_voting_current_set_works() {
-	report_equivocation_current_set_works(report_future_block_voting);
+	report_equivocation_current_set_works(
+		report_future_block_voting,
+		Some(Perbill::from_percent(50)),
+	);
 }
 
 #[test]
 fn report_future_block_voting_old_set_works() {
-	report_equivocation_old_set_works(report_future_block_voting);
+	report_equivocation_old_set_works(report_future_block_voting, Some(Perbill::from_percent(50)));
 }
 
 #[test]