Remove Parent Hash to Session mapping (#928)

* Adds a SigningContext type

* Bump spec versions

* Fixes requested changes

* Bump ParachainHost api_version and guard signing_context call

* Improve error message

* If there is no signing_context api use default value

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

polkadot/Cargo.lock

@@ -3956,6 +3956,7 @@ dependencies = [
  "sp-inherents 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
  "sp-runtime 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
  "sp-serializer 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
+ "sp-staking 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
  "sp-std 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
  "sp-trie 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",
  "sp-version 2.0.0-alpha.5 (git+https://github.com/paritytech/substrate)",

polkadot/network/src/legacy/gossip/attestation.rs

@@ -131,9 +131,13 @@ impl View {
 	///
 	/// This will be pruned later on a call to `prune_old_leaves`, when this leaf
 	/// is not a leaf anymore.
-	pub(super) fn new_local_leaf(&mut self, relay_chain_leaf: Hash, validation_data: MessageValidationData) {
+	pub(super) fn new_local_leaf(
+		&mut self,
+		validation_data: MessageValidationData,
+	) {
+		let relay_chain_leaf = validation_data.signing_context.parent_hash.clone();
 		self.leaf_work.push((
-			relay_chain_leaf,
+			validation_data.signing_context.parent_hash.clone(),
 			LeafView {
 				validation_data,
 				knowledge: Default::default(),
@@ -207,7 +211,6 @@ impl View {
 
 				// validate signature.
 				let res = view.validation_data.check_statement(
-					&message.relay_chain_leaf,
 					&message.signed_statement,
 				);
 

polkadot/network/src/legacy/gossip/mod.rs

@@ -60,7 +60,7 @@ use sc_network_gossip::{
 use polkadot_validation::{SignedStatement};
 use polkadot_primitives::{Block, Hash};
 use polkadot_primitives::parachain::{
-	ParachainHost, ValidatorId, ErasureChunk as PrimitiveChunk
+	ParachainHost, ValidatorId, ErasureChunk as PrimitiveChunk, SigningContext,
 };
 use polkadot_erasure_coding::{self as erasure};
 use codec::{Decode, Encode};
@@ -377,13 +377,12 @@ impl RegisteredMessageValidator {
 	/// relevant to this leaf.
 	pub(crate) fn new_local_leaf(
 		&self,
-		relay_chain_leaf: Hash,
 		validation: MessageValidationData,
 	) -> NewLeafActions {
 		// add an entry in attestation_view
 		// prune any entries from attestation_view which are no longer leaves
 		let mut inner = self.inner.inner.write();
-		inner.attestation_view.new_local_leaf(relay_chain_leaf, validation);
+		inner.attestation_view.new_local_leaf(validation);
 
 		let mut actions = Vec::new();
 
@@ -460,11 +459,13 @@ impl GossipService for RegisteredMessageValidator {
 pub(crate) struct MessageValidationData {
 	/// The authorities' parachain validation keys at a block.
 	pub(crate) authorities: Vec<ValidatorId>,
+	/// The signing context.
+	pub(crate) signing_context: SigningContext,
 }
 
 impl MessageValidationData {
 	// check a statement's signature.
-	fn check_statement(&self, relay_chain_leaf: &Hash, statement: &SignedStatement) -> Result<(), ()> {
+	fn check_statement(&self, statement: &SignedStatement) -> Result<(), ()> {
 		let sender = match self.authorities.get(statement.sender as usize) {
 			Some(val) => val,
 			None => return Err(()),
@@ -475,7 +476,7 @@ impl MessageValidationData {
 				&statement.statement,
 				&statement.signature,
 				sender.clone(),
-				relay_chain_leaf,
+				&self.signing_context,
 			);
 
 		if good {
@@ -826,7 +827,9 @@ mod tests {
 		let topic_c = attestation_topic(hash_c);
 
 		// topic_a is in all 3 views -> succeed
-		validator.inner.write().attestation_view.new_local_leaf(hash_a, MessageValidationData::default());
+		let mut validation_data = MessageValidationData::default();
+		validation_data.signing_context.parent_hash = hash_a;
+		validator.inner.write().attestation_view.new_local_leaf(validation_data);
 		// topic_b is in the neighbor's view but not ours -> fail
 		// topic_c is not in either -> fail
 
@@ -937,7 +940,9 @@ mod tests {
 			}
 		});
 		let encoded = statement.encode();
-		validator.inner.write().attestation_view.new_local_leaf(hash_a, MessageValidationData::default());
+		let mut validation_data = MessageValidationData::default();
+		validation_data.signing_context.parent_hash = hash_a;
+		validator.inner.write().attestation_view.new_local_leaf(validation_data);
 
 		{
 			let mut message_allowed = validator.message_allowed();

polkadot/network/src/protocol/mod.rs

@@ -162,7 +162,6 @@ impl NetworkServiceOps for PolkadotNetworkService {
 trait GossipOps: Clone + Send + crate::legacy::GossipService + 'static {
 	fn new_local_leaf(
 		&self,
-		relay_parent: Hash,
 		validation_data: crate::legacy::gossip::MessageValidationData,
 	) -> crate::legacy::gossip::NewLeafActions;
 
@@ -177,10 +176,12 @@ trait GossipOps: Clone + Send + crate::legacy::GossipService + 'static {
 impl GossipOps for RegisteredMessageValidator {
 	fn new_local_leaf(
 		&self,
-		relay_parent: Hash,
 		validation_data: crate::legacy::gossip::MessageValidationData,
 	) -> crate::legacy::gossip::NewLeafActions {
-		RegisteredMessageValidator::new_local_leaf(self, relay_parent, validation_data)
+		RegisteredMessageValidator::new_local_leaf(
+			self,
+			validation_data,
+		)
 	}
 
 	fn register_availability_store(
@@ -804,7 +805,6 @@ impl<Api, Sp, Gossip> Worker<Api, Sp, Gossip> where
 		authorities: Vec<ValidatorId>,
 	) {
 		// glue: let gossip know about our new local leaf.
-		let relay_parent = table.consensus_parent_hash().clone();
 		let (signal, exit) = exit_future::signal();
 
 		let key = table.session_key();
@@ -814,19 +814,20 @@ impl<Api, Sp, Gossip> Worker<Api, Sp, Gossip> where
 			}
 		}
 
+		let signing_context = table.signing_context().clone();
+		let relay_parent = signing_context.parent_hash.clone();
 		let new_leaf_actions = self.gossip_handle.new_local_leaf(
-			relay_parent,
-			crate::legacy::gossip::MessageValidationData { authorities },
+			crate::legacy::gossip::MessageValidationData { authorities, signing_context },
 		);
 
 		new_leaf_actions.perform(&self.gossip_handle);
 
 		self.protocol_handler.consensus_instances.insert(
-			relay_parent,
+			relay_parent.clone(),
 			ConsensusNetworkingInstance {
 				statement_table: table.clone(),
-				relay_parent,
-				attestation_topic: crate::legacy::gossip::attestation_topic(relay_parent),
+				relay_parent: relay_parent.clone(),
+				attestation_topic: crate::legacy::gossip::attestation_topic(relay_parent.clone()),
 				_drop_signal: signal,
 			},
 		);
@@ -1324,7 +1325,7 @@ impl ParachainNetwork for Service {
 	) -> Self::BuildTableRouter {
 		let authorities = authorities.to_vec();
 		let mut sender = self.sender.clone();
-		let relay_parent = table.consensus_parent_hash().clone();
+		let relay_parent = table.signing_context().parent_hash.clone();
 
 		Box::pin(async move {
 			sender.send(

polkadot/network/src/protocol/tests.rs

@@ -20,7 +20,7 @@ use polkadot_primitives::{Block, Header, BlockId};
 use polkadot_primitives::parachain::{
 	Id as ParaId, Chain, DutyRoster, ParachainHost, ValidatorId,
 	Retriable, CollatorId, AbridgedCandidateReceipt,
-	GlobalValidationSchedule, LocalValidationData, ErasureChunk,
+	GlobalValidationSchedule, LocalValidationData, ErasureChunk, SigningContext,
 };
 use polkadot_validation::SharedTable;
 
@@ -114,7 +114,6 @@ impl crate::legacy::GossipService for MockGossip {
 impl GossipOps for MockGossip {
 	fn new_local_leaf(
 		&self,
-		_relay_parent: Hash,
 		_validation_data: crate::legacy::gossip::MessageValidationData,
 	) -> crate::legacy::gossip::NewLeafActions {
 		crate::legacy::gossip::NewLeafActions::new()
@@ -294,6 +293,22 @@ impl ParachainHost<Block> for RuntimeApi {
 	) -> ClientResult<NativeOrEncoded<Option<Vec<AbridgedCandidateReceipt>>>> {
 		Ok(NativeOrEncoded::Native(Some(Vec::new())))
 	}
+
+	fn ParachainHost_signing_context_runtime_api_impl(
+		&self,
+		_at: &BlockId,
+		_: ExecutionContext,
+		_: Option<()>,
+		_: Vec<u8>,
+	) -> ClientResult<NativeOrEncoded<SigningContext>> {
+		Ok(NativeOrEncoded::Native(
+				SigningContext {
+					session_index: Default::default(),
+					parent_hash: Default::default(),
+				}
+			)
+		)
+	}
 }
 
 impl super::Service {
@@ -389,11 +404,15 @@ fn consensus_instances_cleaned_up() {
 	let relay_parent = [0; 32].into();
 	let authorities = Vec::new();
 
+	let signing_context = SigningContext {
+		session_index: Default::default(),
+		parent_hash: relay_parent,
+	};
 	let table = Arc::new(SharedTable::new(
 		Vec::new(),
 		HashMap::new(),
 		None,
-		relay_parent,
+		signing_context,
 		AvailabilityStore::new_in_memory(service.clone()),
 		None,
 	));

polkadot/primitives/Cargo.toml

@@ -13,6 +13,7 @@ application-crypto = { package = "sp-application-crypto", git = "https://github.
 sp-api = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-version = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-std = { package = "sp-std", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-staking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 runtime_primitives = { package = "sp-runtime", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 polkadot-parachain = { path = "../parachain", default-features = false }
 trie = { package = "sp-trie", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -33,6 +34,7 @@ std = [
 	"sp-api/std",
 	"sp-std/std",
 	"sp-version/std",
+	"sp-staking/std",
 	"runtime_primitives/std",
 	"serde",
 	"polkadot-parachain/std",

polkadot/primitives/src/parachain.rs

@@ -608,6 +608,15 @@ pub enum ValidityAttestation {
 	Explicit(ValidatorSignature),
 }
 
+/// A type returned by runtime with current session index and a parent hash.
+#[derive(Clone, Eq, PartialEq, Default, Decode, Encode, RuntimeDebug)]
+pub struct SigningContext {
+	/// Current session index.
+	pub session_index: sp_staking::SessionIndex,
+	/// Hash of the parent.
+	pub parent_hash: Hash,
+}
+
 /// An attested candidate. This is submitted to the relay chain by a block author.
 #[derive(Clone, PartialEq, Decode, Encode, RuntimeDebug)]
 pub struct AttestedCandidate {
@@ -655,7 +664,7 @@ impl FeeSchedule {
 
 sp_api::decl_runtime_apis! {
 	/// The API for querying the state of parachains on-chain.
-	#[api_version(2)]
+	#[api_version(3)]
 	pub trait ParachainHost {
 		/// Get the current validators.
 		fn validators() -> Vec<ValidatorId>;
@@ -673,6 +682,8 @@ sp_api::decl_runtime_apis! {
 		/// Extract the abridged head that was set in the extrinsics.
 		fn get_heads(extrinsics: Vec<<Block as BlockT>::Extrinsic>)
 			-> Option<Vec<AbridgedCandidateReceipt>>;
+		/// Get a `SigningContext` with current `SessionIndex` and parent hash.
+		fn signing_context() -> SigningContext;
 	}
 }
 

polkadot/runtime/common/src/parachains.rs

@@ -44,7 +44,7 @@ use primitives::{
 		UpwardMessage, ValidatorId, ActiveParas, CollatorId, Retriable, OmittedValidationData,
 		CandidateReceipt, GlobalValidationSchedule, AbridgedCandidateReceipt,
 		LocalValidationData, ValidityAttestation, NEW_HEADS_IDENTIFIER, PARACHAIN_KEY_TYPE_ID,
-		ValidatorSignature,
+		ValidatorSignature, SigningContext,
 	},
 };
 use frame_support::{
@@ -121,7 +121,7 @@ pub struct ValidatorIdentities<T>(sp_std::marker::PhantomData<T>);
 /// `Hash` - a type of a hash used in the runtime.
 #[derive(RuntimeDebug, Encode, Decode)]
 #[derive(Clone, Eq, PartialEq)]
-pub struct DoubleVoteReport<Proof, Hash> {
+pub struct DoubleVoteReport<Proof> {
 	/// Identity of the double-voter.
 	pub identity: ValidatorId,
 	/// First vote of the double-vote.
@@ -130,11 +130,11 @@ pub struct DoubleVoteReport<Proof, Hash> {
 	pub second: (Statement, ValidatorSignature),
 	/// Proof that the validator with `identity` id was actually a validator at `parent_hash`.
 	pub proof: Proof,
-	/// Parent hash of the block this offence was commited.
-	pub parent_hash: Hash,
+	/// A `SigningContext` with a session and a parent hash of the moment this offence was commited.
+	pub signing_context: SigningContext,
 }
 
-impl<Proof: Parameter + GetSessionNumber, Hash: AsRef<[u8]>> DoubleVoteReport<Proof, Hash> {
+impl<Proof: Parameter + GetSessionNumber> DoubleVoteReport<Proof> {
 	fn verify<T: Trait<Proof = Proof>>(
 		&self,
 	) -> Result<(), DoubleVoteValidityError> {
@@ -145,9 +145,21 @@ impl<Proof: Parameter + GetSessionNumber, Hash: AsRef<[u8]>> DoubleVoteReport<Pr
 		T::KeyOwnerProofSystem::check_proof((PARACHAIN_KEY_TYPE_ID, id), self.proof.clone())
 			.ok_or(DoubleVoteValidityError::InvalidProof)?;
 
+		if self.proof.session() != self.signing_context.session_index {
+			return Err(DoubleVoteValidityError::InvalidReport);
+		}
+
 		// Check signatures.
-		Self::verify_vote(&first, &self.parent_hash, &self.identity)?;
-		Self::verify_vote(&second, &self.parent_hash, &self.identity)?;
+		Self::verify_vote(
+			&first,
+			&self.signing_context,
+			&self.identity,
+		)?;
+		Self::verify_vote(
+			&second,
+			&self.signing_context,
+			&self.identity,
+		)?;
 
 		match (&first.0, &second.0) {
 			// If issuing a `Candidate` message on a parachain block, neither a `Valid` or
@@ -173,10 +185,10 @@ impl<Proof: Parameter + GetSessionNumber, Hash: AsRef<[u8]>> DoubleVoteReport<Pr
 
 	fn verify_vote(
 		vote: &(Statement, ValidatorSignature),
-		parent_hash: &Hash,
+		signing_context: &SigningContext,
 		authority: &ValidatorId,
 	) -> Result<(), DoubleVoteValidityError> {
-		let payload = localized_payload(vote.0.clone(), parent_hash);
+		let payload = localized_payload(vote.0.clone(), signing_context);
 
 		if !vote.1.verify(&payload[..], authority) {
 			return Err(DoubleVoteValidityError::InvalidSignature);
@@ -203,7 +215,7 @@ impl GetSessionNumber for session::historical::Proof {
 	}
 }
 
-pub trait Trait: attestations::Trait + session::historical::Trait + staking::Trait {
+pub trait Trait: attestations::Trait + session::historical::Trait {
 	/// The outer origin type.
 	type Origin: From<Origin> + From<system::RawOrigin<Self::AccountId>>;
 
@@ -253,6 +265,9 @@ pub trait Trait: attestations::Trait + session::historical::Trait + staking::Tra
 		Self::IdentificationTuple,
 		DoubleVoteOffence<Self::IdentificationTuple>
 	>;
+
+	/// A type that converts the opaque hash type to exact one.
+	type BlockHashConversion: Convert<Self::Hash, primitives::Hash>;
 }
 
 /// Origin for the parachains module.
@@ -332,18 +347,6 @@ decl_storage! {
 		///
 		/// `None` if not yet updated.
 		pub DidUpdate: Option<Vec<ParaId>>;
-
-		/// The mapping from parent block hashes to session indexes.
-		///
-		/// Used for double vote report validation.
-		pub ParentToSessionIndex get(fn session_at_block):
-			map hasher(twox_64_concat) T::Hash => SessionIndex;
-
-		/// The era that is active currently.
-		///
-		/// Changes with the `ActiveEra` from `staking`. Upon these changes `ParentToSessionIndex`
-		/// is pruned.
-		ActiveEra get(fn active_era): Option<staking::EraIndex>;
 	}
 	add_extra_genesis {
 		config(authorities): Vec<ValidatorId>;
@@ -484,7 +487,6 @@ decl_module! {
 			origin,
 			report: DoubleVoteReport<
 				<T::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::Proof,
-				T::Hash,
 			>,
 		) -> DispatchResult {
 			let reporter = ensure_signed(origin)?;
@@ -519,26 +521,6 @@ decl_module! {
 		fn on_initialize() -> Weight {
 			<Self as Store>::DidUpdate::kill();
 
-			let current_session = <session::Module<T>>::current_index();
-			let parent_hash = <system::Module<T>>::parent_hash();
-
-			match Self::active_era() {
-				Some(era) => {
-					if let Some(active_era) = <staking::Module<T>>::current_era() {
-						if era != active_era {
-							<Self as Store>::ActiveEra::put(active_era);
-							<ParentToSessionIndex<T>>::remove_all();
-						}
-					}
-				}
-				None => {
-					if let Some(active_era) = <staking::Module<T>>::current_era() {
-						<Self as Store>::ActiveEra::set(Some(active_era));
-					}
-				}
-			}
-			<ParentToSessionIndex<T>>::insert(parent_hash, current_session);
-
 			SimpleDispatchInfo::default().weigh_data(())
 		}
 
@@ -552,9 +534,12 @@ fn majority_of(list_len: usize) -> usize {
 	list_len / 2 + list_len % 2
 }
 
-fn localized_payload<H: AsRef<[u8]>>(statement: Statement, parent_hash: H) -> Vec<u8> {
+fn localized_payload(
+	statement: Statement,
+	signing_context: &SigningContext,
+) -> Vec<u8> {
 	let mut encoded = statement.encode();
-	encoded.extend(parent_hash.as_ref());
+	signing_context.using_encoded(|s| encoded.extend(s));
 	encoded
 }
 
@@ -576,6 +561,17 @@ impl<T: Trait> Module<T> {
 		<Heads>::remove(id);
 	}
 
+	/// Get a `SigningContext` with a current `SessionIndex` and parent hash.
+	pub fn signing_context() -> SigningContext {
+		let session_index = <session::Module<T>>::current_index();
+		let parent_hash = <system::Module<T>>::parent_hash();
+
+		SigningContext {
+			session_index,
+			parent_hash: T::BlockHashConversion::convert(parent_hash),
+		}
+	}
+
 	/// Dispatch some messages from a parachain.
 	fn dispatch_message(
 		id: ParaId,
@@ -912,7 +908,8 @@ impl<T: Trait> Module<T> {
 		let sorted_validators = make_sorted_duties(&duty_roster.validator_duty);
 
 		let parent_hash = <system::Module<T>>::parent_hash();
-		let localized_payload = |statement: Statement| localized_payload(statement, parent_hash);
+		let signing_context = Self::signing_context();
+		let localized_payload = |statement: Statement| localized_payload(statement, &signing_context);
 
 		let mut validator_groups = GroupedDutyIter::new(&sorted_validators[..]);
 
@@ -1160,9 +1157,8 @@ impl<T: Trait + Send + Sync> SignedExtension for ValidateDoubleVoteReports<T> wh
 		if let Some(local_call) = call.is_sub_type() {
 			if let Call::report_double_vote(report) = local_call {
 				let validators = <session::Module<T>>::validators();
-				let parent_hash = report.parent_hash;
 
-				let expected_session = Module::<T>::session_at_block(parent_hash);
+				let expected_session = report.signing_context.session_index;
 				let session = report.proof.session();
 
 				if session != expected_session {
@@ -1467,6 +1463,7 @@ mod tests {
 		type Proof = <Historical as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::Proof;
 		type IdentificationTuple = <Self::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::IdentificationTuple;
 		type ReportOffence = Offences;
+		type BlockHashConversion = sp_runtime::traits::Identity;
 		type KeyOwnerProofSystem = Historical;
 	}
 
@@ -1559,7 +1556,7 @@ mod tests {
 	}
 
 	fn report_double_vote(
-		report: DoubleVoteReport<session::historical::Proof, <Test as system::Trait>::Hash>,
+		report: DoubleVoteReport<session::historical::Proof>,
 	) -> Result<ParachainsCall<Test>, TransactionValidityError> {
 		let inner = ParachainsCall::report_double_vote(report);
 		let call = Call::Parachains(inner.clone());
@@ -1604,7 +1601,6 @@ mod tests {
 
 	fn make_attestations(candidate: &mut AttestedCandidate) {
 		let mut vote_implicit = false;
-		let parent_hash = <system::Module<Test>>::parent_hash();
 
 		let (duty_roster, _) = Parachains::calculate_duty_roster();
 		let candidate_hash = candidate.candidate.hash();
@@ -1632,7 +1628,8 @@ mod tests {
 				Statement::Valid(candidate_hash.clone())
 			};
 
-			let payload = localized_payload(statement, parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload = localized_payload(statement, &signing_context);
 			let signature = key.sign(&payload[..]).into();
 
 			candidate.validity_votes.push(if vote_implicit {
@@ -2209,10 +2206,10 @@ mod tests {
 
 			let statement_candidate = Statement::Candidate(candidate_hash.clone());
 			let statement_valid = Statement::Valid(candidate_hash.clone());
-			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_candidate.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_valid.clone(), parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload_1 = localized_payload(statement_candidate.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_valid.clone(), &signing_context);
 
 			let signature_1 = key.sign(&payload_1[..]).into();
 			let signature_2 = key.sign(&payload_2[..]).into();
@@ -2240,7 +2237,7 @@ mod tests {
 				first: (statement_candidate, signature_1),
 				second: (statement_valid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			let inner = report_double_vote(report).unwrap();
@@ -2304,10 +2301,10 @@ mod tests {
 
 			let statement_candidate = Statement::Candidate(candidate_hash);
 			let statement_invalid = Statement::Invalid(candidate_hash.clone());
-			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_candidate.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_invalid.clone(), parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload_1 = localized_payload(statement_candidate.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_invalid.clone(), &signing_context);
 
 			let signature_1 = key.sign(&payload_1[..]).into();
 			let signature_2 = key.sign(&payload_2[..]).into();
@@ -2335,7 +2332,7 @@ mod tests {
 				first: (statement_candidate, signature_1),
 				second: (statement_invalid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			assert_ok!(Parachains::dispatch(
@@ -2401,10 +2398,10 @@ mod tests {
 
 			let statement_invalid = Statement::Invalid(candidate_hash.clone());
 			let statement_valid = Statement::Valid(candidate_hash.clone());
-			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_invalid.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_valid.clone(), parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload_1 = localized_payload(statement_invalid.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_valid.clone(), &signing_context);
 
 			let signature_1 = key.sign(&payload_1[..]).into();
 			let signature_2 = key.sign(&payload_2[..]).into();
@@ -2432,7 +2429,7 @@ mod tests {
 				first: (statement_invalid, signature_1),
 				second: (statement_valid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			assert_ok!(Parachains::dispatch(
@@ -2501,10 +2498,10 @@ mod tests {
 
 			let statement_candidate = Statement::Candidate(candidate_hash.clone());
 			let statement_valid = Statement::Valid(candidate_hash.clone());
-			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_candidate.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_valid.clone(), parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload_1 = localized_payload(statement_candidate.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_valid.clone(), &signing_context);
 
 			let signature_1 = key.sign(&payload_1[..]).into();
 			let signature_2 = key.sign(&payload_2[..]).into();
@@ -2532,7 +2529,7 @@ mod tests {
 				first: (statement_candidate, signature_1),
 				second: (statement_valid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			assert_ok!(Parachains::dispatch(
@@ -2609,10 +2606,10 @@ mod tests {
 
 			let statement_candidate = Statement::Candidate(candidate_hash.clone());
 			let statement_valid = Statement::Valid(candidate_hash.clone());
-			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_candidate.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_valid.clone(), parent_hash);
+			let signing_context = Parachains::signing_context();
+			let payload_1 = localized_payload(statement_candidate.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_valid.clone(), &signing_context);
 
 			let signature_1 = key_1.sign(&payload_1[..]).into();
 			let signature_2 = key_2.sign(&payload_2[..]).into();
@@ -2625,7 +2622,7 @@ mod tests {
 				first: (statement_candidate, signature_1),
 				second: (statement_valid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			assert_eq!(
@@ -2669,8 +2666,12 @@ mod tests {
 			let statement_valid = Statement::Valid(candidate_hash.clone());
 			let parent_hash = System::parent_hash();
 
-			let payload_1 = localized_payload(statement_candidate.clone(), parent_hash);
-			let payload_2 = localized_payload(statement_valid.clone(), parent_hash);
+			let signing_context = SigningContext {
+				session_index: Session::current_index() - 1,
+				parent_hash,
+			};
+			let payload_1 = localized_payload(statement_candidate.clone(), &signing_context);
+			let payload_2 = localized_payload(statement_valid.clone(), &signing_context);
 
 			let signature_1 = key.sign(&payload_1[..]).into();
 			let signature_2 = key.sign(&payload_2[..]).into();
@@ -2700,7 +2701,7 @@ mod tests {
 				first: (statement_candidate, signature_1),
 				second: (statement_valid, signature_2),
 				proof,
-				parent_hash,
+				signing_context,
 			};
 
 			assert!(report_double_vote(report.clone()).is_err());
@@ -2723,29 +2724,4 @@ mod tests {
 			}
 		});
 	}
-
-	#[test]
-	fn double_vote_hash_to_session_gets_pruned() {
-		let parachains = vec![
-			(1u32.into(), vec![], vec![]),
-		];
-
-		// Test that `ParentToSessionIndex` is pruned upon eras turn.
-		new_test_ext(parachains.clone()).execute_with(|| {
-			start_era(1);
-
-			let parent_hash_1 = System::parent_hash();
-			// The mapping should know about the session at this block.
-			assert_eq!(Parachains::session_at_block(parent_hash_1), 3);
-
-			start_era(2);
-
-			let parent_hash_2 = System::parent_hash();
-
-			// Info about a block from pevious era is removed.
-			assert_eq!(Parachains::session_at_block(parent_hash_1), 0);
-			// Info about a block form this era is present.
-			assert_eq!(Parachains::session_at_block(parent_hash_2), 6);
-		});
-	}
 }

polkadot/runtime/common/src/registrar.rs

@@ -827,6 +827,7 @@ mod tests {
 		type KeyOwnerProofSystem = session::historical::Module<Test>;
 		type IdentificationTuple = <Self::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::IdentificationTuple;
 		type ReportOffence = ();
+		type BlockHashConversion = sp_runtime::traits::Identity;
 	}
 
 	parameter_types! {
@@ -973,7 +974,7 @@ mod tests {
 		};
 		let (candidate, _) = candidate.abridge();
 		let candidate_hash = candidate.hash();
-		let payload = (Statement::Valid(candidate_hash), System::parent_hash()).encode();
+		let payload = (Statement::Valid(candidate_hash), session::Module::<Test>::current_index(), System::parent_hash()).encode();
 		let roster = Parachains::calculate_duty_roster().0.validator_duty;
 		AttestedCandidate {
 			candidate,

polkadot/runtime/kusama/src/lib.rs

@@ -25,7 +25,7 @@ use sp_core::u32_trait::{_1, _2, _3, _4, _5};
 use codec::{Encode, Decode};
 use primitives::{
 	AccountId, AccountIndex, Balance, BlockNumber, Hash, Nonce, Signature, Moment,
-	parachain::{self, ActiveParas, AbridgedCandidateReceipt}, ValidityError,
+	parachain::{self, ActiveParas, AbridgedCandidateReceipt, SigningContext}, ValidityError,
 };
 use runtime_common::{attestations, claims, parachains, registrar, slots,
 	impls::{CurrencyToVoteHandler, TargetedFeeAdjustment, ToAuthor},
@@ -496,6 +496,7 @@ impl parachains::Trait for Runtime {
 	type KeyOwnerProofSystem = session::historical::Module<Self>;
 	type IdentificationTuple = <Self::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::IdentificationTuple;
 	type ReportOffence = Offences;
+	type BlockHashConversion = sp_runtime::traits::Identity;
 }
 
 parameter_types! {
@@ -816,6 +817,9 @@ sp_api::impl_runtime_apis! {
 					Err(_) => None,
 				})
 		}
+		fn signing_context() -> SigningContext {
+			Parachains::signing_context()
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/runtime/polkadot/src/lib.rs

@@ -31,7 +31,7 @@ use sp_core::u32_trait::{_1, _2, _3, _4, _5};
 use codec::{Encode, Decode};
 use primitives::{
 	AccountId, AccountIndex, Balance, BlockNumber, Hash, Nonce, Signature, Moment,
-	parachain::{self, ActiveParas, AbridgedCandidateReceipt}, ValidityError,
+	parachain::{self, ActiveParas, AbridgedCandidateReceipt, SigningContext}, ValidityError,
 };
 use sp_runtime::{
 	create_runtime_str, generic, impl_opaque_keys,
@@ -504,6 +504,7 @@ impl parachains::Trait for Runtime {
 	type KeyOwnerProofSystem = session::historical::Module<Self>;
 	type IdentificationTuple = <Self::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>>::IdentificationTuple;
 	type ReportOffence = Offences;
+	type BlockHashConversion = sp_runtime::traits::Identity;
 }
 
 parameter_types! {
@@ -738,6 +739,9 @@ sp_api::impl_runtime_apis! {
 					Err(_) => None,
 				})
 		}
+		fn signing_context() -> SigningContext {
+			Parachains::signing_context()
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/runtime/test-runtime/src/lib.rs

@@ -24,7 +24,7 @@ use rstd::prelude::*;
 use codec::{Encode, Decode};
 use primitives::{
 	AccountId, AccountIndex, Balance, BlockNumber, Hash as HashT, Nonce, Signature, Moment,
-	parachain::{self, ActiveParas, AbridgedCandidateReceipt}, ValidityError,
+	parachain::{self, ActiveParas, AbridgedCandidateReceipt, SigningContext}, ValidityError,
 };
 use runtime_common::{attestations, claims, parachains, registrar, slots,
 	impls::{CurrencyToVoteHandler, TargetedFeeAdjustment},
@@ -319,6 +319,7 @@ impl parachains::Trait for Runtime {
 			Self::KeyOwnerProofSystem as KeyOwnerProofSystem<(KeyTypeId, Vec<u8>)>
 		>::IdentificationTuple;
 	type ReportOffence = Offences;
+	type BlockHashConversion = sp_runtime::traits::Identity;
 }
 
 impl offences::Trait for Runtime {
@@ -536,6 +537,9 @@ sp_api::impl_runtime_apis! {
 					Err(_) => None,
 				})
 		}
+		fn signing_context() -> SigningContext {
+			Parachains::signing_context()
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/validation/src/lib.rs

@@ -34,12 +34,11 @@ use std::{
 	sync::Arc,
 };
 use codec::Encode;
-use polkadot_primitives::Hash;
 use polkadot_primitives::parachain::{
 	Id as ParaId, Chain, DutyRoster, AbridgedCandidateReceipt,
 	Statement as PrimitiveStatement,
 	PoVBlock, ErasureChunk, ValidatorSignature, ValidatorIndex,
-	ValidatorPair, ValidatorId,
+	ValidatorPair, ValidatorId, SigningContext,
 };
 use primitives::Pair;
 
@@ -135,9 +134,13 @@ pub struct GroupInfo {
 /// Sign a table statement against a parent hash.
 /// The actual message signed is the encoded statement concatenated with the
 /// parent hash.
-pub fn sign_table_statement(statement: &Statement, key: &ValidatorPair, parent_hash: &Hash) -> ValidatorSignature {
+pub fn sign_table_statement(
+	statement: &Statement,
+	key: &ValidatorPair,
+	signing_context: &SigningContext,
+) -> ValidatorSignature {
 	let mut encoded = PrimitiveStatement::from(statement).encode();
-	encoded.extend(parent_hash.as_ref());
+	encoded.extend(signing_context.encode());
 
 	key.sign(&encoded)
 }
@@ -147,12 +150,12 @@ pub fn check_statement(
 	statement: &Statement,
 	signature: &ValidatorSignature,
 	signer: ValidatorId,
-	parent_hash: &Hash,
+	signing_context: &SigningContext,
 ) -> bool {
 	use runtime_primitives::traits::AppVerify;
 
 	let mut encoded = PrimitiveStatement::from(statement).encode();
-	encoded.extend(parent_hash.as_ref());
+	encoded.extend(signing_context.encode());
 
 	signature.verify(&encoded[..], &signer)
 }
@@ -214,11 +217,19 @@ mod tests {
 	fn sign_and_check_statement() {
 		let statement: Statement = GenericStatement::Valid([1; 32].into());
 		let parent_hash = [2; 32].into();
+		let signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash,
+		};
 
-		let sig = sign_table_statement(&statement, &Sr25519Keyring::Alice.pair().into(), &parent_hash);
+		let sig = sign_table_statement(&statement, &Sr25519Keyring::Alice.pair().into(), &signing_context);
 
-		assert!(check_statement(&statement, &sig, Sr25519Keyring::Alice.public().into(), &parent_hash));
-		assert!(!check_statement(&statement, &sig, Sr25519Keyring::Alice.public().into(), &[0xff; 32].into()));
-		assert!(!check_statement(&statement, &sig, Sr25519Keyring::Bob.public().into(), &parent_hash));
+		let wrong_signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash: [0xff; 32].into(),
+		};
+		assert!(check_statement(&statement, &sig, Sr25519Keyring::Alice.public().into(), &signing_context));
+		assert!(!check_statement(&statement, &sig, Sr25519Keyring::Alice.public().into(), &wrong_signing_context));
+		assert!(!check_statement(&statement, &sig, Sr25519Keyring::Bob.public().into(), &signing_context));
 	}
 }

polkadot/validation/src/shared_table/mod.rs

@@ -25,7 +25,7 @@ use table::{self, Table, Context as TableContextTrait};
 use polkadot_primitives::{Block, Hash};
 use polkadot_primitives::parachain::{
 	Id as ParaId, AbridgedCandidateReceipt, ValidatorPair, ValidatorId,
-	AttestedCandidate, ParachainHost, PoVBlock, ValidatorIndex,
+	AttestedCandidate, ParachainHost, PoVBlock, ValidatorIndex, SigningContext,
 };
 
 use parking_lot::Mutex;
@@ -48,7 +48,7 @@ pub use table::{SignedStatement, Statement};
 pub use table::generic::Statement as GenericStatement;
 
 struct TableContext {
-	parent_hash: Hash,
+	signing_context: SigningContext,
 	key: Option<Arc<ValidatorPair>>,
 	groups: HashMap<ParaId, GroupInfo>,
 	validators: Vec<ValidatorId>,
@@ -87,7 +87,12 @@ impl TableContext {
 	fn sign_statement(&self, statement: table::Statement) -> Option<table::SignedStatement> {
 		self.local_index().and_then(move |sender|
 			self.key.as_ref()
-				.map(|key| crate::sign_table_statement(&statement, key, &self.parent_hash).into())
+				.map(|key| crate::sign_table_statement(
+						&statement,
+						key,
+						&self.signing_context,
+					).into()
+				)
 				.map(move |signature| table::SignedStatement { statement, signature, sender })
 		)
 	}
@@ -189,7 +194,7 @@ impl SharedTableInner {
 
 		work.map(|work| ParachainWork {
 			availability_store: self.availability_store.clone(),
-			relay_parent: context.parent_hash.clone(),
+			relay_parent: context.signing_context.parent_hash.clone(),
 			work,
 			max_block_data_size,
 			n_validators: context.validators.len(),
@@ -408,12 +413,12 @@ impl SharedTable {
 		validators: Vec<ValidatorId>,
 		groups: HashMap<ParaId, GroupInfo>,
 		key: Option<Arc<ValidatorPair>>,
-		parent_hash: Hash,
+		signing_context: SigningContext,
 		availability_store: AvailabilityStore,
 		max_block_data_size: Option<u64>,
 	) -> Self {
 		SharedTable {
-			context: Arc::new(TableContext { groups, key, parent_hash, validators: validators.clone(), }),
+			context: Arc::new(TableContext { groups, key, signing_context, validators: validators.clone(), }),
 			max_block_data_size,
 			inner: Arc::new(Mutex::new(SharedTableInner {
 				table: Table::default(),
@@ -425,8 +430,8 @@ impl SharedTable {
 	}
 
 	/// Get the parent hash this table should hold statements localized to.
-	pub fn consensus_parent_hash(&self) -> &Hash {
-		&self.context.parent_hash
+	pub fn signing_context(&self) -> &SigningContext {
+		&self.context.signing_context
 	}
 
 	/// Get the local validator session key.
@@ -654,7 +659,11 @@ mod tests {
 		let mut groups = HashMap::new();
 
 		let para_id = ParaId::from(1);
-		let parent_hash = Default::default();
+		let parent_hash = Hash::default();
+		let signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash: parent_hash.clone(),
+		};
 
 		let local_key = Sr25519Keyring::Alice.pair();
 		let local_id: ValidatorId = local_key.public().into();
@@ -673,7 +682,7 @@ mod tests {
 			[local_id, validity_other].to_vec(),
 			groups,
 			Some(local_key.clone()),
-			parent_hash,
+			signing_context.clone(),
 			AvailabilityStore::new_in_memory(DummyErasureNetworking),
 			None,
 		);
@@ -684,7 +693,11 @@ mod tests {
 
 		let candidate_statement = GenericStatement::Candidate(candidate);
 
-		let signature = crate::sign_table_statement(&candidate_statement, &validity_other_key.into(), &parent_hash);
+		let signature = crate::sign_table_statement(
+			&candidate_statement,
+			&validity_other_key.into(),
+			&signing_context,
+		);
 		let signed_statement = ::table::generic::SignedStatement {
 			statement: candidate_statement,
 			signature: signature.into(),
@@ -702,7 +715,11 @@ mod tests {
 		let mut groups = HashMap::new();
 
 		let para_id = ParaId::from(1);
-		let parent_hash = Default::default();
+		let parent_hash = Hash::default();
+		let signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash: parent_hash.clone(),
+		};
 
 		let local_key = Sr25519Keyring::Alice.pair();
 		let local_id: ValidatorId = local_key.public().into();
@@ -721,7 +738,7 @@ mod tests {
 			[local_id, validity_other].to_vec(),
 			groups,
 			Some(local_key.clone()),
-			parent_hash,
+			signing_context.clone(),
 			AvailabilityStore::new_in_memory(DummyErasureNetworking),
 			None,
 		);
@@ -732,7 +749,11 @@ mod tests {
 
 		let candidate_statement = GenericStatement::Candidate(candidate);
 
-		let signature = crate::sign_table_statement(&candidate_statement, &validity_other_key.into(), &parent_hash);
+		let signature = crate::sign_table_statement(
+			&candidate_statement,
+			&validity_other_key.into(),
+			&signing_context,
+		);
 		let signed_statement = ::table::generic::SignedStatement {
 			statement: candidate_statement,
 			signature: signature.into(),
@@ -874,7 +895,11 @@ mod tests {
 		let mut groups = HashMap::new();
 
 		let para_id = ParaId::from(1);
-		let parent_hash = Default::default();
+		let parent_hash = Hash::default();
+		let signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash: parent_hash.clone(),
+		};
 
 		let local_key = Sr25519Keyring::Alice.pair();
 		let local_id: ValidatorId = local_key.public().into();
@@ -893,7 +918,7 @@ mod tests {
 			[local_id, validity_other].to_vec(),
 			groups,
 			Some(local_key.clone()),
-			parent_hash,
+			signing_context.clone(),
 			AvailabilityStore::new_in_memory(DummyErasureNetworking),
 			None,
 		);
@@ -905,7 +930,11 @@ mod tests {
 		let candidate_hash = candidate.hash();
 		let candidate_statement = GenericStatement::Candidate(candidate);
 
-		let signature = crate::sign_table_statement(&candidate_statement, &validity_other_key.into(), &parent_hash);
+		let signature = crate::sign_table_statement(
+			&candidate_statement,
+			&validity_other_key.into(),
+			&signing_context,
+		);
 		let signed_statement = ::table::generic::SignedStatement {
 			statement: candidate_statement,
 			signature: signature.into(),
@@ -934,7 +963,11 @@ mod tests {
 
 		let para_id = ParaId::from(1);
 		let pov_block = pov_block_with_data(vec![1, 2, 3]);
-		let parent_hash = Default::default();
+		let parent_hash = Hash::default();
+		let signing_context = SigningContext {
+			session_index: Default::default(),
+			parent_hash: parent_hash.clone(),
+		};
 
 		let local_key = Sr25519Keyring::Alice.pair();
 		let local_id: ValidatorId = local_key.public().into();
@@ -952,7 +985,7 @@ mod tests {
 			[local_id, validity_other].to_vec(),
 			groups,
 			Some(local_key.clone()),
-			parent_hash,
+			signing_context.clone(),
 			AvailabilityStore::new_in_memory(DummyErasureNetworking),
 			None,
 		);

polkadot/validation/src/validation_service/mod.rs

@@ -36,7 +36,7 @@ use consensus::SelectChain;
 use futures::{future::ready, prelude::*, task::{Spawn, SpawnExt}};
 use polkadot_primitives::{Block, Hash, BlockId};
 use polkadot_primitives::parachain::{
-	Chain, ParachainHost, Id as ParaId, ValidatorIndex, ValidatorId, ValidatorPair,
+	Chain, ParachainHost, Id as ParaId, ValidatorIndex, ValidatorId, ValidatorPair, SigningContext,
 };
 use babe_primitives::BabeApi;
 use keystore::KeyStorePtr;
@@ -44,7 +44,7 @@ use sp_api::{ApiExt, ProvideRuntimeApi};
 use runtime_primitives::traits::HashFor;
 use availability_store::Store as AvailabilityStore;
 
-use log::{warn, error, info, debug};
+use log::{warn, error, info, debug, trace};
 
 use super::{Network, Collators, SharedTable, TableRouter};
 use crate::Error;
@@ -334,11 +334,29 @@ impl<C, N, P, SP> ParachainValidationInstances<C, N, P, SP> where
 			}
 		}
 
+		let api = self.client.runtime_api();
+
+		let signing_context = if api.has_api_with::<dyn ParachainHost<Block, Error = ()>, _>(
+			&BlockId::hash(parent_hash),
+			|version| version >= 3,
+		)? {
+			api.signing_context(&id)?
+		} else {
+			trace!(
+				target: "validation",
+				"Expected runtime with ParachainHost version >= 3",
+			);
+			SigningContext {
+				session_index: 0,
+				parent_hash,
+			}
+		};
+
 		let table = Arc::new(SharedTable::new(
 			validators.clone(),
 			group_info,
 			sign_with,
-			parent_hash,
+			signing_context,
 			self.availability_store.clone(),
 			max_block_data_size,
 		));