Gloas add process_payload_attestation (#8286)

* process_payload_attestation implemented per eip-7732

* allow duplicates in indexed payload attestation indices

* updates per pr review

beacon_node/store/src/consensus_context.rs

@@ -35,6 +35,8 @@ impl<E: EthSpec> OnDiskConsensusContext<E> {
             proposer_index,
             current_block_root,
             indexed_attestations,
+            indexed_payload_attestations: _,
+            // TODO(EIP-7732): add indexed_payload_attestations to the on-disk format.
         } = ctxt;
         OnDiskConsensusContext {
             slot,

consensus/state_processing/src/common/get_payload_attesting_indices.rs

@@ -0,0 +1,43 @@
+use crate::per_block_processing::errors::{
+    BlockOperationError, PayloadAttestationInvalid as Invalid,
+};
+use types::*;
+
+pub fn get_indexed_payload_attestation<E: EthSpec>(
+    state: &BeaconState<E>,
+    slot: Slot,
+    payload_attestation: &PayloadAttestation<E>,
+    spec: &ChainSpec,
+) -> Result<IndexedPayloadAttestation<E>, BlockOperationError<Invalid>> {
+    let attesting_indices = get_payload_attesting_indices(state, slot, payload_attestation, spec)?;
+
+    Ok(IndexedPayloadAttestation {
+        attesting_indices: VariableList::new(attesting_indices)?,
+        data: payload_attestation.data.clone(),
+        signature: payload_attestation.signature.clone(),
+    })
+}
+
+pub fn get_payload_attesting_indices<E: EthSpec>(
+    state: &BeaconState<E>,
+    slot: Slot,
+    payload_attestation: &PayloadAttestation<E>,
+    spec: &ChainSpec,
+) -> Result<Vec<u64>, BeaconStateError> {
+    let ptc = state.get_ptc(slot, spec)?;
+
+    let bitlist = &payload_attestation.aggregation_bits;
+    if bitlist.len() != E::PTCSize::to_usize() {
+        return Err(BeaconStateError::InvalidBitfield);
+    }
+
+    let mut attesting_indices = Vec::<u64>::new();
+    for (i, index) in ptc.into_iter().enumerate() {
+        if let Ok(true) = bitlist.get(i) {
+            attesting_indices.push(index as u64);
+        }
+    }
+    attesting_indices.sort_unstable();
+
+    Ok(attesting_indices)
+}

consensus/state_processing/src/common/mod.rs

@@ -1,6 +1,7 @@
 mod deposit_data_tree;
 mod get_attestation_participation;
 mod get_attesting_indices;
+mod get_payload_attesting_indices;
 mod initiate_validator_exit;
 mod slash_validator;
 
@@ -13,6 +14,9 @@ pub use get_attestation_participation::get_attestation_participation_flag_indice
 pub use get_attesting_indices::{
     attesting_indices_base, attesting_indices_electra, get_attesting_indices_from_state,
 };
+pub use get_payload_attesting_indices::{
+    get_indexed_payload_attestation, get_payload_attesting_indices,
+};
 pub use initiate_validator_exit::initiate_validator_exit;
 pub use slash_validator::slash_validator;
 

consensus/state_processing/src/consensus_context.rs

@@ -1,11 +1,16 @@
 use crate::EpochCacheError;
-use crate::common::{attesting_indices_base, attesting_indices_electra};
-use crate::per_block_processing::errors::{AttestationInvalid, BlockOperationError};
+use crate::common::{
+    attesting_indices_base, attesting_indices_electra, get_indexed_payload_attestation,
+};
+use crate::per_block_processing::errors::{
+    AttestationInvalid, BlockOperationError, PayloadAttestationInvalid,
+};
 use std::collections::{HashMap, hash_map::Entry};
 use tree_hash::TreeHash;
 use types::{
     AbstractExecPayload, AttestationRef, BeaconState, BeaconStateError, ChainSpec, Epoch, EthSpec,
-    Hash256, IndexedAttestation, IndexedAttestationRef, SignedBeaconBlock, Slot,
+    Hash256, IndexedAttestation, IndexedAttestationRef, IndexedPayloadAttestation,
+    PayloadAttestation, SignedBeaconBlock, Slot,
 };
 
 #[derive(Debug, PartialEq, Clone)]
@@ -22,6 +27,8 @@ pub struct ConsensusContext<E: EthSpec> {
     pub current_block_root: Option<Hash256>,
     /// Cache of indexed attestations constructed during block processing.
     pub indexed_attestations: HashMap<Hash256, IndexedAttestation<E>>,
+    /// Cache of indexed payload attestations constructed during block processing.
+    pub indexed_payload_attestations: HashMap<Hash256, IndexedPayloadAttestation<E>>,
 }
 
 #[derive(Debug, PartialEq, Clone)]
@@ -55,6 +62,7 @@ impl<E: EthSpec> ConsensusContext<E> {
             proposer_index: None,
             current_block_root: None,
             indexed_attestations: HashMap::new(),
+            indexed_payload_attestations: HashMap::new(),
         }
     }
 
@@ -177,6 +185,25 @@ impl<E: EthSpec> ConsensusContext<E> {
         .map(|indexed_attestation| (*indexed_attestation).to_ref())
     }
 
+    pub fn get_indexed_payload_attestation<'a>(
+        &'a mut self,
+        state: &BeaconState<E>,
+        slot: Slot,
+        payload_attestation: &'a PayloadAttestation<E>,
+        spec: &ChainSpec,
+    ) -> Result<&'a IndexedPayloadAttestation<E>, BlockOperationError<PayloadAttestationInvalid>>
+    {
+        let key = payload_attestation.tree_hash_root();
+        match self.indexed_payload_attestations.entry(key) {
+            Entry::Occupied(occupied) => Ok(occupied.into_mut()),
+            Entry::Vacant(vacant) => {
+                let indexed_payload_attestation =
+                    get_indexed_payload_attestation(state, slot, payload_attestation, spec)?;
+                Ok(vacant.insert(indexed_payload_attestation))
+            }
+        }
+    }
+
     pub fn num_cached_indexed_attestations(&self) -> usize {
         self.indexed_attestations.len()
     }

consensus/state_processing/src/per_block_processing.rs

@@ -18,6 +18,7 @@ pub use self::verify_proposer_slashing::verify_proposer_slashing;
 pub use altair::sync_committee::process_sync_aggregate;
 pub use block_signature_verifier::{BlockSignatureVerifier, ParallelSignatureSets};
 pub use is_valid_indexed_attestation::is_valid_indexed_attestation;
+pub use is_valid_indexed_payload_attestation::is_valid_indexed_payload_attestation;
 pub use process_operations::process_operations;
 pub use verify_attestation::{
     verify_attestation_for_block_inclusion, verify_attestation_for_state,
@@ -33,6 +34,7 @@ pub mod block_signature_verifier;
 pub mod deneb;
 pub mod errors;
 mod is_valid_indexed_attestation;
+mod is_valid_indexed_payload_attestation;
 pub mod process_operations;
 pub mod process_withdrawals;
 pub mod signature_sets;
@@ -42,6 +44,7 @@ mod verify_attester_slashing;
 mod verify_bls_to_execution_change;
 mod verify_deposit;
 mod verify_exit;
+mod verify_payload_attestation;
 mod verify_proposer_slashing;
 
 use crate::common::update_progressive_balances_cache::{

consensus/state_processing/src/per_block_processing/errors.rs

@@ -41,6 +41,10 @@ pub enum BlockProcessingError {
         index: usize,
         reason: AttestationInvalid,
     },
+    PayloadAttestationInvalid {
+        index: usize,
+        reason: PayloadAttestationInvalid,
+    },
     DepositInvalid {
         index: usize,
         reason: DepositInvalid,
@@ -209,7 +213,8 @@ impl_into_block_processing_error_with_index!(
     AttestationInvalid,
     DepositInvalid,
     ExitInvalid,
-    BlsExecutionChangeInvalid
+    BlsExecutionChangeInvalid,
+    PayloadAttestationInvalid
 );
 
 pub type HeaderValidationError = BlockOperationError<HeaderInvalid>;
@@ -410,6 +415,58 @@ pub enum IndexedAttestationInvalid {
     SignatureSetError(SignatureSetError),
 }
 
+#[derive(Debug, PartialEq, Clone)]
+pub enum PayloadAttestationInvalid {
+    /// Block root does not match the parent beacon block root.
+    BlockRootMismatch {
+        expected: Hash256,
+        found: Hash256,
+    },
+    /// The attestation slot is not the previous slot.
+    SlotMismatch {
+        expected: Slot,
+        found: Slot,
+    },
+    BadIndexedPayloadAttestation(IndexedPayloadAttestationInvalid),
+}
+
+impl From<BlockOperationError<IndexedPayloadAttestationInvalid>>
+    for BlockOperationError<PayloadAttestationInvalid>
+{
+    fn from(e: BlockOperationError<IndexedPayloadAttestationInvalid>) -> Self {
+        match e {
+            BlockOperationError::Invalid(e) => BlockOperationError::invalid(
+                PayloadAttestationInvalid::BadIndexedPayloadAttestation(e),
+            ),
+            BlockOperationError::BeaconStateError(e) => BlockOperationError::BeaconStateError(e),
+            BlockOperationError::SignatureSetError(e) => BlockOperationError::SignatureSetError(e),
+            BlockOperationError::SszTypesError(e) => BlockOperationError::SszTypesError(e),
+            BlockOperationError::BitfieldError(e) => BlockOperationError::BitfieldError(e),
+            BlockOperationError::ConsensusContext(e) => BlockOperationError::ConsensusContext(e),
+            BlockOperationError::ArithError(e) => BlockOperationError::ArithError(e),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum IndexedPayloadAttestationInvalid {
+    /// The number of indices is 0.
+    IndicesEmpty,
+    /// The validator indices were not in increasing order.
+    ///
+    /// The error occurred between the given `index` and `index + 1`
+    BadValidatorIndicesOrdering(usize),
+    /// The validator index is unknown. One cannot slash one who does not exist.
+    UnknownValidator(u64),
+    /// The indexed attestation aggregate signature was not valid.
+    BadSignature,
+    /// There was an error whilst attempting to get a set of signatures. The signatures may have
+    /// been invalid or an internal error occurred.
+    SignatureSetError(SignatureSetError),
+    /// Invalid Payload Status
+    PayloadStatusInvalid,
+}
+
 #[derive(Debug, PartialEq, Clone)]
 pub enum DepositInvalid {
     /// The signature (proof-of-possession) does not match the given pubkey.

consensus/state_processing/src/per_block_processing/is_valid_indexed_payload_attestation.rs

@@ -0,0 +1,50 @@
+use super::errors::{BlockOperationError, IndexedPayloadAttestationInvalid as Invalid};
+use super::signature_sets::{get_pubkey_from_state, indexed_payload_attestation_signature_set};
+use crate::VerifySignatures;
+use itertools::Itertools;
+use types::*;
+
+fn error(reason: Invalid) -> BlockOperationError<Invalid> {
+    BlockOperationError::invalid(reason)
+}
+
+pub fn is_valid_indexed_payload_attestation<E: EthSpec>(
+    state: &BeaconState<E>,
+    indexed_payload_attestation: &IndexedPayloadAttestation<E>,
+    verify_signatures: VerifySignatures,
+    spec: &ChainSpec,
+) -> Result<(), BlockOperationError<Invalid>> {
+    // Verify indices are non-empty and sorted (duplicates allowed)
+    let indices = &indexed_payload_attestation.attesting_indices;
+    verify!(!indices.is_empty(), Invalid::IndicesEmpty);
+    let check_sorted = |list: &[u64]| -> Result<(), BlockOperationError<Invalid>> {
+        list.iter()
+            .tuple_windows()
+            .enumerate()
+            .try_for_each(|(i, (x, y))| {
+                if x <= y {
+                    Ok(())
+                } else {
+                    Err(error(Invalid::BadValidatorIndicesOrdering(i)))
+                }
+            })?;
+        Ok(())
+    };
+    check_sorted(indices)?;
+
+    if verify_signatures.is_true() {
+        verify!(
+            indexed_payload_attestation_signature_set(
+                state,
+                |i| get_pubkey_from_state(state, i),
+                &indexed_payload_attestation.signature,
+                indexed_payload_attestation,
+                spec
+            )?
+            .verify(),
+            Invalid::BadSignature
+        );
+    }
+
+    Ok(())
+}

consensus/state_processing/src/per_block_processing/process_operations.rs

@@ -5,6 +5,7 @@ use crate::common::{
     slash_validator,
 };
 use crate::per_block_processing::errors::{BlockProcessingError, IntoWithIndex};
+use crate::per_block_processing::verify_payload_attestation::verify_payload_attestation;
 use types::consts::altair::{PARTICIPATION_FLAG_WEIGHTS, PROPOSER_WEIGHT, WEIGHT_DENOMINATOR};
 use types::typenum::U33;
 
@@ -37,7 +38,15 @@ pub fn process_operations<E: EthSpec, Payload: AbstractExecPayload<E>>(
         process_bls_to_execution_changes(state, bls_to_execution_changes, verify_signatures, spec)?;
     }
 
-    if state.fork_name_unchecked().electra_enabled() {
+    if state.fork_name_unchecked().gloas_enabled() {
+        process_payload_attestations(
+            state,
+            block_body.payload_attestations()?.iter(),
+            verify_signatures,
+            ctxt,
+            spec,
+        )?;
+    } else if state.fork_name_unchecked().electra_enabled() {
         state.update_pubkey_cache()?;
         process_deposit_requests(state, &block_body.execution_requests()?.deposits, spec)?;
         process_withdrawal_requests(state, &block_body.execution_requests()?.withdrawals, spec)?;
@@ -789,3 +798,52 @@ pub fn process_consolidation_request<E: EthSpec>(
 
     Ok(())
 }
+
+// TODO(EIP-7732): Add test cases for `process_payload_attestations` to
+// `consensus/state_processing/src/per_block_processing/tests.rs`.
+// The tests will require being able to build Gloas blocks with PayloadAttestations,
+// which currently fails due to incomplete Gloas block structure as mentioned here
+// https://github.com/sigp/lighthouse/pull/8273
+pub fn process_payload_attestation<E: EthSpec>(
+    state: &mut BeaconState<E>,
+    payload_attestation: &PayloadAttestation<E>,
+    att_index: usize,
+    verify_signatures: VerifySignatures,
+    ctxt: &mut ConsensusContext<E>,
+    spec: &ChainSpec,
+) -> Result<(), BlockProcessingError> {
+    verify_payload_attestation(state, payload_attestation, ctxt, verify_signatures, spec)
+        .map_err(|e| e.into_with_index(att_index))
+}
+
+pub fn process_payload_attestations<'a, E: EthSpec, I>(
+    state: &mut BeaconState<E>,
+    payload_attestations: I,
+    verify_signatures: VerifySignatures,
+    ctxt: &mut ConsensusContext<E>,
+    spec: &ChainSpec,
+) -> Result<(), BlockProcessingError>
+where
+    I: Iterator<Item = &'a PayloadAttestation<E>>,
+{
+    // Ensure required caches are all built. These should be no-ops during regular operation.
+    // TODO(EIP-7732): verify necessary caches
+    state.build_committee_cache(RelativeEpoch::Current, spec)?;
+    state.build_committee_cache(RelativeEpoch::Previous, spec)?;
+    initialize_epoch_cache(state, spec)?;
+    initialize_progressive_balances_cache(state, spec)?;
+    state.build_slashings_cache()?;
+
+    payload_attestations
+        .enumerate()
+        .try_for_each(|(i, payload_attestation)| {
+            process_payload_attestation(
+                state,
+                payload_attestation,
+                i,
+                verify_signatures,
+                ctxt,
+                spec,
+            )
+        })
+}

consensus/state_processing/src/per_block_processing/signature_sets.rs

@@ -9,11 +9,12 @@ use tree_hash::TreeHash;
 use types::{
     AbstractExecPayload, AggregateSignature, AttesterSlashingRef, BeaconBlockRef, BeaconState,
     BeaconStateError, ChainSpec, DepositData, Domain, Epoch, EthSpec, Fork, Hash256,
-    InconsistentFork, IndexedAttestation, IndexedAttestationRef, ProposerSlashing, PublicKey,
-    PublicKeyBytes, Signature, SignedAggregateAndProof, SignedBeaconBlock, SignedBeaconBlockHeader,
-    SignedBlsToExecutionChange, SignedContributionAndProof, SignedExecutionPayloadBid,
-    SignedExecutionPayloadEnvelope, SignedRoot, SignedVoluntaryExit, SigningData, Slot,
-    SyncAggregate, SyncAggregatorSelectionData, Unsigned,
+    InconsistentFork, IndexedAttestation, IndexedAttestationRef, IndexedPayloadAttestation,
+    ProposerSlashing, PublicKey, PublicKeyBytes, Signature, SignedAggregateAndProof,
+    SignedBeaconBlock, SignedBeaconBlockHeader, SignedBlsToExecutionChange,
+    SignedContributionAndProof, SignedExecutionPayloadBid, SignedExecutionPayloadEnvelope,
+    SignedRoot, SignedVoluntaryExit, SigningData, Slot, SyncAggregate, SyncAggregatorSelectionData,
+    Unsigned,
 };
 
 pub type Result<T> = std::result::Result<T, Error>;
@@ -299,6 +300,35 @@ where
     Ok(SignatureSet::multiple_pubkeys(signature, pubkeys, message))
 }
 
+pub fn indexed_payload_attestation_signature_set<'a, 'b, E, F>(
+    state: &'a BeaconState<E>,
+    get_pubkey: F,
+    signature: &'a AggregateSignature,
+    indexed_payload_attestation: &'b IndexedPayloadAttestation<E>,
+    spec: &'a ChainSpec,
+) -> Result<SignatureSet<'a>>
+where
+    E: EthSpec,
+    F: Fn(usize) -> Option<Cow<'a, PublicKey>>,
+{
+    let mut pubkeys = Vec::with_capacity(indexed_payload_attestation.attesting_indices.len());
+    for &validator_idx in indexed_payload_attestation.attesting_indices.iter() {
+        pubkeys.push(
+            get_pubkey(validator_idx as usize).ok_or(Error::ValidatorUnknown(validator_idx))?,
+        );
+    }
+
+    let domain = spec.compute_domain(
+        Domain::PTCAttester,
+        spec.genesis_fork_version,
+        state.genesis_validators_root(),
+    );
+
+    let message = indexed_payload_attestation.data.signing_root(domain);
+
+    Ok(SignatureSet::multiple_pubkeys(signature, pubkeys, message))
+}
+
 /// Returns the signature set for the given `indexed_attestation` but pubkeys are supplied directly
 /// instead of from the state.
 pub fn indexed_attestation_signature_set_from_pubkeys<'a, 'b, E, F>(

consensus/state_processing/src/per_block_processing/verify_payload_attestation.rs

@@ -0,0 +1,46 @@
+use super::VerifySignatures;
+use super::errors::{BlockOperationError, PayloadAttestationInvalid as Invalid};
+use crate::ConsensusContext;
+use crate::per_block_processing::is_valid_indexed_payload_attestation;
+use safe_arith::SafeArith;
+use types::*;
+
+pub fn verify_payload_attestation<'ctxt, E: EthSpec>(
+    state: &mut BeaconState<E>,
+    payload_attestation: &'ctxt PayloadAttestation<E>,
+    ctxt: &'ctxt mut ConsensusContext<E>,
+    verify_signatures: VerifySignatures,
+    spec: &ChainSpec,
+) -> Result<(), BlockOperationError<Invalid>> {
+    let data = &payload_attestation.data;
+
+    // Check that the attestation is for the parent beacon block
+    verify!(
+        data.beacon_block_root == state.latest_block_header().parent_root,
+        Invalid::BlockRootMismatch {
+            expected: state.latest_block_header().parent_root,
+            found: data.beacon_block_root,
+        }
+    );
+
+    // Check that the attestation is for the previous slot
+    verify!(
+        data.slot.safe_add(1)? == state.slot(),
+        Invalid::SlotMismatch {
+            expected: state.slot().saturating_sub(Slot::new(1)),
+            found: data.slot,
+        }
+    );
+
+    let indexed_payload_attestation =
+        ctxt.get_indexed_payload_attestation(state, data.slot, payload_attestation, spec)?;
+
+    is_valid_indexed_payload_attestation(
+        state,
+        indexed_payload_attestation,
+        verify_signatures,
+        spec,
+    )?;
+
+    Ok(())
+}

consensus/types/src/beacon_state.rs

@@ -188,6 +188,8 @@ pub enum Error {
     ProposerLookaheadOutOfBounds {
         i: usize,
     },
+    InvalidIndicesCount,
+    PleaseNotifyTheDevs(String),
 }
 
 /// Control whether an epoch-indexed field can be indexed at the next epoch or not.
@@ -1088,13 +1090,22 @@ impl<E: EthSpec> BeaconState<E> {
             }
         }
 
+        let gloas_enabled = self.fork_name_unchecked().gloas_enabled();
         epoch
             .slot_iter(E::slots_per_epoch())
             .map(|slot| {
                 let mut preimage = seed.to_vec();
                 preimage.append(&mut int_to_bytes8(slot.as_u64()));
                 let seed = hash(&preimage);
-                self.compute_proposer_index(indices, &seed, spec)
+
+                if gloas_enabled {
+                    self.compute_balance_weighted_selection(indices, &seed, 1, true, spec)?
+                        .first()
+                        .copied()
+                        .ok_or(Error::InsufficientValidators)
+                } else {
+                    self.compute_proposer_index(indices, &seed, spec)
+                }
             })
             .collect()
     }
@@ -1336,39 +1347,50 @@ impl<E: EthSpec> BeaconState<E> {
         let epoch = self.current_epoch().safe_add(1)?;
 
         let active_validator_indices = self.get_active_validator_indices(epoch, spec)?;
-        let active_validator_count = active_validator_indices.len();
-
         let seed = self.get_seed(epoch, Domain::SyncCommittee, spec)?;
-        let max_effective_balance = spec.max_effective_balance_for_fork(self.fork_name_unchecked());
-        let max_random_value = if self.fork_name_unchecked().electra_enabled() {
-            MAX_RANDOM_VALUE
-        } else {
-            MAX_RANDOM_BYTE
-        };
 
-        let mut i = 0;
-        let mut sync_committee_indices = Vec::with_capacity(E::SyncCommitteeSize::to_usize());
-        while sync_committee_indices.len() < E::SyncCommitteeSize::to_usize() {
-            let shuffled_index = compute_shuffled_index(
-                i.safe_rem(active_validator_count)?,
-                active_validator_count,
+        if self.fork_name_unchecked().gloas_enabled() {
+            self.compute_balance_weighted_selection(
+                &active_validator_indices,
                 seed.as_slice(),
-                spec.shuffle_round_count,
+                E::SyncCommitteeSize::to_usize(),
+                true,
+                spec,
             )
-            .ok_or(Error::UnableToShuffle)?;
-            let candidate_index = *active_validator_indices
-                .get(shuffled_index)
-                .ok_or(Error::ShuffleIndexOutOfBounds(shuffled_index))?;
-            let random_value = self.shuffling_random_value(i, seed.as_slice())?;
-            let effective_balance = self.get_validator(candidate_index)?.effective_balance;
-            if effective_balance.safe_mul(max_random_value)?
-                >= max_effective_balance.safe_mul(random_value)?
-            {
-                sync_committee_indices.push(candidate_index);
+        } else {
+            let active_validator_count = active_validator_indices.len();
+            let max_effective_balance =
+                spec.max_effective_balance_for_fork(self.fork_name_unchecked());
+            let max_random_value = if self.fork_name_unchecked().electra_enabled() {
+                MAX_RANDOM_VALUE
+            } else {
+                MAX_RANDOM_BYTE
+            };
+
+            let mut i = 0;
+            let mut sync_committee_indices = Vec::with_capacity(E::SyncCommitteeSize::to_usize());
+            while sync_committee_indices.len() < E::SyncCommitteeSize::to_usize() {
+                let shuffled_index = compute_shuffled_index(
+                    i.safe_rem(active_validator_count)?,
+                    active_validator_count,
+                    seed.as_slice(),
+                    spec.shuffle_round_count,
+                )
+                .ok_or(Error::UnableToShuffle)?;
+                let candidate_index = *active_validator_indices
+                    .get(shuffled_index)
+                    .ok_or(Error::ShuffleIndexOutOfBounds(shuffled_index))?;
+                let random_value = self.shuffling_random_value(i, seed.as_slice())?;
+                let effective_balance = self.get_validator(candidate_index)?.effective_balance;
+                if effective_balance.safe_mul(max_random_value)?
+                    >= max_effective_balance.safe_mul(random_value)?
+                {
+                    sync_committee_indices.push(candidate_index);
+                }
+                i.safe_add_assign(1)?;
             }
-            i.safe_add_assign(1)?;
+            Ok(sync_committee_indices)
         }
-        Ok(sync_committee_indices)
     }
 
     /// Compute the next sync committee.
@@ -2776,6 +2798,114 @@ impl<E: EthSpec> BeaconState<E> {
 
         Ok(())
     }
+
+    /// Get the PTC
+    /// Requires the committee cache to be initialized.
+    /// TODO(EIP-7732): definitely gonna have to cache this..
+    pub fn get_ptc(&self, slot: Slot, spec: &ChainSpec) -> Result<PTC<E>, Error> {
+        let committee_cache = self.committee_cache_at_slot(slot)?;
+        let committees = committee_cache.get_beacon_committees_at_slot(slot)?;
+
+        let seed = self.get_ptc_attester_seed(slot, spec)?;
+
+        let committee_indices: Vec<usize> = committees
+            .iter()
+            .flat_map(|committee| committee.committee.iter().copied())
+            .collect();
+        let selected_indices = self.compute_balance_weighted_selection(
+            &committee_indices,
+            &seed,
+            E::ptc_size(),
+            false,
+            spec,
+        )?;
+
+        Ok(PTC(FixedVector::new(selected_indices)?))
+    }
+
+    /// Compute the seed to use for the ptc attester selection at the given `slot`.
+    ///
+    /// Spec v0.12.1
+    pub fn get_ptc_attester_seed(&self, slot: Slot, spec: &ChainSpec) -> Result<Vec<u8>, Error> {
+        let epoch = slot.epoch(E::slots_per_epoch());
+        let mut preimage = self
+            .get_seed(epoch, Domain::PTCAttester, spec)?
+            .as_slice()
+            .to_vec();
+        preimage.append(&mut int_to_bytes8(slot.as_u64()));
+        Ok(hash(&preimage))
+    }
+
+    /// Return size indices sampled by effective balance, using indices as candidates.
+    ///
+    /// If shuffle_indices is True, candidate indices are themselves sampled from indices
+    /// by shuffling it, otherwise indices is traversed in order.
+    fn compute_balance_weighted_selection(
+        &self,
+        indices: &[usize],
+        seed: &[u8],
+        size: usize,
+        shuffle_indices: bool,
+        spec: &ChainSpec,
+    ) -> Result<Vec<usize>, Error> {
+        let total = indices.len();
+        if total == 0 {
+            return Err(Error::InvalidIndicesCount);
+        }
+
+        let mut selected = Vec::with_capacity(size);
+        let mut count = 0usize;
+
+        while selected.len() < size {
+            let mut next_index = count.safe_rem(total)?;
+
+            if shuffle_indices {
+                next_index =
+                    compute_shuffled_index(next_index, total, seed, spec.shuffle_round_count)
+                        .ok_or(Error::UnableToShuffle)?;
+            }
+
+            let candidate_index = indices.get(next_index).ok_or(Error::InvalidIndicesCount)?;
+
+            if self.compute_balance_weighted_acceptance(*candidate_index, seed, count, spec)? {
+                selected.push(*candidate_index);
+            }
+
+            count.safe_add_assign(1)?;
+        }
+
+        Ok(selected)
+    }
+
+    /// Return whether to accept the selection of the validator `index`, with probability
+    /// proportional to its `effective_balance`, and randomness given by `seed` and `iteration`.
+    fn compute_balance_weighted_acceptance(
+        &self,
+        index: usize,
+        seed: &[u8],
+        iteration: usize,
+        spec: &ChainSpec,
+    ) -> Result<bool, Error> {
+        // TODO(EIP-7732): Consider grabbing effective balances from the epoch cache here.
+        // Note that this function will be used in a loop, so using cached values could be nice for performance.
+        // However, post-gloas, this function will be used in `compute_proposer_indices`, `get_next_sync_committee_indices`, and `get_ptc`, which has ~15 call sites in total
+        // so we will need to check each one to ensure epoch cache is initialized first, if we deem a good idea.
+        // Currently, we can't test if making the change would work since the test suite is not ready for gloas.
+        let effective_balance = self.get_effective_balance(index)?;
+        let max_effective_balance = spec.max_effective_balance_for_fork(self.fork_name_unchecked());
+
+        let random_value = self.shuffling_random_value(iteration, seed)?;
+
+        // this codepath should technically never be hit pre-gloas, but added this defensively
+        let max_random_value = if self.fork_name_unchecked().electra_enabled() {
+            MAX_RANDOM_VALUE
+        } else {
+            MAX_RANDOM_BYTE
+        };
+
+        Ok(effective_balance.safe_mul(max_random_value)?
+            >= max_effective_balance.safe_mul(random_value)?)
+    }
 }
 
 impl<E: EthSpec> ForkVersionDecode for BeaconState<E> {

consensus/types/src/beacon_state/tests.rs

@@ -53,6 +53,16 @@ async fn build_state<E: EthSpec>(validator_count: usize) -> BeaconState<E> {
         .head_beacon_state_cloned()
 }
 
+/// TODO(EIP-7732): Add tests for PTC (Payload Timeliness Committee) functions:
+/// - get_ptc: Test committee selection, size, balance-weighted selection
+/// - get_ptc_attester_seed: Test seed generation and determinism
+/// - compute_balance_weighted_selection: Test selection algorithm with various balances
+/// - compute_balance_weighted_acceptance: Test acceptance probability
+/// These tests require being able to build Gloas states with initialized committee caches,
+/// which currently fails due to incomplete Gloas block structure as mentioned here:
+/// https://github.com/sigp/lighthouse/pull/8273
+/// Similar to existing committee_consistency_test suite for get_beacon_committee.
+
 async fn test_beacon_proposer_index<E: EthSpec>() {
     let spec = E::default_spec();
 

consensus/types/src/lib.rs

@@ -69,6 +69,7 @@ pub mod pending_deposit;
 pub mod pending_partial_withdrawal;
 pub mod proposer_preparation_data;
 pub mod proposer_slashing;
+pub mod ptc;
 pub mod relative_epoch;
 pub mod selection_proof;
 pub mod shuffling_id;
@@ -249,6 +250,7 @@ pub use crate::preset::{
 };
 pub use crate::proposer_preparation_data::ProposerPreparationData;
 pub use crate::proposer_slashing::ProposerSlashing;
+pub use crate::ptc::PTC;
 pub use crate::relative_epoch::{Error as RelativeEpochError, RelativeEpoch};
 pub use crate::runtime_fixed_vector::RuntimeFixedVector;
 pub use crate::runtime_var_list::RuntimeVariableList;

consensus/types/src/ptc.rs

@@ -0,0 +1,23 @@
+use crate::*;
+
+/// TODO(EIP-7732): is it easier to return u64 or usize?
+#[derive(Clone, Debug, PartialEq)]
+pub struct PTC<E: EthSpec>(pub FixedVector<usize, E::PTCSize>);
+
+impl<'a, E: EthSpec> IntoIterator for &'a PTC<E> {
+    type Item = &'a usize;
+    type IntoIter = std::slice::Iter<'a, usize>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.iter()
+    }
+}
+
+impl<E: EthSpec> IntoIterator for PTC<E> {
+    type Item = usize;
+    type IntoIter = std::vec::IntoIter<usize>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}