Merge remote-tracking branch 'origin/unstable' into tree-states

consensus/types/src/beacon_state.rs

@@ -141,6 +141,8 @@ pub enum Error {
     },
     TotalActiveBalanceDiffUninitialized,
     MissingImmutableValidator(usize),
+    IndexNotSupported(usize),
+    MerkleTreeError(merkle_proof::MerkleTreeError),
 }
 
 /// Control whether an epoch-indexed field can be indexed at the next epoch or not.
@@ -1660,6 +1662,60 @@ impl<T: EthSpec> BeaconState<T> {
         };
         Ok(sync_committee)
     }
+
+    pub fn compute_merkle_proof(
+        &mut self,
+        generalized_index: usize,
+    ) -> Result<Vec<Hash256>, Error> {
+        /* FIXME(sproul): re-enable merkle proofs
+        // 1. Convert generalized index to field index.
+        let field_index = match generalized_index {
+            light_client_update::CURRENT_SYNC_COMMITTEE_INDEX
+            | light_client_update::NEXT_SYNC_COMMITTEE_INDEX => {
+                // Sync committees are top-level fields, subtract off the generalized indices
+                // for the internal nodes. Result should be 22 or 23, the field offset of the committee
+                // in the `BeaconState`:
+                // https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/beacon-chain.md#beaconstate
+                generalized_index
+                    .checked_sub(tree_hash_cache::NUM_BEACON_STATE_HASH_TREE_ROOT_LEAVES)
+                    .ok_or(Error::IndexNotSupported(generalized_index))?
+            }
+            light_client_update::FINALIZED_ROOT_INDEX => {
+                // Finalized root is the right child of `finalized_checkpoint`, divide by two to get
+                // the generalized index of `state.finalized_checkpoint`.
+                let finalized_checkpoint_generalized_index = generalized_index / 2;
+                // Subtract off the internal nodes. Result should be 105/2 - 32 = 20 which matches
+                // position of `finalized_checkpoint` in `BeaconState`.
+                finalized_checkpoint_generalized_index
+                    .checked_sub(tree_hash_cache::NUM_BEACON_STATE_HASH_TREE_ROOT_LEAVES)
+                    .ok_or(Error::IndexNotSupported(generalized_index))?
+            }
+            _ => return Err(Error::IndexNotSupported(generalized_index)),
+        };
+
+        // 2. Get all `BeaconState` leaves.
+        let mut cache = self
+            .tree_hash_cache_mut()
+            .take()
+            .ok_or(Error::TreeHashCacheNotInitialized)?;
+        let leaves = cache.recalculate_tree_hash_leaves(self)?;
+        self.tree_hash_cache_mut().restore(cache);
+
+        // 3. Make deposit tree.
+        // Use the depth of the `BeaconState` fields (i.e. `log2(32) = 5`).
+        let depth = light_client_update::CURRENT_SYNC_COMMITTEE_PROOF_LEN;
+        let tree = merkle_proof::MerkleTree::create(&leaves, depth);
+        let (_, mut proof) = tree.generate_proof(field_index, depth)?;
+
+        // 4. If we're proving the finalized root, patch in the finalized epoch to complete the proof.
+        if generalized_index == light_client_update::FINALIZED_ROOT_INDEX {
+            proof.insert(0, self.finalized_checkpoint().epoch.tree_hash_root());
+        }
+
+        Ok(proof)
+        */
+        unimplemented!()
+    }
 }
 
 impl<T: EthSpec, V: ValidatorTrait> BeaconState<T, V> {
@@ -1718,6 +1774,12 @@ impl From<tree_hash::Error> for Error {
     }
 }
 
+impl From<merkle_proof::MerkleTreeError> for Error {
+    fn from(e: merkle_proof::MerkleTreeError) -> Error {
+        Error::MerkleTreeError(e)
+    }
+}
+
 impl From<ArithError> for Error {
     fn from(e: ArithError) -> Error {
         Error::ArithError(e)

consensus/types/src/chain_spec.rs

@@ -784,7 +784,7 @@ impl ChainSpec {
             domain_sync_committee_selection_proof: 8,
             domain_contribution_and_proof: 9,
             altair_fork_version: [0x01, 0x00, 0x00, 0x64],
-            altair_fork_epoch: Some(Epoch::new(256)),
+            altair_fork_epoch: Some(Epoch::new(512)),
 
             /*
              * Merge hard fork params
@@ -795,14 +795,11 @@ impl ChainSpec {
                 .expect("pow does not overflow"),
             proportional_slashing_multiplier_bellatrix: 3,
             bellatrix_fork_version: [0x02, 0x00, 0x00, 0x64],
-            bellatrix_fork_epoch: None,
-            terminal_total_difficulty: Uint256::MAX
-                .checked_sub(Uint256::from(2u64.pow(10)))
-                .expect("subtraction does not overflow")
-                // Add 1 since the spec declares `2**256 - 2**10` and we use
-                // `Uint256::MAX` which is `2*256- 1`.
-                .checked_add(Uint256::one())
-                .expect("addition does not overflow"),
+            bellatrix_fork_epoch: Some(Epoch::new(385536)),
+            terminal_total_difficulty: Uint256::from_dec_str(
+                "8626000000000000000000058750000000000000000000",
+            )
+            .expect("terminal_total_difficulty is a valid integer"),
             terminal_block_hash: ExecutionBlockHash::zero(),
             terminal_block_hash_activation_epoch: Epoch::new(u64::MAX),
             safe_slots_to_import_optimistically: 128u64,

consensus/types/src/config_and_preset.rs

@@ -40,7 +40,7 @@ impl ConfigAndPreset {
         let extra_fields = get_extra_fields(spec);
 
         if spec.bellatrix_fork_epoch.is_some()
-            || fork_name == None
+            || fork_name.is_none()
             || fork_name == Some(ForkName::Merge)
         {
             let bellatrix_preset = BellatrixPreset::from_chain_spec::<T>(spec);
@@ -65,7 +65,7 @@ impl ConfigAndPreset {
 
 /// Get a hashmap of constants to add to the `PresetAndConfig`
 pub fn get_extra_fields(spec: &ChainSpec) -> HashMap<String, Value> {
-    let hex_string = |value: &[u8]| format!("0x{}", hex::encode(&value)).into();
+    let hex_string = |value: &[u8]| format!("0x{}", hex::encode(value)).into();
     let u32_hex = |v: u32| hex_string(&v.to_le_bytes());
     let u8_hex = |v: u8| hex_string(&v.to_le_bytes());
     hashmap! {

consensus/types/src/deposit_tree_snapshot.rs

@@ -0,0 +1,83 @@
+use crate::*;
+use eth2_hashing::{hash32_concat, ZERO_HASHES};
+use int_to_bytes::int_to_bytes32;
+use serde_derive::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use test_random_derive::TestRandom;
+use test_utils::TestRandom;
+use DEPOSIT_TREE_DEPTH;
+
+#[derive(Encode, Decode, Deserialize, Serialize, Clone, Debug, PartialEq, TestRandom)]
+pub struct FinalizedExecutionBlock {
+    pub deposit_root: Hash256,
+    pub deposit_count: u64,
+    pub block_hash: Hash256,
+    pub block_height: u64,
+}
+
+impl From<&DepositTreeSnapshot> for FinalizedExecutionBlock {
+    fn from(snapshot: &DepositTreeSnapshot) -> Self {
+        Self {
+            deposit_root: snapshot.deposit_root,
+            deposit_count: snapshot.deposit_count,
+            block_hash: snapshot.execution_block_hash,
+            block_height: snapshot.execution_block_height,
+        }
+    }
+}
+
+#[derive(Encode, Decode, Deserialize, Serialize, Clone, Debug, PartialEq, TestRandom)]
+pub struct DepositTreeSnapshot {
+    pub finalized: Vec<Hash256>,
+    pub deposit_root: Hash256,
+    pub deposit_count: u64,
+    pub execution_block_hash: Hash256,
+    pub execution_block_height: u64,
+}
+
+impl Default for DepositTreeSnapshot {
+    fn default() -> Self {
+        let mut result = Self {
+            finalized: vec![],
+            deposit_root: Hash256::default(),
+            deposit_count: 0,
+            execution_block_hash: Hash256::zero(),
+            execution_block_height: 0,
+        };
+        // properly set the empty deposit root
+        result.deposit_root = result.calculate_root().unwrap();
+        result
+    }
+}
+
+impl DepositTreeSnapshot {
+    // Calculates the deposit tree root from the hashes in the snapshot
+    pub fn calculate_root(&self) -> Option<Hash256> {
+        let mut size = self.deposit_count;
+        let mut index = self.finalized.len();
+        let mut deposit_root = [0; 32];
+        for height in 0..DEPOSIT_TREE_DEPTH {
+            deposit_root = if (size & 1) == 1 {
+                index = index.checked_sub(1)?;
+                hash32_concat(self.finalized.get(index)?.as_bytes(), &deposit_root)
+            } else {
+                hash32_concat(&deposit_root, ZERO_HASHES.get(height)?)
+            };
+            size /= 2;
+        }
+        // add mix-in-length
+        deposit_root = hash32_concat(&deposit_root, &int_to_bytes32(self.deposit_count));
+
+        Some(Hash256::from_slice(&deposit_root))
+    }
+    pub fn is_valid(&self) -> bool {
+        self.calculate_root()
+            .map_or(false, |calculated| self.deposit_root == calculated)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    ssz_tests!(DepositTreeSnapshot);
+}

consensus/types/src/graffiti.rs

@@ -27,7 +27,7 @@ impl Graffiti {
 
 impl fmt::Display for Graffiti {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", eth2_serde_utils::hex::encode(&self.0))
+        write!(f, "{}", eth2_serde_utils::hex::encode(self.0))
     }
 }
 

consensus/types/src/lib.rs

@@ -36,6 +36,7 @@ pub mod contribution_and_proof;
 pub mod deposit;
 pub mod deposit_data;
 pub mod deposit_message;
+pub mod deposit_tree_snapshot;
 pub mod enr_fork_id;
 pub mod eth1_data;
 pub mod eth_spec;
@@ -49,6 +50,9 @@ pub mod free_attestation;
 pub mod graffiti;
 pub mod historical_batch;
 pub mod indexed_attestation;
+pub mod light_client_bootstrap;
+pub mod light_client_optimistic_update;
+pub mod light_client_update;
 pub mod pending_attestation;
 pub mod proposer_preparation_data;
 pub mod proposer_slashing;
@@ -116,6 +120,7 @@ pub use crate::contribution_and_proof::ContributionAndProof;
 pub use crate::deposit::{Deposit, DEPOSIT_TREE_DEPTH};
 pub use crate::deposit_data::DepositData;
 pub use crate::deposit_message::DepositMessage;
+pub use crate::deposit_tree_snapshot::{DepositTreeSnapshot, FinalizedExecutionBlock};
 pub use crate::enr_fork_id::EnrForkId;
 pub use crate::eth1_data::Eth1Data;
 pub use crate::eth_spec::EthSpecId;

consensus/types/src/light_client_bootstrap.rs

@@ -0,0 +1,44 @@
+use super::{BeaconBlockHeader, BeaconState, EthSpec, Hash256, SyncCommittee};
+use crate::{light_client_update::*, test_utils::TestRandom};
+use serde_derive::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use ssz_types::FixedVector;
+use std::sync::Arc;
+use test_random_derive::TestRandom;
+use tree_hash::TreeHash;
+
+/// A LightClientBootstrap is the initializer we send over to lightclient nodes
+/// that are trying to generate their basic storage when booting up.
+#[cfg_attr(feature = "arbitrary-fuzz", derive(arbitrary::Arbitrary))]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Encode, Decode, TestRandom)]
+#[serde(bound = "T: EthSpec")]
+pub struct LightClientBootstrap<T: EthSpec> {
+    /// Requested beacon block header.
+    pub header: BeaconBlockHeader,
+    /// The `SyncCommittee` used in the requested period.
+    pub current_sync_committee: Arc<SyncCommittee<T>>,
+    /// Merkle proof for sync committee
+    pub current_sync_committee_branch: FixedVector<Hash256, CurrentSyncCommitteeProofLen>,
+}
+
+impl<T: EthSpec> LightClientBootstrap<T> {
+    pub fn from_beacon_state(beacon_state: &mut BeaconState<T>) -> Result<Self, Error> {
+        let mut header = beacon_state.latest_block_header().clone();
+        header.state_root = beacon_state.tree_hash_root();
+        let current_sync_committee_branch =
+            beacon_state.compute_merkle_proof(CURRENT_SYNC_COMMITTEE_INDEX)?;
+        Ok(LightClientBootstrap {
+            header,
+            current_sync_committee: beacon_state.current_sync_committee()?.clone(),
+            current_sync_committee_branch: FixedVector::new(current_sync_committee_branch)?,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::MainnetEthSpec;
+
+    ssz_tests!(LightClientBootstrap<MainnetEthSpec>);
+}

consensus/types/src/light_client_finality_update.rs

@@ -0,0 +1,81 @@
+use super::{BeaconBlockHeader, EthSpec, FixedVector, Hash256, Slot, SyncAggregate, SyncCommittee};
+use crate::{light_client_update::*, test_utils::TestRandom, BeaconBlock, BeaconState, ChainSpec};
+use safe_arith::ArithError;
+use serde_derive::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use ssz_types::typenum::{U5, U6};
+use std::sync::Arc;
+use test_random_derive::TestRandom;
+use tree_hash::TreeHash;
+
+/// A LightClientFinalityUpdate is the update lightclient request or received by a gossip that
+/// signal a new finalized beacon block header for the light client sync protocol.
+#[cfg_attr(feature = "arbitrary-fuzz", derive(arbitrary::Arbitrary))]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Encode, Decode, TestRandom)]
+#[serde(bound = "T: EthSpec")]
+pub struct LightClientFinalityUpdate<T: EthSpec> {
+    /// The last `BeaconBlockHeader` from the last attested block by the sync committee.
+    pub attested_header: BeaconBlockHeader,
+    /// The last `BeaconBlockHeader` from the last attested finalized block (end of epoch).
+    pub finalized_header: BeaconBlockHeader,
+    /// Merkle proof attesting finalized header.
+    pub finality_branch: FixedVector<Hash256, FinalizedRootProofLen>,
+    /// current sync aggreggate
+    pub sync_aggregate: SyncAggregate<T>,
+    /// Slot of the sync aggregated singature
+    pub signature_slot: Slot,
+}
+
+impl<T: EthSpec> LightClientFinalityUpdate<T> {
+    pub fn new(
+        chain_spec: ChainSpec,
+        beacon_state: BeaconState<T>,
+        block: BeaconBlock<T>,
+        attested_state: &mut BeaconState<T>,
+        finalized_block: BeaconBlock<T>,
+    ) -> Result<Self, Error> {
+        let altair_fork_epoch = chain_spec
+            .altair_fork_epoch
+            .ok_or(Error::AltairForkNotActive)?;
+        if attested_state.slot().epoch(T::slots_per_epoch()) < altair_fork_epoch {
+            return Err(Error::AltairForkNotActive);
+        }
+
+        let sync_aggregate = block.body().sync_aggregate()?;
+        if sync_aggregate.num_set_bits() < chain_spec.min_sync_committee_participants as usize {
+            return Err(Error::NotEnoughSyncCommitteeParticipants);
+        }
+
+        // Compute and validate attested header.
+        let mut attested_header = attested_state.latest_block_header().clone();
+        attested_header.state_root = attested_state.tree_hash_root();
+        // Build finalized header from finalized block
+        let finalized_header = BeaconBlockHeader {
+            slot: finalized_block.slot(),
+            proposer_index: finalized_block.proposer_index(),
+            parent_root: finalized_block.parent_root(),
+            state_root: finalized_block.state_root(),
+            body_root: finalized_block.body_root(),
+        };
+        if finalized_header.tree_hash_root() != beacon_state.finalized_checkpoint().root {
+            return Err(Error::InvalidFinalizedBlock);
+        }
+
+        let finality_branch = attested_state.compute_merkle_proof(FINALIZED_ROOT_INDEX)?;
+        Ok(Self {
+            attested_header: attested_header,
+            finalized_header: finalized_header,
+            finality_branch: FixedVector::new(finality_branch)?,
+            sync_aggregate: sync_aggregate.clone(),
+            signature_slot: block.slot(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::MainnetEthSpec;
+
+    ssz_tests!(LightClientFinalityUpdate<MainnetEthSpec>);
+}

consensus/types/src/light_client_optimistic_update.rs

@@ -0,0 +1,59 @@
+use super::{BeaconBlockHeader, EthSpec, Slot, SyncAggregate};
+use crate::{
+    light_client_update::Error, test_utils::TestRandom, BeaconBlock, BeaconState, ChainSpec,
+};
+use serde_derive::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use test_random_derive::TestRandom;
+use tree_hash::TreeHash;
+
+/// A LightClientOptimisticUpdate is the update we send on each slot,
+/// it is based off the current unfinalized epoch is verified only against BLS signature.
+#[cfg_attr(feature = "arbitrary-fuzz", derive(arbitrary::Arbitrary))]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Encode, Decode, TestRandom)]
+#[serde(bound = "T: EthSpec")]
+pub struct LightClientOptimisticUpdate<T: EthSpec> {
+    /// The last `BeaconBlockHeader` from the last attested block by the sync committee.
+    pub attested_header: BeaconBlockHeader,
+    /// current sync aggreggate
+    pub sync_aggregate: SyncAggregate<T>,
+    /// Slot of the sync aggregated singature
+    pub signature_slot: Slot,
+}
+
+impl<T: EthSpec> LightClientOptimisticUpdate<T> {
+    pub fn new(
+        chain_spec: ChainSpec,
+        block: BeaconBlock<T>,
+        attested_state: BeaconState<T>,
+    ) -> Result<Self, Error> {
+        let altair_fork_epoch = chain_spec
+            .altair_fork_epoch
+            .ok_or(Error::AltairForkNotActive)?;
+        if attested_state.slot().epoch(T::slots_per_epoch()) < altair_fork_epoch {
+            return Err(Error::AltairForkNotActive);
+        }
+
+        let sync_aggregate = block.body().sync_aggregate()?;
+        if sync_aggregate.num_set_bits() < chain_spec.min_sync_committee_participants as usize {
+            return Err(Error::NotEnoughSyncCommitteeParticipants);
+        }
+
+        // Compute and validate attested header.
+        let mut attested_header = attested_state.latest_block_header().clone();
+        attested_header.state_root = attested_state.tree_hash_root();
+        Ok(Self {
+            attested_header,
+            sync_aggregate: sync_aggregate.clone(),
+            signature_slot: block.slot(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::MainnetEthSpec;
+
+    ssz_tests!(LightClientOptimisticUpdate<MainnetEthSpec>);
+}

consensus/types/src/light_client_update.rs

@@ -0,0 +1,173 @@
+use super::{BeaconBlockHeader, EthSpec, Hash256, Slot, SyncAggregate, SyncCommittee};
+use crate::{beacon_state, test_utils::TestRandom, BeaconBlock, BeaconState, ChainSpec};
+use safe_arith::ArithError;
+use serde_derive::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use ssz_types::{
+    typenum::{U5, U6},
+    FixedVector,
+};
+use std::sync::Arc;
+use test_random_derive::TestRandom;
+use tree_hash::TreeHash;
+
+pub const FINALIZED_ROOT_INDEX: usize = 105;
+pub const CURRENT_SYNC_COMMITTEE_INDEX: usize = 54;
+pub const NEXT_SYNC_COMMITTEE_INDEX: usize = 55;
+
+pub type FinalizedRootProofLen = U6;
+pub type CurrentSyncCommitteeProofLen = U5;
+pub type NextSyncCommitteeProofLen = U5;
+
+pub const FINALIZED_ROOT_PROOF_LEN: usize = 6;
+pub const CURRENT_SYNC_COMMITTEE_PROOF_LEN: usize = 5;
+pub const NEXT_SYNC_COMMITTEE_PROOF_LEN: usize = 5;
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum Error {
+    SszTypesError(ssz_types::Error),
+    BeaconStateError(beacon_state::Error),
+    ArithError(ArithError),
+    AltairForkNotActive,
+    NotEnoughSyncCommitteeParticipants,
+    MismatchingPeriods,
+    InvalidFinalizedBlock,
+}
+
+impl From<ssz_types::Error> for Error {
+    fn from(e: ssz_types::Error) -> Error {
+        Error::SszTypesError(e)
+    }
+}
+
+impl From<beacon_state::Error> for Error {
+    fn from(e: beacon_state::Error) -> Error {
+        Error::BeaconStateError(e)
+    }
+}
+
+impl From<ArithError> for Error {
+    fn from(e: ArithError) -> Error {
+        Error::ArithError(e)
+    }
+}
+
+/// A LightClientUpdate is the update we request solely to either complete the bootstraping process,
+/// or to sync up to the last committee period, we need to have one ready for each ALTAIR period
+/// we go over, note: there is no need to keep all of the updates from [ALTAIR_PERIOD, CURRENT_PERIOD].
+#[cfg_attr(feature = "arbitrary-fuzz", derive(arbitrary::Arbitrary))]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Encode, Decode, TestRandom)]
+#[serde(bound = "T: EthSpec")]
+pub struct LightClientUpdate<T: EthSpec> {
+    /// The last `BeaconBlockHeader` from the last attested block by the sync committee.
+    pub attested_header: BeaconBlockHeader,
+    /// The `SyncCommittee` used in the next period.
+    pub next_sync_committee: Arc<SyncCommittee<T>>,
+    /// Merkle proof for next sync committee
+    pub next_sync_committee_branch: FixedVector<Hash256, NextSyncCommitteeProofLen>,
+    /// The last `BeaconBlockHeader` from the last attested finalized block (end of epoch).
+    pub finalized_header: BeaconBlockHeader,
+    /// Merkle proof attesting finalized header.
+    pub finality_branch: FixedVector<Hash256, FinalizedRootProofLen>,
+    /// current sync aggreggate
+    pub sync_aggregate: SyncAggregate<T>,
+    /// Slot of the sync aggregated singature
+    pub signature_slot: Slot,
+}
+
+impl<T: EthSpec> LightClientUpdate<T> {
+    pub fn new(
+        chain_spec: ChainSpec,
+        beacon_state: BeaconState<T>,
+        block: BeaconBlock<T>,
+        attested_state: &mut BeaconState<T>,
+        finalized_block: BeaconBlock<T>,
+    ) -> Result<Self, Error> {
+        let altair_fork_epoch = chain_spec
+            .altair_fork_epoch
+            .ok_or(Error::AltairForkNotActive)?;
+        if attested_state.slot().epoch(T::slots_per_epoch()) < altair_fork_epoch {
+            return Err(Error::AltairForkNotActive);
+        }
+
+        let sync_aggregate = block.body().sync_aggregate()?;
+        if sync_aggregate.num_set_bits() < chain_spec.min_sync_committee_participants as usize {
+            return Err(Error::NotEnoughSyncCommitteeParticipants);
+        }
+
+        let signature_period = block.epoch().sync_committee_period(&chain_spec)?;
+        // Compute and validate attested header.
+        let mut attested_header = attested_state.latest_block_header().clone();
+        attested_header.state_root = attested_state.tree_hash_root();
+        let attested_period = attested_header
+            .slot
+            .epoch(T::slots_per_epoch())
+            .sync_committee_period(&chain_spec)?;
+        if attested_period != signature_period {
+            return Err(Error::MismatchingPeriods);
+        }
+        // Build finalized header from finalized block
+        let finalized_header = BeaconBlockHeader {
+            slot: finalized_block.slot(),
+            proposer_index: finalized_block.proposer_index(),
+            parent_root: finalized_block.parent_root(),
+            state_root: finalized_block.state_root(),
+            body_root: finalized_block.body_root(),
+        };
+        if finalized_header.tree_hash_root() != beacon_state.finalized_checkpoint().root {
+            return Err(Error::InvalidFinalizedBlock);
+        }
+        let next_sync_committee_branch =
+            attested_state.compute_merkle_proof(NEXT_SYNC_COMMITTEE_INDEX)?;
+        let finality_branch = attested_state.compute_merkle_proof(FINALIZED_ROOT_INDEX)?;
+        Ok(Self {
+            attested_header,
+            next_sync_committee: attested_state.next_sync_committee()?.clone(),
+            next_sync_committee_branch: FixedVector::new(next_sync_committee_branch)?,
+            finalized_header,
+            finality_branch: FixedVector::new(finality_branch)?,
+            sync_aggregate: sync_aggregate.clone(),
+            signature_slot: block.slot(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::MainnetEthSpec;
+    use ssz_types::typenum::Unsigned;
+
+    ssz_tests!(LightClientUpdate<MainnetEthSpec>);
+
+    #[test]
+    fn finalized_root_params() {
+        assert!(2usize.pow(FINALIZED_ROOT_PROOF_LEN as u32) <= FINALIZED_ROOT_INDEX);
+        assert!(2usize.pow(FINALIZED_ROOT_PROOF_LEN as u32 + 1) > FINALIZED_ROOT_INDEX);
+        assert_eq!(FinalizedRootProofLen::to_usize(), FINALIZED_ROOT_PROOF_LEN);
+    }
+
+    #[test]
+    fn current_sync_committee_params() {
+        assert!(
+            2usize.pow(CURRENT_SYNC_COMMITTEE_PROOF_LEN as u32) <= CURRENT_SYNC_COMMITTEE_INDEX
+        );
+        assert!(
+            2usize.pow(CURRENT_SYNC_COMMITTEE_PROOF_LEN as u32 + 1) > CURRENT_SYNC_COMMITTEE_INDEX
+        );
+        assert_eq!(
+            CurrentSyncCommitteeProofLen::to_usize(),
+            CURRENT_SYNC_COMMITTEE_PROOF_LEN
+        );
+    }
+
+    #[test]
+    fn next_sync_committee_params() {
+        assert!(2usize.pow(NEXT_SYNC_COMMITTEE_PROOF_LEN as u32) <= NEXT_SYNC_COMMITTEE_INDEX);
+        assert!(2usize.pow(NEXT_SYNC_COMMITTEE_PROOF_LEN as u32 + 1) > NEXT_SYNC_COMMITTEE_INDEX);
+        assert_eq!(
+            NextSyncCommitteeProofLen::to_usize(),
+            NEXT_SYNC_COMMITTEE_PROOF_LEN
+        );
+    }
+}