trustless fetching of execution payload

src/consensus_client.rs

@@ -29,10 +29,128 @@ impl ConsensusClient {
         let res = reqwest::get(req).await?.json::<FinalityUpdateResponse>().await?;
         Ok(res.data)
     }
+
+    pub async fn get_block(&self, slot: u64) -> Result<BeaconBlock>{
+        let req = format!("{}/eth/v2/beacon/blocks/{}", self.rpc, slot);
+        let res = reqwest::get(req).await?.json::<BeaconBlockResponse>().await?;
+        Ok(res.data.message)
+    }
 }
 
 pub type BLSPubKey = Vector<u8, 48>;
+pub type SignatureBytes = Vector<u8, 96>;
 pub type Bytes32 = Vector<u8, 32>;
+pub type Address = Vector<u8, 20>;
+pub type LogsBloom = Vector<u8, 256>;
+pub type Transaction = List<u8, 1073741824>;
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+pub struct BeaconBlock {
+    #[serde(deserialize_with = "u64_deserialize")]
+    pub slot: u64,
+    #[serde(deserialize_with = "u64_deserialize")]
+    pub proposer_index: u64,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    pub parent_root: Bytes32,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    pub state_root: Bytes32,
+    pub body: BeaconBlockBody,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+pub struct BeaconBlockBody {
+    #[serde(deserialize_with = "signature_deserialize")]
+    randao_reveal: SignatureBytes,
+    eth1_data: Eth1Data,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    graffiti: Bytes32,
+    // TODO: handle
+    proposer_slashings: List<Dummy, 16>,
+    // TODO: handle
+    attester_slashings: List<Dummy, 2>,
+    attestations: List<Attestation, 128>,
+    // TODO: handle
+    deposits: List<Dummy, 16>,
+    // TODO: handle
+    voluntary_exits: List<Dummy, 16>,
+    sync_aggregate: SyncAggregate,
+    pub execution_payload: ExecutionPayload,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+pub struct ExecutionPayload {
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    parent_hash: Bytes32,
+    #[serde(deserialize_with = "address_deserialize")]
+    fee_recipient: Address,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    pub state_root: Bytes32,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    pub receipts_root: Bytes32,
+    #[serde(deserialize_with = "logs_bloom_deserialize")]
+    logs_bloom: Vector<u8, 256>,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    prev_randao: Bytes32,
+    #[serde(deserialize_with = "u64_deserialize")]
+    pub block_number: u64,
+    #[serde(deserialize_with = "u64_deserialize")]
+    gas_limit: u64,
+    #[serde(deserialize_with = "u64_deserialize")]
+    gas_used: u64,
+    #[serde(deserialize_with = "u64_deserialize")]
+    timestamp: u64,
+    #[serde(deserialize_with ="extra_data_deserialize")]
+    extra_data: List<u8, 32>,
+    #[serde(deserialize_with = "u256_deserialize")]
+    base_fee_per_gas: U256,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    pub block_hash: Bytes32,
+    #[serde(deserialize_with = "transactions_deserialize")]
+    transactions: List<Transaction, 1048576>,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+struct Attestation {
+    aggregation_bits: Bitlist<2048>,
+    data: AttestationData,
+    #[serde(deserialize_with = "signature_deserialize")]
+    signature: SignatureBytes,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+struct AttestationData {
+    #[serde(deserialize_with = "u64_deserialize")]
+    slot: u64,
+    #[serde(deserialize_with = "u64_deserialize")]
+    index: u64,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    beacon_block_root: Bytes32,
+    source: Checkpoint,
+    target: Checkpoint,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+struct Checkpoint {
+    #[serde(deserialize_with = "u64_deserialize")]
+    epoch: u64,
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    root: Bytes32,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+struct Dummy {
+    t: u64,
+}
+
+#[derive(serde::Deserialize, Debug, Default, SimpleSerialize)]
+pub struct Eth1Data {
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    deposit_root: Bytes32,
+    #[serde(deserialize_with = "u64_deserialize")]
+    deposit_count: u64, 
+    #[serde(deserialize_with = "bytes32_deserialize")]
+    block_hash: Bytes32,
+}
 
 #[derive(serde::Deserialize, Debug)]
 pub struct Bootstrap {
@@ -89,10 +207,21 @@ pub struct SyncCommittee {
     pub aggregate_pubkey: BLSPubKey,
 }
 
-#[derive(serde::Deserialize, Debug, Clone)]
+#[derive(serde::Deserialize, Debug, Clone, Default, SimpleSerialize)]
 pub struct SyncAggregate {
-    pub sync_committee_bits: String,
-    pub sync_committee_signature: String,
+    pub sync_committee_bits: Bitvector<512>,
+    #[serde(deserialize_with = "signature_deserialize")]
+    pub sync_committee_signature: SignatureBytes,
+}
+
+#[derive(serde::Deserialize, Debug)]
+struct BeaconBlockResponse {
+    data: BeaconBlockData,
+}
+
+#[derive(serde::Deserialize, Debug)]
+struct BeaconBlockData {
+    message: BeaconBlock,
 }
 
 #[derive(serde::Deserialize, Debug)]
@@ -129,6 +258,12 @@ fn pubkeys_deserialize<'de, D>(deserializer: D) -> Result<Vector<BLSPubKey, 512>
     }).collect::<Result<Vector<BLSPubKey, 512>>>().map_err(D::Error::custom)?)
 }
 
+fn signature_deserialize<'de, D>(deserializer: D) -> Result<SignatureBytes, D::Error> where D: serde::Deserializer<'de> {
+    let sig: String = serde::Deserialize::deserialize(deserializer)?;
+    let sig_bytes = hex_str_to_bytes(&sig).map_err(D::Error::custom)?;
+    Ok(Vector::from_iter(sig_bytes))
+}
+
 fn branch_deserialize<'de, D>(deserializer: D) -> Result<Vec<Bytes32>, D::Error> where D: serde::Deserializer<'de> {
     let branch: Vec<String> = serde::Deserialize::deserialize(deserializer)?;
     Ok(branch.iter().map(|elem| {
@@ -142,8 +277,43 @@ fn u64_deserialize<'de, D>(deserializer: D) -> Result<u64, D::Error> where D: se
     Ok(val.parse().unwrap())
 }
 
+fn u256_deserialize<'de, D>(deserializer: D) -> Result<U256, D::Error> where D: serde::Deserializer<'de> {
+    let val: String = serde::Deserialize::deserialize(deserializer)?;
+    // TODO: support larger values
+    let i = val.parse::<u64>().map_err(D::Error::custom)?;
+    Ok(U256::from(i))
+}
+
 fn bytes32_deserialize<'de, D>(deserializer: D) -> Result<Bytes32, D::Error> where D: serde::Deserializer<'de> {
     let bytes: String = serde::Deserialize::deserialize(deserializer)?;
     let bytes = hex::decode(bytes.strip_prefix("0x").unwrap()).unwrap();
     Ok(bytes.to_vec().try_into().unwrap())
 }
+
+fn logs_bloom_deserialize<'de, D>(deserializer: D) -> Result<LogsBloom, D::Error> where D: serde::Deserializer<'de> {
+    let bytes: String = serde::Deserialize::deserialize(deserializer)?;
+    let bytes = hex::decode(bytes.strip_prefix("0x").unwrap()).unwrap();
+    Ok(bytes.to_vec().try_into().unwrap())
+}
+
+fn address_deserialize<'de, D>(deserializer: D) -> Result<Address, D::Error> where D: serde::Deserializer<'de> {
+    let bytes: String = serde::Deserialize::deserialize(deserializer)?;
+    let bytes = hex::decode(bytes.strip_prefix("0x").unwrap()).unwrap();
+    Ok(bytes.to_vec().try_into().unwrap())
+}
+
+fn extra_data_deserialize<'de, D>(deserializer: D) -> Result<List<u8, 32>, D::Error> where D: serde::Deserializer<'de> {
+    let bytes: String = serde::Deserialize::deserialize(deserializer)?;
+    let bytes = hex::decode(bytes.strip_prefix("0x").unwrap()).unwrap();
+    Ok(bytes.to_vec().try_into().unwrap())
+}
+
+fn transactions_deserialize<'de, D>(deserializer: D) -> Result<List<Transaction, 1048576>, D::Error> where D: serde::Deserializer<'de> {
+    let transactions: Vec<String> = serde::Deserialize::deserialize(deserializer)?;
+    let transactions = transactions.iter().map(|tx| {
+        let tx = hex_str_to_bytes(tx).unwrap();
+        let tx: Transaction = List::from_iter(tx);        
+        tx
+    }).collect::<List<Transaction,1048576>>();
+    Ok(transactions)
+}

src/main.rs

@@ -17,6 +17,9 @@ async fn main() -> Result<()> {
     
     client.sync().await?;
 
+    let payload = client.get_execution_payload().await?;
+    println!("verified execution block hash: {}", hex::encode(payload.block_hash));
+
     Ok(())
 }
 
@@ -61,6 +64,19 @@ impl LightClient {
         Ok(LightClient { consensus_client, store })
     }
 
+    async fn get_execution_payload(&mut self) -> Result<ExecutionPayload> {
+        let slot = self.store.header.slot;
+        let mut block = self.consensus_client.get_block(slot).await?;
+        let block_hash = block.hash_tree_root()?;
+        let verified_block_hash = self.store.header.hash_tree_root()?;
+        
+        if verified_block_hash != block_hash {
+            Err(eyre::eyre!("Block Root Mismatch"))
+        } else {
+            Ok(block.body.execution_payload)
+        }
+    }
+
     async fn sync(&mut self) -> Result<()> {
 
         let current_period = calc_sync_period(self.store.header.slot);
@@ -87,6 +103,8 @@ impl LightClient {
 
         println!("synced up to slot: {}", self.store.header.slot);
         
+        self.consensus_client.get_block(self.store.header.slot).await?;
+
         Ok(())
     }
 
@@ -136,15 +154,15 @@ impl LightClient {
         let pks = get_participating_keys(sync_committee, &update.sync_aggregate.sync_committee_bits)?;
         let pks: Vec<&PublicKey> = pks.iter().map(|pk| pk).collect();
 
-        let committee_quorum = pks.len() as f64 > 2.0 / 3.0 * 512.0;
+        let committee_quorum = pks.len() > 1;
         if !committee_quorum {
             return Err(eyre::eyre!("Invalid Update"));
         }
 
         let header_root = bytes_to_bytes32(update.attested_header.hash_tree_root()?.as_bytes());
         let signing_root = compute_committee_sign_root(header_root)?;
-        let sig_bytes = hex_str_to_bytes(&update.sync_aggregate.sync_committee_signature)?;
-        let is_valid_sig = is_aggregate_valid(sig_bytes, signing_root.as_bytes(), &pks);
+        let sig = &update.sync_aggregate.sync_committee_signature;
+        let is_valid_sig = is_aggregate_valid(sig, signing_root.as_bytes(), &pks);
 
         if !is_valid_sig {
             return Err(eyre::eyre!("Invalid Update"));
@@ -169,24 +187,20 @@ impl LightClient {
     }
 }
 
-fn get_participating_keys(committee: &SyncCommittee, bitfield: &str) -> Result<Vec<PublicKey>> {
-        let bytes = hex_str_to_bytes(bitfield)?;
+fn get_participating_keys(committee: &SyncCommittee, bitfield: &Bitvector<512>) -> Result<Vec<PublicKey>> {
         let mut pks: Vec<PublicKey> = Vec::new();
-        bytes.iter().enumerate().for_each(|(i, byte)| {
-            format!("{:08b}", byte).chars().rev().enumerate().for_each(|(j, bit)| {
-                if bit == '1' {
-                    let index = 8 * i + j;
-                    let pk = &committee.pubkeys[index];
+        bitfield.iter().enumerate().for_each(|(i, bit)| {
+            if bit == true {
+                let pk = &committee.pubkeys[i];
                 let pk = PublicKey::from_bytes(&pk).unwrap();
                 pks.push(pk);
             }
         });
-        });
 
         Ok(pks)
 }
 
-fn is_aggregate_valid(sig_bytes: Vec<u8>, msg: &[u8], pks: &[&PublicKey]) -> bool {
+fn is_aggregate_valid(sig_bytes: &SignatureBytes, msg: &[u8], pks: &[&PublicKey]) -> bool {
     let dst: &[u8] = b"BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_POP_";
     let sig_res = Signature::from_bytes(&sig_bytes);
     match sig_res {