nimbus-eth2/beacon_chain/gossip_processing/README.md

Gossip Processing

This folder holds a collection of modules to:

• validate raw gossip data before
  • rebroadcasting it (potentially aggregated)
  • sending it to one of the consensus object pools

Validation

Gossip validation is different from consensus verification in particular for blocks.

• Blocks: https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/phase0/p2p-interface.md#beacon_block
• Attestations (aggregated): https://github.com/ethereum/consensus-specs/blob/v1.0.1/specs/phase0/p2p-interface.md#beacon_aggregate_and_proof
• Attestations (unaggregated): https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/phase0/p2p-interface.md#attestation-subnets
• Voluntary exits: https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/phase0/p2p-interface.md#voluntary_exit
• Proposer slashings: https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/phase0/p2p-interface.md#proposer_slashing
• Attester slashing: https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/phase0/p2p-interface.md#attester_slashing

There are multiple consumers of validated consensus objects:

• a ValidationResult.Accept output triggers rebroadcasting in libp2p
  • We jump into method validate(PubSub, Message) in libp2p/protocols/pubsub/pubsub.nim
  • which was called by rpcHandler(GossipSub, PubSubPeer, RPCMsg)
• a blockValidator message enqueues the validated object to the processing queue in block_processor
  • blocksQueue: AsyncQueue[BlockEntry] (shared with request_manager and sync_manager)
  • This queue is then regularly processed to be made available to the consensus object pools.
• a xyzValidator message adds the validated object to a pool in eth2_processor
  • Attestations (unaggregated and aggregated) get collected into batches.
  • Once a threshold is exceeded or after a timeout, they get validated together using BatchCrypto.

Security concerns

As the first line of defense in Nimbus, modules must be able to handle bursts of data that may come:

• from malicious nodes trying to DOS us
• from long periods of non-finality, creating lots of forks, attestations