Tsvetan Dimitrov

Agenda

• Problem

• General Solution

• Requirements

• Cross-Chain Messaging Protocol Overview

Problem

• Dispersion of users across rollups.

• Complicated management of several subcomponents across independent rollups to access all of Ethereum’s users and capital.

General Solution

• Ethereum requires a native interoperability protocol purpose-built to realign with its original vision of being a single unified operating system for dapps.

Requirements / 1

• Verification of the state of a source network and relaying state updates to destination networks.

• Derive security from the source that rollups derive it from - Ethereum L1.

• Minimal latency to verify and process cross-rollup messages.

Requirements / 2

• Global compatibility - it must enable applications to be Turing-complete across all rollup envs, ensuring that applications are not limited by the resource constraints of any single rollup

Cross-Chain Messaging Protocol

Condition: Source Chain Gas Fees should be paid.

Condition: Source Chain Block should be finalized.

XStreamOffset

XStream

1. Halo constructs XBlocks from XMsgs

XBlock

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XMsgs are partitioned for inclusion into subranges by the Relayer , verified by Merkle Multiproofs to optimize for submission gas costs.

ABCI++

Quorum votes constitute an approved attestation.

Validators vote for XBlocks.

PrepareProposal

ProcessProposal

ExtendVote

VerifyVoteExtensions

FinalizeBlock

Voting

• Validators return an array of Votes during the ABCI++ ExtendVote method.

• Validators should reject vote extensions that contain invalid votes via VerifyVoteExtension.

• Proposers aggregate votes from the previous block with those from the current one.

• Quorum votes (66% of validators in the set) constitute an approved Attestation.

• Validators in the current validator set must vote for all subsequent Attestations.

Why votes from the previous block are included together with votes from the current block?

• Proof that the previous block has reached consensus.

• Identifying forks in the chain, ensuring validators only extend the chain from the correct version.

• Finalize the state changes from the previous block by applying them before starting the process for the current block.

• Supports deterministic block proposals based on all the valid information available.

Validator Set Change

• All pending Attestations need to be updated with:

  • The current validator set ID.

  • Removing all attestations by validators not in the current set.

  • Updating the weights (cumulative validator voting power) of each remaining attestation according to the new validator set.

• Only new validators need to re-attest.

Halo

Relayer collects finalized XBlock and signatures

Relayer monitors for approved Attestations

Relayer submits Submissions to destination rollup

Summary

• Define Problem and System Solution.

• Define requirements and properties the system must adhere to.

• Present components and flow of the Cross-Chain Messaging Protocol.

Questions?