AIP: BoLD - permissionless validation for Arbitrum

This Snapshot vote aims to solicit a temperature check from the ArbitrumDAO on their stance for bringing the BoLD upgrade to Arbitrum One and Nova. BoLD is a new dispute resolution protocol that unlocks permissionless validation for Arbitrum chains and enhances their security by mitigating the risk of delay attacks.

For more information, please refer to the original BoLD AIP Forum Post where you will find public audit reports, the BoLD whitepaper (that contain the formal specification and safety proofs), as well as further explanations of how BoLD works (including an overview of BoLD’s economics, spam prevention, rewards, reimbursements and penalties) and its proposed design for Arbitrum One and Arbitrum Nova.

Constitutional Proposal

Abstract

This Constitutional AIP proposes upgrading Arbitrum One and Arbitrum Nova’s Rollup Contracts to use Arbitrum BoLD and to support a new challenger manager contract on Ethereum. Arbitrum BoLD is a new dispute resolution protocol that’s designed to replace the existing and currently deployed Arbitrum protocol. If the upgrade is approved, then validators on Arbitrum One and Arbitrum Nova can use the Nitro software to participate in BoLD. BoLD delivers two critical improvements:

• Unlocks permissionless validation for Arbitrum chains,
• Enhances the security of Arbitrum chains by mitigating the risk of delay attacks.

BoLD accomplishes this feat by ensuring that any single honest party can always successfully defend against malicious claims to an Arbitrum chain’s state. BoLD represents the next step on the journey to having the Arbitrum technology stack being recognized as a Stage 2 Ethereum rollup. The implementation of BoLD will be thoroughly tested to ensure both its effectiveness and safety. The testing plan includes:

• A comprehensive audit by Trail of Bits,
• Deployment of the protocol to public testnets for at least 8 weeks,
• A public audit program,
• Publication of mathematical safety proofs and formal specifications.

Motivation

The ArbitrumDAO should consider approving this AIP as BoLD delivers critical security and decentralization improvements for Arbitrum One and Nova that benefit all Arbitrum users, Arbitrum node operators, dApps on Arbitrum, and Arbitrum bridges. These benefits can be extended to any Orbit chain that wishes to adopt BoLD.

More specifically, this new dispute resolution protocol brings the following benefits to Arbitrum chains:

• Permissionless validation
• Fixed delay time for assertion confirmation
• Security Council Safety-First Approach

More details on these benefits can be found in the Motivation section of the original proposal.

Rationale

Enabling permissionless validation has been a long-term goal of Arbitrum on the progressive journey towards decentralization.

BoLD mitigates the risk of delay attacks on Optimistic Rollups by ensuring challenges can be resolved within a fixed time period as long as there is an honest party involved. This particular change unlocks permissionless validation, enabling any well-resourced honest party or parties to defend and protect Arbitrum from malicious actors.

More details on the community values that this proposal supports, can be found in the Rationale section of the original proposal.

Implementation, Formal Specification, and Safety Proofs

The following link, BoLD Implementation Deep Dive, explains how BoLD is implemented and how it works at a high level. To read about the formal specifications and mathematical safety proofs for the protocol, check out the official BoLD whitepaper.

Economics of Disputes, including the cost to participate, rewards, and penalties

The economics behind BoLD are carefully researched and designed to optimize for the security of the protocol while keeping costs reasonable for honest parties. More details on this topic can be found in the Economics section of the original proposal and this short paper on the Economics of Disputes in BoLD.

Technical Risks

Some of the technical risks of the BoLD upgrade include:

• Issues preventing liveness of challenges due to smart contract bugs in the new contracts. For instance, no honest validator able to make a move when it should be able to;
• Safety issues where a malicious party is able to game the system and win due to logic errors in smart contracts;
• Logic bugs in the assertion smart contracts that could affect assertion confirmation and posting, which could delay withdrawals until it is fixed; and
• Bugs in bonding logic in the smart contracts that could lead to loss of funds due to logic errors in the Arbitrum Rollup and challenge manager smart contracts.

Risks that remain the same between the current Arbitrum Rollup protocol and BoLD:

• Bugs in the one step proof logic: BoLD does not change how one step proofs work for Arbitrum chains.

Timeline and steps to implement BoLD for Arbitrum One and Nova

Below is a list of initiatives to ensure the new BoLD dispute resolution protocol is ready to be reviewed and voted on by the ArbitrumDAO for adoption in Arbitrum One and Nova. Feedback from the community and any findings from testing will be collected and used to inform decisions and evolve BoLD along the way.

1. Deployment of a public testnet with BoLD validators for a minimum of 4 weeks a. Check out this guide on how to deploy a BoLD validator on the testnet to begin testing out permissionless validation using Arbitrum technology!
2. The submission of the AIP in the format of a forum post.
3. Audit of the protocol’s implementation by Trail of Bits
4. Hosting of governance calls to talk about BoLD to answer questions from the community about BoLD and this AIP.
5. This formal temperature check proposal to activate BoLD on Arbitrum’s Sepolia for a minimum of 4 weeks, be made via a Snapshot vote.
6. Kick-start a public audit program.
7. Finalize pre-mainnet requirements, including: a. Publication of BoLD migration documentation for existing validators; b. Deployment of a monitoring stack to view on-going challenges on an Arbitrum chain; and c. Publication of a formal procedure for The Arbitrum Foundation to handle L1 gas costs reimbursements for honest parties.
8. Formal AIP gets submitted to Tally.
9. Should the formal on-chain proposal pass, BoLD will activate on Arbitrum One and Nova.

Overall Cost

There is no cost for this proposal to the ArbitrumDAO as Offchain Labs, Inc. will incur all engineering and audit costs to complete the implementation of BoLD and get this new dispute resolution protocol into a mainnet-ready state. Currently, future development work for BoLD is expected to also be undertaken by Offchain Labs, Inc.

Disclaimer

The confirmation timing on any withdrawal that is in-flight when the proposed BoLD upgrade is activated will be delayed until the first BoLD assertion is confirmed. This means that for any Arbitrum chain that upgrades to use BoLD, including Arbitrum One and Arbitrum Nova, all pending withdrawals to L1 Ethereum that were initiated before the upgrade will be delayed by 1 challenge period, plus the time between the withdrawal was initiated and the time that the BoLD upgrade takes place. This is because the upgrade effectively “resets” the challenge period for that are not yet finalized.

FAQ

For additional topics & questions, please visit the BoLD specific FAQ document here.