Arbitrum BOLD Testnet Live: The Next Step in Decentralization

Written by Raul Jordan, Derek Lee, David Dennis

Offchain Labs is thrilled to announce another milestone in the evolution of Arbitrum: the testnet availability of Arbitrum BOLD — the next-generation dispute resolution protocol with working, interactive fraud proofs for optimistic rollups. Building upon the foundation laid in our original announcement of BOLD on August 3, 2023, this announcement marks another step towards fully permissionless validation on Arbitrum chains and greater decentralization.

Fraud proofs on rollups are only as useful as the dispute process that runs them. Arbitrum has been secured using fraud proofs in production from day-one, and the Offchain Labs team has continued to iterate on creating a dispute resolution protocol for Arbitrum that is permissionless, safe, and solves many of the pitfalls other designs suffer from. BOLD guarantees a fixed upper-bound on the confirmation of Arbitrum states on Ethereum and allows a single, well-resourced party to defend claims against many adversaries without needing to play 1-vs-1 games against them.

Arbitrum has always been committed to scalability, efficiency, and security. As part of Offchain Labs’ comprehensive plan to ensure BOLD is rigorously tested and robust in design, we’ve deployed the implementation of BOLD on a public testnet. The BOLD-enabled public testnet validates and posts assertions to Ethereum Sepolia and gives the community a chance to deploy a BOLD validator to see this bleeding-edge dispute protocol in action. Shortly after, we expect a proposal will be made to activate BOLD on Arbitrum Sepolia, followed by a Tally vote.

Why is permissionless validation important for decentralization & Arbitrum?

So, what exactly does permissionless validation mean for Arbitrum? In essence, it empowers anyone to secure claims made about Arbitrum’s state on Ethereum. That is, withdrawals from Arbitrum back to Ethereum can be verified or challenged by anyone in the world, ensuring the correct history always remains correct. Currently, Arbitrum validators are allow-listed, but with BOLD, the use of a permissioned list of validators will no longer be necessary. This democratization of validation will not only enhance the security and resilience of the network, but also foster greater decentralization and resiliency within the ecosystem.

BOLD’s benefits for the Arbitrum community include:

• Permissionless Validation: Participants can run their own validator nodes and contribute to the consensus process, helping to secure the network and validate withdrawals back to Ethereum.
• Enhanced Security: BOLD taps into the 10 years of experience the Offchain Labs team has in designing interactive proving protocols to create a new system for Arbitrum that is resilient to delay attacks and allows a single, well-resourced honest party to defeat many evil parties without needing to play 1-vs-1 games. Honest BOLD validators will win against evil claims within a fixed upper-bound of 7 days and have their stakes reimbursed when disputes are resolved, so long as they follow the protocol.
• Pooled Challenge Funding: Issuing a challenge requires significant funding. However, anyone can create a trustless smart contract to pool funds together and defend Arbitrum against invalid claims, or challenge invalid claims posted by others.
• Mathematical Foundations: After over a year in development, the Offchain Labs research team has produced formal safety proofs for BOLD. The BOLD smart contracts are currently being thoroughly audited by Trail of Bits.

Getting Closer to Stage Two

In his recent blog, “Ethereum has blobs. Where do we go from here?” Vitalik writes about many aspects of improving Ethereum L2s, including the need for continuous improvements to security and decentralization.

BOLD has the potential to take another major step for Arbitrum along this journey by addressing the (currently yellow) State Validation wedge in the L2 Beat risk analysis pie chart. L2 Beat’s commentary currently notes:

Fraud proofs allow 14 WHITELISTED actors watching the chain to prove that the state is incorrect.

By replacing the allowlisted validators with permissionless validators via BOLD, Arbitrum chains will be able to address this particular concern and move further towards greater decentralization and achieve even greater Ethereum alignment.

This sounds cool! How do I learn more?

The launch of BOLD on a public testnet is the first step of many on the roadmap to bring BOLD to mainnet readiness and, eventually, to Arbitrum One and Nova via a DAO vote. Below are a few great resources to learn more about BOLD and stay up-to-date with product updates!

• Read the BOLD Gentle Introduction docs for a primer on how BOLD works and why we built it for Arbitrum!
• To view BOLD’s current implementation & specification, check out the BOLD Github repository!
• Get first-hand experience running an honest or malicious BOLD validator (i.e. either to defend a network or attack a network) by following this guide.
• Check out the BOLD testnet block explorer!
• Read the updated BOLD whitepaper, which covers the formal specifications of BOLD alongside mathematical safety proofs!
• A deep dive into how BOLD is implemented can be found in the Technical Deep Dive into Arbitrum BOLD
• If you’re interested in the economics underlying BOLD disputes, see “The Economics of Disputes in Arbitrum BOLD”

In addition, we’ll be having a live AMA on “Uncovering BOLD & Permissionless Validation” on Thursday, April 18th at 11:30 AM ET here, where the big brains behind BOLD will answer questions.