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Source: Polygon Forum; Author: Baishui, Bitchain Vision
Preface
We invite the community to discuss a proposal to securely connect Polygon PoS to AggLayer using a zero-knowledge (ZK) validator to verify the network’s consensus mechanism, thus establishing the finality of network settlement to AggLayer.This consensus proof is a complement to the pessimistic proof that ensures the security of all chains connected to AggLayer.For more information on pessimistic proofs, see here: Introduction to pessimistic proofs 2
The proof of consensus will be protected by the Plonky3 proof system through SP1 of Succinct Labs, a general purpose zkVM that allows the execution of the AggLayer proof standard Rust.For more information on the collaboration between Polygon Labs and Succinct Labs, see here: SP1 built on Plonky3 will help ensure uniform liquidity 1
This upgrade will bring two direct benefits:
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Aggregate liquidity, users and status through AggLayer to bring greater network effects to users and developers;
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Upgraded bridge experience including permissionless token transfers.
background
A year ago, the community began discussing a proposal that would make Polygon PoS a zkEVM Validium, thereby upgrading the network to L2 powered by ZK.This remains the long-term goal of the final state of Polygon PoS.The challenge to achieve this depends largely on the commitment to maintaining Polygon PoS’s low-cost, Ethereum’s spirit of serving everyone.
The Type 1 zkEVM prover for upgrading Polygon PoS to ZK L2 has been able to prove existing Ethereum blocks at low cost.For Polygon PoS applications, the question now is how to do this on a large scale.
For now, if this discussion is advantageous and subsequent PIPs are accepted by the community, the upgrade will be an intermediate step to becoming a full ZK L2.Connecting Polygon PoS to AggLayer will provide the benefits of a unified bridge while still being able to rely on the hardened security provided by the validator set.
Technical details
If community discussions revolve around this proposal, future PIPs or PIPs will provide appropriate technical specifications.However, from a high level, this upgrade requires at least the following:
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Proof of consensus:A new consensus verification contract will be deployed on Ethereum.This contract will be able to verify whether Polygon PoS has reached a consensus and whether any withdrawal meets the standards set out in the pessimistic proof logic.A proposal is created to add it to the list of available verification contracts for Unified Bridge.(See the practical question below for additional considerations about this.)
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Bridge Implementation:The Unified Bridge contract will be deployed on Polygon PoS.
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PoS Portal:Existing tokens in PoS Portal Bridge will be upgraded to use Unified Bridge, and ownership will be destroyed, eliminating multi-signature control over these tokens.
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Network role:Using a consensus proof design to settle to AggLayer will require some entities to submit the required information.(See the practical question below for additional considerations about this.)
Client Changes
No significant client changes are required to complete this upgrade.While upgrading to Heimdall v2 may be subject to future optimizations, this is not necessary for initial deployment.
Bridge changes
Completing this upgrade does not require changing the StateSync mechanism that supports FxPortal or Plasma Bridge.also:
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Unified Bridge will be deployed as a standalone new bridge.
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Tokens that use PoS Portal mapping will be upgraded to use Unified Bridge instead of FxPortal, and PoS Portal will be deprecated.
Timeline
If the results of this discussion are satisfactory, a formal PIP will be released.The main dependency is to complete production-ready implementation of pessimistic proofs, which is expected to be completed in mid-summer.Once completed, a formal PIP will be released, most likely to be completed in the fall.Following this schedule, assuming the community accepts, connecting Polygon PoS to AggLayer may be done by the end of 2024.
Meanwhile, the core engineers of Polygon PoS expect the upcoming Ahmadabad hard fork to be deployed in July, and Heimdall v2 is expected to be launched sometime later.Currently, neither upgrade is a dependency that connects Polygon PoS to AggLayer.However, there is another way to implement the consensus proof that requires deeper changes to Heimdall.
Practical Problems
Signature-based consensus proof
This proposal outlines the consensus on using Polygon Plonky3 to represent Polygon PoS, where SP1 zkVM provides Rust’s maintainability and developer speed advantages.Broadly speaking, the goal of proof of consensus is to represent the local chain state.This can also be done by modifying Heimdall to use different signature methods.
For example, if a BLS or ICE-FROST threshold signature was used during consensus, the individual signature could represent the consensus of AggLayer.One benefit of this approach is its simplicity: communication between Polygon PoS and AggLayer can be added as a task to Heimdall, the same process as the current process of submitting a checkpoint to L1.
A potential drawback is that this approach requires deeper changes to the consensus mechanism of the network, which may extend development time.This design will eliminate the need for new network roles.
Network roles that communicate with AggLayer
In order for Polygon PoS to connect to AggLayer using consensus proof of agreement, a new role is required.This role will be responsible for submitting the following information to AggLayer:
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The local bridge status of the network;
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Proof of consensus.
How and who performs this function is an area of active investigation.At a high level, protocol researchers are considering one of the following:
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Allow list addresses to perform this role first, with the goal of making the AggLayer stack free of permissions after it has a chance to harden it;
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The role immediately does not require permission, in which case the network participants will perform this function in exchange for some rewards that have not been quantified yet.If this is the preferred option and there are no other security issues, you need to determine what mechanism to choose this network participant; a potential option is to use the existing leadership choices in Heimdall.
Summarize
With more than 400 million unique addresses, more than $2 billion assets bridged from Ethereum, and tens of thousands of applications, Polygon PoS remains one of the most widely used blockchains in the world.Users and developers love it because it has a strong community, network effects and low fees for everyone, often several orders of magnitude lower than the famous Ethereum L2.
The core developers of Polygon Labs have been focusing on research and development of Ethereum expansion technology for many years; it starts with Polygon PoS.Over the years, they have come to two conclusions: ZK technology is the only practical way to implement verifiable off-chain computing, and aggregation is the only way to achieve multi-chain interoperability without sacrificing chain sovereignty.
The joint efforts of Succinct Labs and Polygon Labs are based on a shared belief that collaboration with open source technologies can build the best public interest.The results of the discussion about the future of Polygon PoS are ultimately in the hands of the community.We once again invite you to analyze, discuss and hope to reach a consensus on implementing the proposal.
