Polygon 2.0: Polygon PoS -> ZK L2

Polygon Labs

June 20, 2023

Today, the engineering team at Polygon Labs published a proposal to upgrade Polygon PoS to a zkEVM validium, a first-of-its-kind decentralized L2 secured by zero-knowledge (ZK) proofs. This is a major milestone for the Polygon ecosystem, as it would enable Polygon PoS to become more secure, more performant, and a core part of the Polygon 2.0 ecosystem.

The fact that this is not only possible, but practical, is a testament to Polygon's technical leadership. Over the past eighteen months, Polygon Labs has released the fastest ZK proving system in the industry and launched the only EVM-equivalent zkEVM on mainnet.

Now, we propose adding zkEVM technology to one of the most successful chains in existence, with over $2b of on-chain assets, tens of thousands of dapps, and an average of 2.5 million transactions per day. If accepted by the community, this upgrade will mark an incredible technical achievement—the first time that an existing chain (especially of this size and importance) adds ZK proofs to become an L2.

But why is this milestone such an important part of Polygon 2.0 and the Polygon ecosystem? What does it mean for users, developers, and validators? How will Polygon PoS coexist with Polygon zkEVM? What will be the utility of $MATIC in the upgraded chain? Let’s dive in.

Polygon 2.0: A ZK-Powered Future

Last week, we introduced Polygon 2.0, a vision for unlimited scalability and unified liquidity, powered by ZK technology. A core part of the Polygon 2.0 vision is that every Polygon chain should be a ZK L2, but Polygon PoS in its current state is secured by its own validators, not by ZK proofs.

Polygon 2.0 is a huge step forward for the Polygon ecosystem, and it should not exclude Polygon PoS, one of the most successful and widely-used chains in the industry. Many users and developers still prefer Polygon PoS because of its strong ecosystem, network effects and very low fees, often orders of magnitude lower than Ethereum rollups. The strength and activity of Polygon PoS will help bootstrap the rest of Polygon 2.0.

Therefore, we set the goal to upgrade Polygon PoS to enable it to leverage bleeding edge ZK technology and fit into the Polygon 2.0 vision, ideally without changing anything for users or developers. All applications should continue working and fees should stay just as low. The only difference should be higher security for users and seamless interoperability with every other chain in the Polygon 2.0 ecosystem. Enter zkEVM validium.

zkEVM Validium: Low Fees, High Security and Scalability

You can think of a validium as the lower-cost, higher-throughput sibling of a rollup. Rollups, like Polygon zkEVM, leverage Ethereum to publish transaction data and verify proofs, thus fully inheriting its unmatched security and decentralization.

The tradeoff with rollups is that publishing transaction data to Ethereum is expensive and limits throughput. Validiums offer similar security guarantees to rollups (ZK proofs guarantee the validity of transactions) but transaction data is made available off-chain.

This gives validiums two main advantages over rollups:

Significantly lower fees, since they don't consume expensive Ethereum gas, i.e., blockspace to store transaction data.
Significantly higher scalability, since rollups’ throughput is bounded by the amount of transaction data that can be published to Ethereum.

The only additional cost to run Polygon PoS as a zkEVM validium in the long term would be the cost of generating proofs, and Polygon Labs’s ZK teams have already made incredible progress in reducing these costs. On Polygon zkEVM, the cost to prove a 10 million gas batch is just $0.0259, or $0.00005 per transfer.

The tradeoff with validiums is that they must ensure transaction data availability outside of Ethereum, which can be challenging. Fortunately, Polygon PoS already has a decentralized validator set of 100+ validators with ~$2B at stake, which can serve as a highly secure and reliable guarantee of data availability.

What Does This Mean for Users and Devs?

It’s important to note that the proposal will not change the experience of the Polygon PoS network for users or developers.

‍Polygon PoS will continue to be the low-cost destination for users, and the implementation of a ZK tech-stack would not require any retooling of smart contracts for developers. Similar to other Polygon PoS upgrades, node operators and validators would only need to upgrade to the latest version of the Polygon PoS client software.

For validators, the staked token would remain $MATIC and chain economics would not change.

Validators and $MATIC Utility

After the upgrade, existing Polygon PoS validators will play two extremely important roles: guaranteeing data availability and sequencing transactions.

First, the existing Polygon PoS consensus mechanism already guarantees data availability; validators attest that transactions are valid and transaction data is available. After the upgrade, validators will continue to attest to data availability, thus turning Polygon PoS into the first validium with decentralized and secure data availability guarantees.

Second, Polygon PoS validators would operate the chain by deciding which transactions to include in a block and in which order. This is critical to preserve decentralization and means that transaction fees would continue to flow to $MATIC-staked validators. This would make Polygon PoS the first L2 with a decentralized sequencer set.

zkEVM Rollup and zkEVM Validium

Currently, Polygon PoS and Polygon zkEVM rollup are two public networks of the Polygon ecosystem. That would remain the case after the upgrade, with the added benefit of both networks using bleeding edge zkEVM technology, one as a rollup and the other one as a validium.

We believe the two networks can meaningfully coexist and complement each other:

Polygon zkEVM rollup already offers the highest level of security, with the tradeoff of slightly higher fees and limited throughput. It is a great fit for applications that process high value transactions and where security is the priority, e.g. high value DeFi applications.

Upgraded Polygon PoS (zkEVM validium) would offer very high scalability and very low fees. It would be a great fit for applications that have high transaction volume and require low transaction fees, e.g. Web3 gaming and social and micro DeFi.

Conclusion

Last week, we published the vision for Polygon 2.0, aiming to establish Polygon as the Value Layer of the Internet—a foundational protocol that will allow anyone to create, exchange, and program value the same way the Internet allows anyone to create and exchange information.

This upgrade would be an important step toward creating the Value Layer, given that it would allow the entirety of Polygon PoS users, assets, and state to migrate to the Polygon 2.0 ecosystem.

The Pre-PIP is already live on the governance forum. Assuming it gathers significant support, i.e. consensus from the community, a formal PIP (Polygon Improvement Proposal) will be put forward, initiating the PIP-1 and PIP-8 prescribed processes. The PIP will then be discussed on PPG (Polygon Protocol Governance) Calls, governance forum and other public venues in order to gather consensus from all relevant ecosystem participants. If consensus is reached, the implementation could go live on mainnet by the end of Q1 2024.

Polygon Labs may have started the discussion, but the community will lead it. We’d like to encourage every community member to participate. You don’t need to be a researcher, validator, or core developer to be heard.

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Together, we can build an equitable future for all through the mass adoption of Web3!