Introduction to Polygon 2.0 Architecture | Comprising four protocol layers, what roles do they play respectively?

In the previous article introducing Polygon 2.0, the official announcement was made that Polygon PoS chain will be upgraded to become "zkEVM Validium" using zero-knowledge proof technology. Today, Polygon's engineering team shared the proposed architecture of Polygon 2.0, aiming to provide unlimited scalability and unified liquidity to realize Polygon's vision as the internet value layer.

1/ Today, we are excited to propose the Polygon 2.0 architecture, designed to provide unlimited scalability and unified liquidity, thus transforming Polygon into the Value Layer of the Internet!

Read the blog 👇🏽 or keep scrolling 🧵https://t.co/sShy6R1E6R pic.twitter.com/BTdwkri4nI

— Polygon (Labs) (@0xPolygonLabs) June 29, 2023

Introduction to the Architecture of Polygon 2.0

According to Polygon's introductory article, the architecture of Polygon 2.0 consists of 4 protocol layers, each playing different roles and achieving specific functions, including:

• Staking Layer
• Interop Layer
• Execution Layer
• Proving Layer

Staking Layer of Polygon 2.0

Let's first talk about the Staking Layer, which is a PoS-based protocol layer that allows participation in Polygon's decentralization process through the Polygon token MATIC. It achieves this goal through a highly decentralized validator pool and built-in re-staking models.

The Staking Layer operates two smart contracts on Ethereum:

• Validator Manager: Manages all public validator pools available for Polygon's use.
• Chain Manager: Manages the validator set of individual Polygon chains. Each Polygon chain has its own chain manager contract.

Polygon states that the Staking Layer provides immediately usable decentralized capabilities for blockchains on Polygon, allowing blockchain teams to focus on use cases and communities rather than infrastructure.

Furthermore, for validators, the Staking Layer also offers rewards in Polygon tokens and additional token rewards through transaction fees and chains they validate.

Interop Layer of Polygon 2.0

The Interop Layer facilitates cross-chain message passing in the Polygon ecosystem, making the entire Polygon network appear as a single chain to users and accomplishing the following functions:

• Shared access to native Ethereum assets: Cross-chain bridges often require users to mint synthetic versions of Ethereum tokens, creating a nightmare for user experience. The Interop Layer provides cross-chain bridges shared with Ethereum, allowing seamless transfer of native Ethereum assets across chains.
• Seamless composability: The Interop Layer enables near-instant and atomic cross-chain transactions, a core goal of Polygon 2.0's unified liquidity.

The Interop Layer expands on the LxLy protocol used by Polygon zkEVM rollup and borrows the concept of a message queue. Each Polygon blockchain maintains a local message queue in a predetermined format, containing digital asset messages, target chains, target addresses, and metadata.

The message queue has corresponding ZK proofs. Once a specific queue's ZK proof is verified on Ethereum, any messages in the queue can be securely used by the receiving chain and address.

Based on this design, Polygon proposes incorporating a unique aggregator component to further enhance cross-chain transactions. The aggregator sits between Polygon and Ethereum, providing two services:

1. Represent the received ZK proofs and message queues, e.g., Merkle Root.
2. Aggregate ZK proofs into a single proof and submit it to Ethereum for verification.

Once the aggregator accepts the ZK proofs, the receiving blockchain can more optimistically accept messages because the ZK proofs ensure finality and consistency, enabling seamless cross-chain interactions. By aggregating ZK proofs, the aggregator significantly reduces the gas consumption needed for proof verification on Ethereum.

Execution Layer of Polygon 2.0

The Execution Layer enables any Polygon blockchain to produce sequentially ordered batches of transactions, known as blocks. This protocol layer is used in a similar way across various blockchain networks like Ethereum, Bitcoin, etc., making it relatively standardized.

The Execution Layer includes multiple components such as:

• P2P: Allows nodes, validators, and full nodes to discover and exchange messages with each other.
• Consensus: Enables validators to reach consensus on a single view of the world.
• Mempool: Collects transactions submitted by users and synchronizes them among validators.
• Database: Stores transaction history records.
• Proof Generator: Generates proof data required for zero-knowledge proofs.

Polygon believes that given the relatively standardized nature of this layer but the complexity in implementation, existing high-performance implementation solutions like the Ethereum client Erigon should be reused as much as possible.

Proving Layer of Polygon 2.0

The Proving Layer is an efficient and flexible zero-knowledge proof protocol that generates proofs for all transactions on every Polygon blockchain. It consists of the following parts:

• Common prover: This prover provides a clean interface designed to support any transaction type. Additionally, using a single prover makes proof aggregation and verification simple and efficient.
• State machine constructor: The constructor allows developers to build a state machine through an easy-to-use interface. Being modular, it allows developers to customize parameterized state machines, making it easier to build, test, and audit large and complex state machines.
• State machine: The state machine simulates the execution environment and transaction format proven by the prover. The state machine can be implemented using the aforementioned constructor or in a fully customized manner. Polygon's ZK team provides two state machine implementations, zkEVM and MidenVM, and the community can construct other implementations such as zkWASM.