The growth of Ethereum has posed challenges related to its scalability. As the number of users increases, the blockchain has reached capacity limits that requires users to pay more fees. So, scaling solutions for Ethereum born is inevitable. Polygon (MATIC) – a layer-2 scaling solution designed to fix Ethereum’s scalability issues recently announced the launch of zkEVM, the first zero-knowledge scaling solution in the world, which is fully compatible with Ethereum.
What is zkEVM?
zkEVM (zero-knowledge Ethereum Virtual Machine) is a virtual machine that generates zero-knowledge proofs to verify the correctness of a statement (including the validity of input and output data). Overall, zkEVM is a product that supports the execution and scaling of smart contracts created by zero-knowledge technology.
zkEVM is a part of zero-knowledge rollups, a technology that handles layer-2 scalability on Ethereum by processing off-chain transactions. It will bring transactions created on the main blockchain outside and process them on a separate Rollups layer, then the processed data will be rolled up into a single block, which is sent to layer 2 for verification. ZK-Rollups, however, does not need supervision because once a block is verified, users’ assets are always guaranteed to be recoverable even if the operators refuse to cooperate.
The initial ZK-rollups lacked the ability to execute smart contracts and were limited to simple payments and token swaps. However, with the advent of zero-knowledge virtual machines compatible with EVM, ZK-rollup is starting to support Ethereum dApps.
The lack of compatibility between smart contracts poses liquidity challenges and zkEVM was born to solve those problems and at the same time support Ethereum-based Dapps expanding to layer 2 ZK-Rollups.
Polygon zkEVM
Polygon zkEVM is a decentralized Ethereum Layer 2 scalability solution that uses cryptographic zero-knowledge proofs to offer validity and quick finality to off-chain transaction computation, also known as a ZK-Rollup. zkEVM will optimize the validation process, improve user experience and interoperability with the EVM virtual machine on Ethereum, and extend the ecosystem for Polygon as well.
Polygon zkEVM uses zero-knowledge proofs as validity proofs in the transaction. Although layer 2 zero-knowledge proofs technology is developed based on complex algorithms to provide authenticity and finality for off-chain transactions, the validity proofs will be very easy to verify. The basic idea of zkEVM is to create an EVM circuit to constrain the EVM (state machine) and prove that all the execution logic of the EVM is correct.
Advantages
Cost savings
- zkSNARK footprint size in L1 for user cost optimization
- Fees reduction of 90% with on-chain data
- Lowers total cost of usage for end users for a better user experience
High performance
- Fast network finality with frequent validity proofs
- Use of Polygon Zero technology, the fastest ZK proof in the world
- Recursive STARK for extreme scalability
- Developers can create different types of dApps for a variety of user experiences
EVM equivalence
- Deployment onto EVM without changes in code
- All EVM opcodes will be supported
- Allows developers to focus on improving code rather than re-writing it
Security
- Ethereum security inherited in L2 with the additional benefit of L2 batching for scaling
- ZK proofs ensure transaction validity and safeguards user funds
- Assurance that information stored cannot be changed or corrupted
Polygon zkEVM architecture
Overview
Polygon zkEVM handles state transitions caused by Ethereum Layer 2 transaction executions. The main components of zkEVM include:
- Consensus Contract (PolygonZkEVM.sol)
- zkNode
- Synchronizer
- Sequencers & Aggregators
- RPC
- zkProver
- zkEVM Bridge
The skeletal architecture of Polygon zkEVM is shown below:
Consensus Contract
The Proof of Donate (POD) validation mechanism is based on a decentralized auction model to get the right to produce batches in a specific timeframe. In this mechanism, the economic incentives were set up so the validators need to be very efficient in order to be competitive.
The Consensus Contract model was developed to upgrade the Proof of Donation mechanism and provide support for the permissionless participation of multiple coordinators to create batches in Layer 2. These batches are generated from rolled-up transactions of Layer 1. Consensus Contract uses a simpler and preferred technique due to its higher efficiency in handling PoD-related challenges.
The strategic implementation of the contract-based consensus promises to ensure that the network:
- Maintains its Permissionless feature to produce L2 batches
- Is highly efficient, a criterion which is key for the overall network performance
- Attains an acceptable degree of decentralization
- Is protected from malicious attacks, especially by validators
- Maintains a fair balance between overall validation effort and network value
To complete the consensus process, Polygon zkEVM employs two sorts of participants: Sequencers Aggregators.
- Sequencers: propose transaction batches to the network, i.e. they roll-up the transaction requests in batches and add them to the Consensus Contract.
- Aggregators: check the validity of the transaction batches and provide validity proofs. Any permissionless Aggregator can submit the proof to demonstrate the correctness of the state transition computation.
zkNode
zkNode is an important piece of software in running any zkEVM nodes. It is a client that the network requires to implement the synchronization and govern the roles of other parts in the network (such as Sequencers and Aggregators). Polygon zkEVM participants will choose how they participate:
- As a node to know the state of the network, or
- As a participant in the process of batch production in any of the two roles: Sequencer or Aggregator
zkProver
All the rules for a transaction to be valid are implemented and enforced in the zkProver. The zkProver performs complex mathematical computations in the form of polynomials and assembly language which are later verified on a smart contract. Those rules could be seen as constraints that a transaction must follow in order to be able to modify the state tree or the exit tree. zkProver is the most complex module that requires development of two new programming languages to implement the needed elements.
LX to LY Bridge
LX to LY Bridge serves as a bridge connecting Layer 2 to Layer 1 that uses zkEVM Bridge technology to increase flexibility and interoperability. As a result, this bridge allows the transfer of assets even though these assets have been rolled up many times.
Final words
Ethereum’s Shanghai hard fork will be released. This hard fork is expected to help Ethereum improve on-chain operations, user experience and reduce transaction fees on Layer 2. Thus, Polygon, which is one of the first layer 2 of Ethereum and will soon deploy zkEVM technology, clearly has a lot of potential for growth.