Alchemy University (AU) is an ecosystem for learning how to build and interact with web3 and offers a bootcamp for those interested in learning.The following is a submission to the AU Tech Writers Guild for the Research Deepdive 'ZK-EVM:Beginners guide to pro'.
Scaling Ethereum with zkEVM
Why scale?
In its current state, the Ethereum mainnet is only able to process 15 transactions per second. As the number of people using Ethereum has grown, the blockchain has reached capacity limitations leading to slow processing times and high transaction fees, creating the need for scaling solutions.
The main goal of scalability is to increase transaction speed (faster finality), and transaction throughput (high transactions per second), without sacrificing decentralization or security.
Layer 2 is a collective term for solutions that process transactions off the Ethereum Mainnet (Layer 1) while taking advantage of the robust decentralized security model of Mainnet.
How scale?
A zero-knowledge proof (ZKP) allows someone to publicly verify that they possess specific information without revealing the specifics or details of that information.
Zero-knowledge rollups (ZK-rollups) are Layer 2 scaling solutions that bundle (or 'roll up') transactions into batches that are executed off-chain and only post to the Mainnet a summary of the changes required to represent all the transactions in a batch rather than sending each transaction individually.
They also produce validity proofs to prove the correctness of their changes. The validity proof demonstrates with cryptographic certainty that the proposed changes to Ethereum's state are truly the end-result of executing all the transactions in the batch.
What zkEVM?
The EVM (Ethereum Virtual Machine) is the runtime environment in which smart contracts deployed on the Ethereum network are executed.
A zkEVM (zero-knowledge Ethereum Virtual Machine) aims to replicate the Ethereum environment as a ZK-rollup, allowing developers to build on it like they would on Ethereum.
The "witness" is the knowledge shared (the data) between a prover and a verifier. The prover must prove that they know the witness accurately, and the verifier must be able to assess whether the proponent has knowledge of the witness.
Why zkEVM?
Ethereum isn’t just a blockchain. It’s a rich ecosystem of smart contracts, developer tools, infrastructure, and wallets. It’s a vibrant community of developers, auditors, and users.
The best approach to scaling Ethereum involves preserving compatibility with this ecosystem, and a zkEVM offers users and developers an experience nearly identical to Ethereum Mainnet, just with substantially improved scalability and reduced cost.
But why zkEVM?
Secure scalability
zkEVMs are not burdened by Ethereum’s consensus protocol rules and can optimize for execution speed. zkEVMs also verify correctness of off-chain computation with validity proofs meaning transactions performed by smart contracts on Layer 2 can be reliably verified on Layer 1 without nodes having to re-execute the operations. This can significantly increase Ethereum’s processing speed without reducing security.
Cheaper costs
ZK-rollups also cut down the cost of transaction processing by splitting the cost among users. ZK-rollups can afford to post minimal data to Layer 1 because validity proofs already guarantee the trustworthiness of state transitions. The zkEVM may even omit transaction inputs and publish only final state changes, further reducing CALLDATA requirements.
Increased Privacy
The use of zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Arguments of Knowledge) in the zkEVM can provide a higher level of privacy and confidentiality for smart contract transactions.
Network effects
The primary motive behind constructing zkEVMs is to exploit the network effects of Ethereum and offer users and developers an experience nearly identical to that of the Ethereum Mainnet.
Why bad?
Complexity
The implementation and utilization of zkEVM, being a new and complex technology, requires specialized knowledge and expertise. This may lead to potential vulnerabilities in the code and restrict the number of developers who can work with the technology.
Centralization
There is a risk that zkEVM could lead to centralization of the Ethereum network if only a few entities are able to provide the specialized hardware and software required to use the technology.
Who zkEVM?
Type-1 zkEVMs**:** fully equivalent to Ethereum zkEVM Type-1s are expected to be fully equivalent to Ethereum, with no changes made to their state or transaction trees, hash codes, or any other logic within their consensus. Type-1 zkEVMs will be fully compatible with all Ethereum-native applications but require more prover time, as no unique reworking is done to make proof generation faster.
Type-2 zkEVMs: EVM (not Ethereum) equivalence Type-2 zkEVMs will lower the bar a little, aiming for EVM-equivalence instead of Ethereum-equivalence. zkEVM Type-2s would look like Ethereum on the outside but will have slight modifications on the inside to facilitate development and speed up proof generation. In this kind of rollups, a few applications may be incompatible. However, type-2 zkEVMs will still suffer slower prover times. Type-2.5 zkEVMs could therefore improve prover time by increasing gas costs.
Type-3 zkEVMs: departing from EVM zkEVM Type-3s would not be fully EVM-equivalent as this type prioritizes the ease of placing an EVM-like system within ZK-rollups. This involves specific changes to make building easier and improve proof generation. While Type-3 zkEVMs could be compatible with most applications, some of them may require rewriting.
Type-4 zkEVMs: close cousins to the EVM zkEVM Type-4s would be equivalent to high-level languages only, not the EVM itself. Skipping the process of providing zero-knowledge proofs for each stage of EVM execution would therefore reduce costs and encourage decentralization, as well as improve proof-generation time. However, this would make Type-4 zkEVMs less compatible with several applications. Contract addresses will most likely change when moving applications to the EVM, and it will be impossible to carry over several debugging infrastructures.
Notes on zkEVM categories
The categorization scheme here is not absolute as in the future Ethereum will undergo changes that will make it more zk-SNARK friendly, likely upgrading any zkEVM that falls into either of these categories.
Wen zkEVM?
Taiko is a fully decentralized, Ethereum-equivalent ZK-Rollup (Type-1 zkEVM). Launched Alpha-1 Testnet in Dec 2022, launched Alpha-2 Testnet aka Askja in March 22nd, 2023.
Polygon zkEVM launched on Mainnet Beta on March 27, 2023, it is a Type-3 zkEVM that is working towards becoming a Type-2 zkEVM.
https://bridge.zkevm-rpc.com/login
Immutable zkEVM is a zkEVM powered by Polygon zkEVM technology that was announced on March 20, 2023 and is set to fully launch at the end of Q2 2023.
zkSync Era is a Type-4 zkEVM that launched Mainet on Mar 24 2023.
https://portal.zksync.io/bridge
Scroll is a Type-2 zkEVM that announced the Scroll Alpha Testnet on Goerli on Feb 27 2023,and according to the roadmap, Mainet is up next.
Linea is aType-2 zkEVM that released its public testnet on March 28, 2023.
StarkNET is a Type-4 zkEVM and has already launched its Alpha version.
Much wow
zkEVM is the holy grail for scaling thanks to its easily verifiable nature and compatibility with EVM.
The next few months will be exciting as multiple zkEVMs launch on mainet.