zkEVM - text book definition : ZK-rollups with EVM compatibility

Let's break that down a bit.

What is an EVM ?

Ethereum Virtual Machine (EVM) is the transaction execution environment on the Ethereum blockchain. EVM is responsible for executing all operations and transactions on the blockchain. The EVM allows the creation & execution of smart-contracts thereby adding 'programmability' to the blockchain. Further, it also manages the state of the Ethereum blockchain. The EVM depends on a decentralized network of nodes to perform the smart-contract operations and compute the final state of the blockchain, to reach a consensus, on its behalf. On the blockchain, the smart-contracts gets compiled to EVM bytecodes, which contains specific instructions called opcodes, that tells the EVM what operations to perform. After the smart-contract computation, the EVM also computes and updates the final valid state of the Ethereum blockchain. Besides smart-contract computation and state computation, the EVM forms the very back bone of the Ethereum network by enforcing all necessary regulations on the blockchain.

Owning to the extensive dependency of the EVM on thousands of nodes to perform the same smart-contract, which essentially means very slow computation and the limited block size of the blockchain, scalability has been a real issue on the Ethereum blockchain. Though proposals were suggested to tackle this issues, those often demanded compromising on the security and decentralisation of the blockchain. This forms the blockchain trilemma : security , scalability and decentralisation - how to improve one aspect without downgrading the other two.

One popular solution, that has been widely accepted and adopted by the blockchain community is Layer 2 scaling.

Layer 2 scaling

This solution proposes to handle transactions off the Ethereum Mainnet (Layer 1 or L1). Taking computation load off the Ethereum Mainnet is one way to scale the blockchain. Take note, any such transactions taken off chain must comply to the decentralized security model of the Mainnet. The most promising layer 2 solution, so far, has been rollups.

Rollups

Rollups allows the users to have their transaction executed on L2 instead of L1. Then several transactions are bundled together and their data is pushed to L1. This means, for what used to be hundreds of transaction on the L1 Ethereum Mainnet, we can now have a single transaction depicting the data of those hundred transactions. This would drastically bring down the gas fees and improve the speed of transactions.

And the buzz word in the industry - zkRollups !

zkRollups !

but what’s zk?

Imagine a situation. you are in a math class and you want to convince your buddy that you know a specific formula, but you do not want to reveal the formula as such to them ? How do you this is possible ?

Let's try something. Allow your buddy to give you multiple problems based on the formula. Now since you already know the formula, you can solve these problems and reveal only the final answers to your buddy.

Voila! you just proved that you know the specific formula, yet you did not give up the formula as such.

This exactly is what Zero Knowledge Proofs(ZKP) aims to achieve. ZKP allows one to prove that they know a piece of information without ever really really revealing the information or any other details about it. At the core, ZKP is an interaction between a prover and a verifier, where the former can convince the latter that they know of a particular secret(witness) without revealing any other details about it. Thus it is a proof of knowledge.

This very nature of ZKPs make it the industry favourite for privacy and security sensitive applications. Integrating this super-amazing cryptography protocol to rollups, we have zkRollups, which uses zero knowledge proofs to determine the validity of transactions.

Now think about this, every L2 scaling solution, including zkRollsups, are defined by an immutable smart-contract on the L1. This smart-contract dictates what the L2 is supposed to do. This is done by implementing a subset of the L1 EVM within the smart-contact.

Why only a subset !? That's because defining a full Ethereum client inside an EVMcode would demand an unacceptably high amount of over head. Thus the L2s have a defined set of operations that they can perform. This means that not everything that are executable on L1 are executable on L2. This make L2s pretty much application/use-case specific.

until we have zkEVMs.

zkEVMs promise to push over these limitations enabling a wide range of EVM functionalities on zkRollups. It targets to achieve EVM equivalence on L2 networks. EVM equivalence aims for L2 solutions and all of its modules to be completely compliant with the formal definition of the protocol. In such a case, any bytecode that can be run on L1 can also be run on its L2 counterparts without any compatibility limitations.

zkEVMs are virtual machine setups on L2s capable of executing transaction off chain, computing the final state based on the current state and the contract transaction. Once this computation is complete zkEVM uses a proving circuit to generate a zero knowledge proof. This proof along with the initial and final state of the zkEVM is then submitted to an Ethereum based verifier contract which then validates the legitimacy of the proof and updates the state of Ethereum blockchain.

zkEVMs are of the following types :

• fully Ethereum-equivalent : an absolute replica of Ethereum system, without changing a thing about it

• fully EVM-equivalent : fully equivalent to the EVM, but with considerable differences from the Ethereum structure

• almost EVM-equivalent : compromising on few factors over EVM equivalence

• high-level-language equivalent : takes the smart contract written in any high level language (Solidity , Viper etc) and compiles it to an EVM friendly language.

zkEVMs are defining the future of the Ethereum blockchain. They promise enhanced privacy, as zero-knowledge proofs allow users to execute smart contracts without revealing sensitive information. Plus, improved scalability, as they can handle a larger number of transactions per second compared to traditional Ethereum smart contracts. Further they enable new use cases for smart contracts that were previously not possible due to privacy or scalability concerns.

This holy grail of scaling solution is accelerating with zero brakes and there is no stopping it. LFG !