Why Ethereum L2’s and Zero-Knowledge Rollups are the next big thing: A Technical overview

July 6, 2023

As the Ethereum network continues to experience growing adoption, scalability becomes a crucial concern. In order to overcome the limitations of Ethereum's Layer 1 (L1) and enhance its transaction throughput, Layer 2 (L2) scaling solutions have emerged. Among these, Zero-Knowledge Rollups (ZK-rollups) have gained significant attention. In this article, we will explore the need for scalability, compare sidechains with L2 scaling solutions, delve into Zero-Knowledge Rollups, and shed light on other L2 approaches like Optimistic Rollups and State Channels.

Scalability and the need for Layer 2

Scalability is the ability of a blockchain network to handle a high volume of transactions quickly and efficiently. Ethereum's L1, while groundbreaking, faces scalability challenges due to its limited transaction processing capacity. As the demand for decentralized applications (dApps) and smart contracts increases, the network becomes congested, leading to high fees and slower confirmation times.

Layer 2 scaling solutions aim to address these issues by moving a significant portion of the transaction load off the main Ethereum chain. L2 solutions build on top of the Ethereum L1, leveraging its security while offering faster and cheaper transactions. They enable a higher degree of scalability by processing multiple transactions "off-chain" and later settling them on the main chain as a single transaction, reducing congestion and optimizing efficiency.

Scaling solutions utilize different consensus algorithms, such as Proof-of-Authority, Delegated Proof-of-Stake, or Byzantine Fault Tolerance, providing additional flexibility. Validating nodes on sidechains verify transactions, produce blocks, and secure the network. However, variations in block parameters, like faster block times and larger sizes, can impact decentralization and security. This may result in a concentration of power among a few "supernodes," increasing the risk of collusion or malicious takeovers. To maintain scalability without compromising decentralization, efforts are underway to ensure open access to running full nodes on the Ethereum network, enabling wider participation and promoting a secure and decentralized ecosystem.

Sidechains vs. Layer 2 Scaling Solutions

Sidechains and Layer 2 scaling solutions are two approaches used to achieve scalability in the Ethereum ecosystem. Sidechains, as the name suggests, are separate chains that run in parallel to the Ethereum main chain. They provide scalability by processing transactions independently, reducing the burden on the main chain. However, sidechains often require a level of trust in their validators and can result in a more fragmented ecosystem.

Layer 2 scaling solutions, on the other hand, build directly on top of the Ethereum L1, preserving the security guarantees of the main chain. By leveraging various techniques, such as rollups and state channels, L2 solutions significantly enhance the scalability of Ethereum while maintaining a high level of decentralization and security.

Zero-Knowledge Rollups

Zero-Knowledge Rollups (ZK-rollups) are a type of Layer 2 scaling solution that utilize zero-knowledge proofs to achieve scalability while ensuring data integrity and privacy. ZK-rollups bundle multiple transactions into a single proof, which is then submitted to the Ethereum main chain for verification.

Several projects have implemented ZK-rollups on Ethereum. Polygon zkEVM, zkSync Era, and Loopring are notable examples. These platforms utilize zero-knowledge proofs to provide substantial scalability improvements. By compressing the transaction data into succinct proofs, ZK-rollups enable faster and cheaper transactions without compromising security or privacy.

To give more technical details, validity proofs in ZK-rollups are generated by the operator after performing necessary checks on transactions. These checks include verifying sender and receiver accounts in the state tree, ensuring sufficient funds for the transaction, validating correctness and matching of public keys, and verifying sender's nonce. Once a ZK-rollup node accumulates enough transactions, it creates a batch and prepares inputs for the proving circuit. These inputs consist of a Merkle tree with all the transactions, Merkle proofs for inclusion of transactions in the batch, Merkle proofs for each sender-receiver pair to prove their presence in the rollup's state tree, and intermediate state roots reflecting state updates after processing each transaction. These components are used to construct a concise ZK-proof for validation.

Optimistic Rollups

Optimistic Rollups are another type of Layer 2 scaling solution that operate on the principle of assuming the validity of transactions unless proven otherwise. These rollups allow for off-chain transaction execution and later submit a "rollup" containing the summarized transaction data to the Ethereum main chain.

Projects like Optimism, Arbitrum One, and Base have been actively working on Optimistic Rollup implementations. Optimistic Rollups enable significant throughput improvements while maintaining decentralization and security. They offer near-instant transaction confirmations and lower fees, making them an attractive solution for dApp developers and users.

Here's a brief technical overview about Optimistic Rollups and how they work:

  • Users submit transactions to operators (validators/aggregators) who process them on the optimistic rollup and publish the block on Ethereum.
  • Validators provide a bond and cryptoeconomic incentives to ensure honest behavior, slashing for invalid blocks.
  • Validators execute transactions and compare their state with the operator's proposed state, challenging with fraud proofs if discrepancies occur.
  • Some rollups use a sequencer instead of validators, with greater transaction ordering control and priority access to the rollup chain.
  • Rollup blocks are compressed into calldata and sent to Ethereum for notarization, reducing user fees and storage costs.

State Channels

State Channels provide an alternative approach to scaling Ethereum by enabling off-chain transaction execution between participants. In a state channel, participants create a private off-chain environment where multiple transactions can be executed rapidly and at negligible costs. The final state of the channel is then submitted to the Ethereum main chain for settlement and additional verification.

To understand how State Channels work, let's delve into the technical details:

  1. Opening the Channel: Participants who wish to transact with each other open a State Channel by creating a multi-signature wallet on the Ethereum main chain. This wallet holds the funds that will be used within the channel.
  2. Off-Chain Transactions: Once the channel is open, participants can interact privately by exchanging signed messages off-chain. These messages contain the necessary information to update the state of the channel, such as the new balances of the participants.
  3. State Updates and Dispute Resolution: As participants conduct transactions, they continuously update the channel's state off-chain. To ensure the integrity of the channel, participants may periodically submit signed state updates to the Ethereum main chain. These updates serve as checkpoints, providing a cryptographic proof of the channel's current state.
  4. Closing the Channel: When participants are ready to settle the channel and finalize the transactions, they submit the final state to the Ethereum main chain. The main chain verifies the state update and distributes the funds accordingly.
  5. Dispute Resolution: In case of disputes or malicious behavior by one of the participants, a predefined dispute resolution process is followed. This process typically involves submitting evidence to the main chain, which allows the chain to settle the dispute based on the evidence provided.


Scalability is a fundamental challenge that Ethereum and other blockchain networks face. Layer 2 scaling solutions, including Zero-Knowledge Rollups, Optimistic Rollups, and State Channels, provide promising avenues to address this challenge. These solutions improve transaction throughput, reduce fees, and enhance the overall user experience without compromising the security and decentralization that make Ethereum a robust platform. As Ethereum's ecosystem continues to evolve, the adoption of Layer 2 scaling solutions will likely play a pivotal role in realizing the network's full potential.