As Ethereum’s popularity soars, it has encountered significant challenges in scalability, slow transaction times, and high gas fees. These issues have highlighted the need for effective layer-2 scaling solutions that can enhance the performance and user experience of the Ethereum ecosystem without compromising its security and decentralization. Among the prominent contenders in this space are zkSync and Optimism, two layer-2 solutions that offer unique approaches to address Ethereum’s scalability concerns.
What are rollups?
Rollups are layer-2 scaling solutions designed to address the scalability challenges of blockchain networks, particularly Ethereum. Rollups achieve this by aggregating and compressing transaction data into a single batch and then submitting them to the main blockchain for final verification.
Rollups allow for efficient and cost-effective transactions while preserving the security and decentralization of the underlying mainnet. They contribute to the continued growth and adoption of decentralized applications on Ethereum and other blockchain platforms.
There are different types of rollups, including optimistic rollups and zk-rollups. These variations in rollup implementations stem from differences in transaction verification and dispute-handling mechanisms.
zkSync is a layer-2 scaling solution for Ethereum that utilizes zero-knowledge rollups (zk-rollups) to address the scalability challenges of the Ethereum blockchain. With zkSync, transactions are processed off-chain and then aggregated into a single proof submitted to the Ethereum mainnet for verification. This approach allows for significant improvements in transaction throughput, reduced fees, and enhanced privacy while maintaining the security and decentralization of the Ethereum network.
How does zkSync work?
zkSync verifies transactions through zkSNARKs, which stands for Zero-Knowledge Succinct Non-Interactive Argument of Knowledge. zkSNARKs allow zkSync to provide cryptographic proof that transactions are valid without revealing sensitive information.
In zkSync, transactions are executed off-chain within the zkSync layer-2 network. These transactions include transfers of assets, smart contract interactions, and other operations. Once the transactions are processed off-chain, they are grouped into a batch.
To verify the validity of the batched transactions, zkSync uses zkSNARKs, a type of zero-knowledge proof. Zero-knowledge proofs allow the prover (in this case, zkSync) to prove the validity of a statement without revealing any underlying data or information. zkSNARKs specifically provide succinct and non-interactive proofs, meaning they are highly efficient and do not require interaction between the prover and the verifier.
The zkSNARKs in zkSync provide proof that the batch of transactions executed off-chain is valid according to the rules and logic of the zkSync protocol. ZkSync’s smart contracts generate this proof and submit them to the Ethereum mainnet, where the Ethereum network’s validators verify it.
Validators on the Ethereum mainnet can verify the zkSNARKs proof without reprocessing the entire batch of transactions. They only need to verify the validity of the proof itself, which is a computationally efficient process.
Once the Ethereum validators verify the zkSNARKs proof, the corresponding state changes are applied to the Ethereum mainnet. This process ensures that the transactions executed within zkSync are securely and reliably verified without compromising the privacy or confidentiality of the transaction details.
Considerations and limitations of zkSync
While zkSync offers significant advantages for scaling Ethereum applications, there are some considerations and limitations to be aware of.
Complexity and Cost of Implementing Zero-Knowledge Proofs (ZKPs)
Implementing zero-knowledge proofs (ZKPs) can be complex and resource-intensive. It requires specialized knowledge of cryptography and significant computational resources. Developing and verifying the correctness of ZKPs can be challenging and time-consuming. Additionally, the cost associated with implementing ZKPs can be relatively high, which may pose a barrier to entry for some projects and developers.
Potential Privacy and Data Availability Challenges
While zkSync provides transaction privacy through ZKPs, there may be challenges related to privacy and data availability. Zero-knowledge proofs ensure that transaction details remain confidential, but this can also limit the ability to track and audit specific transactions. Additionally, the reliance on off-chain processing and the aggregation of transactions into a single proof introduces the need for proper data availability mechanisms. Ensuring the availability and integrity of off-chain data can be a critical consideration for the overall security and trustworthiness of the system.
The Optimism Network utilizes optimistic rollups as its scaling technology. It aggregates multiple transactions into a single batch, processes them off-chain, and then submits a single proof to the Ethereum mainnet for validation. This approach significantly improves the scalability of Ethereum by allowing for faster and more cost-effective transactions while maintaining the security and decentralization of the underlying Ethereum network.
How does Optimism work?
The Optimism network verifies transactions using the Optimistic Virtual Machine (OVM). The OVM is a layer on top of Ethereum’s existing infrastructure that enables the execution and verification of smart contracts on the Optimism network.
In the Optimism network, the layer-2 chain, a sidechain or roll-up that operates independently of the Ethereum mainnet, processes the transactions. The layer-2 chain can handle many transactions and execute smart contracts more efficiently than the mainnet.
Once processed, the results are stored and bundled into what is known as a “state root.” This state root represents the updated state of the layer-2 chain after the execution of the transactions.
The layer-2 periodically submits the state root to the Ethereum mainnet, where validators verify it. Validators check the validity of the state root and ensure that the transactions executed on the layer-2 chain comply with the rules and logic defined by the Optimism protocol.
If the state root is valid and accepted by the mainnet, it becomes part of the blockchain’s history. This finalizes the transactions and updates the global state of the Optimism network on the Ethereum mainnet.
If an invalid or fraudulent transaction is detected, users or validators can submit fraud proofs to challenge and prove the invalidity of the transaction. In such cases, the Optimism protocol can revert the state changes and rectify inconsistencies.
Drawbacks and Considerations of Optimism
Slower Transaction Finality Compared to Some Solutions
While Optimism offers significant scalability improvements, it is essential to consider that the finality of transactions may be slow. Due to the nature of optimistic rollups, there is a period during which validators can challenge transactions and potentially revert. This delay in finality may not be suitable for time-sensitive applications that require immediate confirmation.
Dependency on Ethereum Mainnet for Security and Final Validation
As a layer-2 solution, Optimism relies on the Ethereum mainnet for security and the final validation of transactions. While this ensures a robust security model, it also introduces a level of dependency on the mainnet. Any disruptions or vulnerabilities in the Ethereum mainnet could impact the overall functionality and security of Optimism.
Here’s a table summarizing the comparative analysis between zkSync and Optimism based on the discussed factors:
|Full compatibility with Ethereum
|Full compatibility with Ethereum
|Strong security with ZKPs
|Vulnerable to censorship attacks
|Low for finality
|Low for users
|Zero-knowledge proofs (ZKPs)
|Requires adaptation and knowledge
|Fully compatible with EVM
Optimistic vs. zk-rollups: Scalability and Costs
Optimistic rollups have an advantage in handling higher transaction throughput, making them suitable for applications that require fast and frequent transactions. However, this comes at the cost of higher gas fees for submitting the batches to the Ethereum mainnet.
On the other hand, zk-rollups are more efficient regarding gas savings, resulting in lower transaction costs for users. However, they have higher computational costs due to generating and verifying zero-knowledge proofs. This process can impact the process transaction speed on the rollup chain.
When considering costs, optimistic rollups may be more accessible to developers and users due to their compatibility with existing Ethereum infrastructure. Developers can leverage their existing smart contracts without needing modifications, and users can use their regular Ethereum wallets and tools. On the other hand, zk-rollups may require developers to rewrite their smart contracts in a specific language and users to adopt compatible wallets or browser extensions.
ZkSync 2.0, launched on “baby-alpha” in October 2022, brought significant improvements to zkSync 1.0, including EVM compatibility and smart contract support. In February 2023, zkSync 2.0 was rebranded to zkSync Era, while zkSync 1.0 was renamed zkSync Lite.
Optimistic vs. zk-rollups: Security
Optimistic rollups risk censorship attacks, where a malicious sequencer or validator can manipulate or delay the submission of valid transactions to the Ethereum main chain. This action can disrupt the intended transaction flow and potentially harm users’ funds. Optimistic rollups rely on users and validators to actively monitor the side chain and challenge any fraudulent transactions within a specified timeframe. If no one challenges a fraudulent transaction, it can be finalized on the main chain, leading to user financial losses.
On the other hand, zk-rollups offer inherent protection against censorship attacks since the submission and verification of transactions occur off-chain. The zero-knowledge proofs used in zk-rollups guarantee the validity of transactions before they get on the main chain. They eliminate the need for users and validators to monitor the side chain and challenge fraudulent transactions actively. However, zk-rollups have a trusted setup assumption. Participants must generate and destroy secret parameters to create the zero-knowledge proofs. Malicious actors could create fake proofs and potentially steal users’ funds if these parameters are compromised or leaked.
It is important to note that optimistic rollups and zk-rollups have security trade-offs and assumptions. While zk-rollups offer stronger guarantees against censorship attacks, they rely on the integrity of the trusted setup. Although susceptible to censorship attacks, Optimistic rollups can be more resilient in scenarios where the trusted setup of zk-rollups is compromised.
When evaluating the security of rollup solutions, it is crucial to consider the specific risks and trade-offs involved and the level of trust placed in different system components. Audits, ongoing research, and community scrutiny are essential for ensuring the security of both optimistic rollups and zk-rollups.
Optimistic vs. zk-rollups: Latency
Optimistic rollups offer low latency for users regarding transaction confirmation. Users can receive near-instant confirmation from the layer-2 network without waiting for the main chain. This process allows for a seamless and efficient user experience. However, optimistic rollups have higher latency for finality. After submitting transactions to layer-2, users must wait for a challenging expiration period before the main chain finalizes their transactions. The length of the challenge period can vary depending on network congestion and security parameters. It typically ranges from minutes to hours.
In contrast, zk-rollups have higher latency for users. Transactions in zk-rollups need to generate and verify zero-knowledge proofs on the side chain before users receive confirmation. This process takes additional time compared to optimistic rollups. However, zk-rollups have low latency for finality. Once the zero-knowledge proofs are generated and verified, the Ethereum mainnet finalizes them immediately without needing a challenging period. The finality time in zk-rollups can range from seconds to minutes, depending on the block time and gas price.
Optimistic vs. zk-rollups: Privacy
Optimistic rollups offer low privacy for users since they require the disclosure of transactions and signatures on both the side and main chains. These transactions are publicly visible, allowing anyone to observe and analyze them. As a result, there is potential for third parties to link these transactions to users’ addresses and identities, compromising privacy.
In contrast, zk-rollups provide high privacy for users by utilizing zero-knowledge proofs. With zk-rollups, transactions and signatures are concealed on the side and main chains. Only the sender and receiver of a transaction possess knowledge of its details, ensuring a higher level of privacy. As a result, it becomes challenging for external parties to link these transactions to specific users’ addresses or identities. Using zero-knowledge proofs enhances the privacy of transactions and provides a higher level of confidentiality.
However, it’s important to note that zk-rollups may have particular privacy limitations. For example, users typically must register their public keys on the side chain before conducting transactions. While this registration process does not expose transaction details or user identities, it can provide some information about users’ activity patterns and balances. It’s crucial to consider these privacy considerations when evaluating the level of confidentiality desired for a particular use case.
The choice between optimistic rollups and zk-rollups regarding privacy depends on the specific privacy requirements of the project or application. zk-rollups offer stronger privacy guarantees by hiding transaction details, while optimistic rollups have lower privacy due to transaction visibility.
Both zkSync and Optimism rollups contribute to developing layer-2 scaling solutions for Ethereum, offering innovative approaches to enhance scalability, reduce gas fees, and improve the overall user experience. As the Ethereum ecosystem continues to evolve, advancements and improvements will likely be made to zkSync and Optimism, further enhancing their capabilities and addressing their limitations.
There is no definitive answer to which one is better between zkSync and Optimism rollups. It ultimately comes down to understanding the specific requirements and trade-offs of each solution and choosing the one that best aligns with the needs and priorities of the project.