Optimistic Rollups v zk Rollups: A Complete Guide to Layer-2 Solutions
TL;DR
This article compares the two types of Rollups - Optimistic and zk Rollups. While Optimistic Rollups ensure the scalability of blockchains by rolling up transactions, allowing swift submission, and validating before finalizing the transactions, zk Rollup comfirms the validity of every rollup transaction at the point of submission, ensuring high security. Also, note that both Rollups are EVM-compatible, making them a readily adoptable option for deploying Ethereum-based dApps.
Dive into the article for a comprehensive explanation.
Introduction
In the world of blockchain technology, scalability is a big issue because only scalable blockchains attract users. The cryptocurrency and blockchain landscape generally attracts users who want to perform swift financial transactions. Therefore, blockchain must provide users with this to fulfill one of its promising features and remain an appealing alternative to traditional financial systems.
However, the leading blockchain, Ethereum, was not initially designed to meet mass usage. Hence, when blockchain adoption grows drastically, enhancing scalability and eliminating system congestion becomes a significant concern. Users also have to pay a very high gas fee, which keeps increasing as the demand to complete transactions on Ethereum increases.
With all these, it was evident that not only will Ethereum fail to meet the massive market, but it may also compromise on a leading feature of a blockchain and frustrate users. This led to the call for a scalable Ethereum, or perhaps, a scalable blockchain, and to answer the call, Rollup technology was invented to ease congestion on Ethereum by simply rolling up multiple transactions into one batch off-chain and submitting it to the mainchain (which is Ethereum).
What are Rollups and how do they work?
Rollup technology was primarily introduced to improve transaction throughput on Ethereum by combining several transactions into a batch and sending the batch to the Ethereum blockchain for validation. Essentially, this reduces the number of transactions that would ordinarily be sent to Ethereum, and by doing that, Ethereum can handle those batch transactions swiftly.
Rollups work on separate Layer 2 blockchains that are compatible with Ethereum. These L2 blockchains are used to verify signatures, run contracts, perform other tasks in smaller sizes, and execute those tasks before sending them to Ethereum (a Layer 1 blockchain) to store transaction data. Given that only the proof (a smaller transaction size) is posted on-chain, using rollups results in a significant reduction in gas fees.
There are two types of Rollups:
• Optimistic Rollups
• zk Rollups
What are Optimistic Rollups, and how do they Compare to zk Rollups?
Optimistic Rollups v zk Rollups
Comparing Optimistic Rollups and zk Rollups ensures that dApp developers make informed decisions when developing their applications. Depending on the nature of your project, choosing which of the two to opt for will be determined by highlighting the features you should prioritize over others.
Once you have determined which rollup technology is most suitable for your dApp, explore comprehensive and cost-effective access to both Optimistic Rollups and zk-Rollup RPC services on Chainnodes. Chainnode is a leading RPC provider offering developers extensive access to build applications on any Layer1 and Layer2 blockchains for free through the Chainnodes' Starter Package.
Let's talk about Optimistic Rollups
Optimistic Rollups are one of the most promising Layer2 scaling solutions for Ethereum and other blockchains. Optimistic Rollups increase transaction throughput and reduce cost by aggregating multiple transactions off-chain and bonding them into a single batch that is then submitted to the Layer 1 blockchain.
These EVM-compatible Rollups are optimistic because the technology assumes that all transactions submitted to the Rollup are valid and innocent until proven otherwise. One leading benefit of this structure is that, compared to other Rollups, it allows for easy and swift submission of blockchain transactions.
A sequencer or validator can eventually contest the trueness of transactions. To validate transaction genuineness, Optimistic Rollups distribute Merkle roots to a network of external validators who must ensure correctness before validating a transaction. When validators suspect that any transaction is malicious, they publish fraud proof to contest the validity of such transaction. This opens up a "challenge period" and the transaction is rolled back to the state before validation.
Of course, the ecosystem rewards external validators for maintaining the system's security. Contrarily, validators are punished for acting maliciously or compromising the chain's security, either through delay or negligence.
Use cases: Optimistic Rollups are used by notable blockchains and projects, which include Arbitrum, Base, Bora Network, Optimism (OP Mainnet), Mantle, and several others.
What are zk Rollups
zk Rollups (Zero-Knowledge Rollups) is another type of Layer2 scaling solution designed to enhance Ethereum's scalability. Like the Optimistic Rollups, zk Rollups also aggregate transactions off-chain, roll them into one batch, and submit the batch to the Layer 1 blockchain. However, this technology maintains significant differences from Optimistic Rollups.
zk Rollups maintains security by generating cryptographic proof at the point when transactions are submitted; hence, when users initiate transactions, the network verifies validity using zero-knowledge succinct non-interactive arguments of knowledge (zk-SNARKs) or zero-knowledge scalable transparent argument of knowledge (zk-STARKs). These tools ensure the blockchain can confirm transactions without revealing users' data.
Use cases: Similarly, zk Rollups enjoys notable adoption and is used by projects like zkSync, Polygon zkEVM, and Starkware.
What to consider when choosing between Optimistic Rollups and zk Rollups for dApps: Key System Components
• Security
Optimistic Rollups: The security of Optimistic Rollups is in the hands of the sequencer or validator, who must act without delay whenever a malicious node or invalid transaction is noticed. Given that transactions are presumed to be valid and true at the point of submission it becomes easy for bad actors to compromise the system integrity. Also any delay or failure on the part of the sequencers or validators means that invalid or false transactions will be submitted and validated.
zk Rollups: zk Rollups, on the other hand, boast of high-level security because transactions are verified and validated at the point of submission using the zero-knowledge cryptographic tools. Hence, it is less vulnerable to attack and will not likely validate malicious transactions.
• Scalability
Optimistic Rollups: Optimistic Rollups enjoy higher scalability than other Rollups because transactions are presumed innocent and valid, resulting in 10-100x faster throughput compared to L1 blockchian. This means that users can submit transactions without delay. However, the issue of finality is a different ball game.
zk Rollups: While zk Rollups is also a scalable option for Layer1 blockchain compared to Optimistic Rollups, zk Rollups experience notable delays in validating transactions. This is because transactions are validated at the point of submission. The good side is that zk Rollups enjoy faster finality than Optimistic Rollups.
• Cost
Optimistic Rollups: Regarding transaction and computational costs, Optimistic Rollups offer users and node validators a more cost-effective offer. Fast submission of transactions prevents system congestion, which in turn has a positive impact on transaction fees. Similarly, the Optimistic fraud-proof method used to challenge suspicious transactions by sequencers and validators is compatible with any Layer 2 node, eliminating additional hardware costs.
zk Rollups: On zk Rollups, indexes represent easily compressible user data. This reduces the cost of submitting transactions to the Layer 1 blockchain; however, validity proof requires additional hardware, making running the validation node less cost-effective. Notably, users also enjoy low transaction fees on zk Rollups.
• Privacy
Optimistic Rollups: Transacting on Optimistic Rollups is the same as Layer 1 - wallet address is available for the public. This can be used by anyone to connect your transaction on Layer 2 chain to your mainchain (Layer 1) account.
zk Rollups: Unlike Optimistic Rollups, zk Rollups boast of higher privacy by ensuring that only sender and receiver have access to the details of the transactions. Also, users' Layer 2 wallet addresses are not connected to their main account, but it is vital to note that public keys are required to sign transactions.
• Finality
Optimistic Rollups: As mentioned earlier, finalizing transactions on Optimistic Rollups is prone to delay because external validators can challenge the validity of transactions, which opens a challenge period, particularly for malicious or suspicious transactions. Once a challenge period is opened regarding a transaction, finalizing the transaction takes 7 days.
zk Rollups: zk Rollups enjoy speedy finality as the correctness or otherwise of all transactions is already validated at the submission point.
• Smart Contract
Optimistic Rollups: One significant advantage of optimistic rollups is the ease of deploying applications on the chain without additional programming due to the Optimistic Rollups' built-in smart contracts.
zk Rollups: Though zk Rollups also allow for the deployment of applications, it is often consider a complex option. However, developers can still leverage its EVM-compatibility features to deploy apps quickly.
Conclusion
Choosing between the two rollups depends extensively on the nature of the application you are developing. For instance, while major decentralized exchanges like Uniswap opt for Optimistic Rollups due to their ability to facilitate transactions swiftly and ensure high throughput, we've seen the adoption of zk Rollups by application that requires high security.
Irrespective of your preferred Rollups, the good news is Chainnodes presents you an offer to start developing your decentralized applications on either Optimistic Rollups or zk Rollup for free. Check it out to enjoy free archival data, easy application development and deployment, and a 24/7 support center on Telegram.