zkRollups vs. Optimistic Rollups: Which is Better for Scaling Ethereum?

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As the popularity and demand for decentralized applications (dApps) continue to grow, the scalability of the Ethereum network has become a major concern. One of the most promising solutions to this problem is the implementation of rollups.

Rollups are Layer 2 scaling solutions that allow for the processing of a large number of transactions off the main Ethereum chain, thereby reducing congestion and increasing efficiency. 

There are two types of rollups: zkRollups and Optimistic Rollups. Both have their unique advantages and disadvantages, and the choice between the two depends on the specific needs of each dApp.

In this article, we will take a closer look at zkRollups and Optimistic Rollups and explore the pros and cons of each to determine which is the better option for scaling Ethereum.

What are zkRollups?

zkRollups (Zero-Knowledge Rollups) are a Layer 2 scaling solution for Ethereum that allows for high throughput and low-cost transactions while maintaining the security and decentralization of the Ethereum network.

In a zkRollup, multiple transactions are bundled together and processed off-chain. The resulting transaction data is then hashed and submitted to the Ethereum mainnet, where it is verified using zero-knowledge proofs.

This allows for a high degree of scalability, as the manner is only required to verify the integrity of a single transaction, rather than each individual transaction within the rollup.

The use of zero-knowledge proofs in zkRollups provides a high level of security and privacy. The proofs allow the rollup operator to prove that the transactions in the rollup are valid, without revealing any sensitive data or details about the transactions themselves.

In addition to scalability, zkRollups also offer cost savings compared to on-chain transactions. By processing transactions off-chain, the cost of gas fees is significantly reduced, making it more accessible for users to participate in the Ethereum ecosystem.

Overall, zkRollups are a promising scaling solution for Ethereum, as they provide a high degree of scalability, security, and cost-effectiveness while maintaining the decentralization and trustlessness of the Ethereum network.

How do zkRollups work?

zkRollups (Zero-Knowledge Rollups) work by bundling multiple transactions together off-chain, then submitting a single proof to the Ethereum mainnet to verify the validity of the transactions.

Here is a step-by-step overview of how zkRollups work:

  1. Multiple transactions are grouped together into a bundle by the rollup operator. These transactions are not executed on the Ethereum mainnet but instead are processed off-chain.
  2. The rollup operator generates a zero-knowledge proof that proves the validity of the transactions in the bundle, without revealing any details about the individual transactions themselves.
  3. The zero-knowledge proof is then submitted to the Ethereum mainnet, along with a hash of the transaction data. This is done in a single transaction, which reduces the cost of gas fees compared to individual transactions.
  4. The mainnet verifies the zero-knowledge proof and the hash, ensuring that the transactions are valid and have not been tampered with. If the proof is valid, the transaction is added to the Ethereum blockchain, and the state of the Ethereum network is updated accordingly.
  5. Any user who wants to interact with the rollup can do so by submitting a transaction to the rollup operator. This transaction is processed off-chain, and the resulting state changes are then included in the next rollup submission to the main net.

zkRollups offer a scalable and cost-effective solution for processing transactions on the Ethereum network, while also maintaining the security and decentralization of the blockchain.

Benefits of zkRollups 

zkRollups (Zero-Knowledge Rollups) offer several benefits for the Ethereum ecosystem, including:

  1. Scalability: By processing many transactions off-chain and then sending a single proof to the Ethereum mainnet, zkRollups provide a high degree of scalability. This significantly decreases the burden on the mainnet and enables considerably greater transaction rates per second.
  1. Cost-effectiveness: Transactions in zkRollups are substantially cheaper than on-chain transactions since they do not require the same degree of processing resources. This makes it easier for consumers to join the Ethereum ecosystem and lowers the cost of transaction gas fees.
  2. Security: zkRollups employ zero-knowledge proofs to validate transactions without disclosing any sensitive information about the transactions. This protects users’ privacy and security while also lowering the danger of fraud or assaults on the Ethereum network.
  1. Decentralization: zkRollups are meant to be decentralized, which means that no single party has control over the network, ensuring that it is resistant to censorship and collusion while still maintaining trust.The Ethereum ecosystem’s less-than-perfect character.
  1. Compatibility: Developers may easily transition their apps and smart contracts to the rollup ecosystem since zkRollups are completely compatible with existing Ethereum tools and infrastructure.

zkRollups offer a promising solution for scaling the Ethereum network, while also maintaining its core principles of security, decentralization, and compatibility.

What are Optimistic Rollups?

Optimistic Rollups are a Layer 2 scaling solution for Ethereum that allows for high throughput and low-cost transactions while maintaining the security and decentralization of the Ethereum network.

In an Optimistic Rollup, multiple transactions are bundled together off-chain and submitted to the Ethereum mainnet as a single transaction. However, unlike zkRollups, Optimistic Rollups do not use zero-knowledge proofs to verify the validity of transactions. Instead, they rely on a mechanism called fraud-proof.

Fraud proofs are a mechanism that allows anyone to challenge the validity of a transaction on the rollup. If a fraudulent transaction is identified, a challenge can be submitted to the Ethereum mainnet, which triggers a dispute resolution process.

This process involves a series of time-limited rounds where the transaction is checked and verified by various parties.

If the transaction is found to be fraudulent, the party responsible for the fraudulent transaction is penalized and the transaction is reverted.

How do Optimistic Rollups work?

Optimistic Rollups work by bundling multiple transactions together off-chain, then submitting a single transaction to the Ethereum mainnet as a “commitment”.

The commitment contains a summary of the transactions in the rollup, along with cryptographic proof that verifies the validity of the transactions.

Here is a step-by-step overview of how Optimistic Rollups work:

  1. Multiple transactions are grouped together into a bundle by the rollup operator. These transactions are not executed on the Ethereum mainnet but instead are processed off-chain.
  2. The rollup operator generates a commitment, which is a single transaction that summarizes the transactions in the bundle. The commitment includes cryptographic proof that verifies the validity of the transactions.
  3. The commitment is submitted to the Ethereum mainnet, where it is included in a block. The block timestamp is recorded as the “roll-up submission timestamp”.
  4. Validators and watchers on the mainnet are incentivized to monitor the rollup and challenge any invalid transactions. If a fraudulent transaction is identified, a challenge can be submitted to the Ethereum mainnet, which triggers a dispute resolution process.
  5. If no challenges are submitted during a predefined “challenge period”, the roll-up submission is considered “finalized”. At this point, the state of the Ethereum network is updated to reflect the state changes that occurred in the rollup.
  6. If a challenge is submitted and validated, the rollup operator is penalized, and the transaction is reverted.
  7. Any user who wants to interact with the rollup can do so by submitting a transaction to the rollup operator. This transaction is processed off-chain, and the resulting state changes are then included in the next rollup submission to the mainnet.

Optimistic Rollups provide a scalable and cost-effective solution for processing transactions on the Ethereum network while maintaining the security and decentralization of the blockchain.

However, they do rely on a dispute resolution process that requires active participation from validators and watchers to maintain the integrity of the rollup.

Benefits of Optimistic Rollups

Optimistic Rollups offer several benefits for the Ethereum ecosystem, including:

  1. Scalability: Optimistic Rollups allow for a high degree of scalability by processing multiple transactions off-chain and submitting them to the Ethereum mainnet as a single transaction.
  2. Cost-effectiveness: Since transactions in Optimistic Rollups are processed off-chain, they are much cheaper than on-chain transactions, reducing the cost of gas fees for users.
  3. Security: While not as secure as zkRollups, Optimistic Rollups still provide a high degree of security through the use of fraud proofs. This ensures that transactions on the rollup are valid and have not been tampered with.
  4. Decentralization: Optimistic Rollups are designed to be decentralized, meaning that no single entity has control over the network. This ensures that the network is resistant to censorship and collusion, and maintains the trustless nature of the Ethereum ecosystem.

Optimistic Rollups offer a promising solution for scaling the Ethereum network, while maintaining the core principles of security, decentralization, and cost-effectiveness.

Differences between zkRollups and Optimistic Rollups

zkRollups and Optimistic Rollups are both Layer 2 scaling solutions for Ethereum, but they use different mechanisms to achieve scalability and transaction throughput. Here are the key differences between zkRollups and Optimistic Rollups:

  • Verification mechanism: zkRollups use zero-knowledge proofs to verify the validity of transactions, while Optimistic Rollups use fraud proofs. This means that zkRollups can provide a higher level of security and privacy than Optimistic Rollups, but they require more computational resources to generate the zero-knowledge proofs.
  • Transaction finality: zkRollups provide instant finality for transactions, meaning that once a transaction is included in a rollup block, it cannot be challenged or reversed. In contrast, Optimistic Rollups rely on a dispute resolution process, which can take several hours to resolve. This means that zkRollups are better suited for use cases that require fast and secure settlement, such as cryptocurrency exchanges or high-frequency trading.
  • User experience: Optimistic Rollups offer a better user experience than zkRollups since transactions on Optimistic Rollups do not require a waiting period for verification. However, the wait time for dispute resolution can be a disadvantage of Optimistic Rollups if a user needs to wait for several hours to have their transaction confirmed.
  • Gas cost: Optimistic Rollups generally have lower gas costs than zkRollups, since they do not require as many computational resources to generate zero-knowledge proofs. This makes Optimistic Rollups more cost-effective for smaller transactions.

Overall, both zkRollups and Optimistic Rollups offer promising solutions for scaling the Ethereum network, but they have different trade-offs in terms of security, transaction finality, user experience, and gas cost. The choice between these two solutions will depend on the specific use case and requirements of the application.

Also Read: How Zkrollups & Optimistic Rollups Can Reduce Gas Fees on Ethereum

Which is better for scaling Ethereum?  

While both zkRollups and Optimistic Rollups provide considerable benefits for expanding the Ethereum network, there is no obvious victor.

The decision between the two is determined by the individual requirements of each dApp. zkRollups may be a preferable solution for dApps that demand a high level of security and privacy.

Optimistic Rollups may be a preferable solution for dApps that demand greater flexibility and the ability to handle more sophisticated smart contracts off-chain.

Both zkRollups and Optimistic Rollups aim to boost the scalability of the Ethereum network and create a more efficient and cost-effective platform for dApps to run on.

As the need for decentralized apps grows, it is probable that zkRollups and Optimistic Rollups will play a key part in the Ethereum ecosystem’s future.

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