Blockchain scalability is a critical issue that has been a subject of extensive research and development. One of the promising solutions to this problem is the concept of rollups, a Layer 2 scaling solution that executes transactions off-chain and posts the data on-chain. This post provides a comprehensive analysis of classic rollups, including Optimistic Rollups and ZK Rollups, Enshrined Rollups, and Sovereign Rollups, focusing on their detailed information, advantages, disadvantages, and a comparative study among them.

Classic Rollups: An Overview

Classic rollups, including Optimistic Rollups and ZK Rollups, are Layer 2 solutions that aim to increase the transaction throughput of a blockchain by executing transactions off-chain and posting the data on-chain. They rely on the security of the underlying Layer 1 blockchain (like Ethereum) for data availability and order of transactions, while the computation is performed off-chain. This approach allows for a significant increase in the number of transactions processed per second, while maintaining the security and decentralization properties of the underlying blockchain.

Optimistic Rollups

Optimistic Rollups are a type of Layer 2 construction on Ethereum that allows for the execution of smart contracts off-chain while still maintaining a high level of security provided by the Ethereum mainnet. They operate under the assumption that all transactions are correct (hence the term 'optimistic') and only run full computation in the event of a dispute.

In an Optimistic Rollup, transactions are executed off-chain in a replicated virtual machine, which maintains a similar state to the Ethereum mainnet. The state transitions are recorded and submitted to the Ethereum mainnet as 'rollup blocks'. These blocks are not immediately accepted as valid; instead, they are subject to a challenge period during which any observer can 'challenge' the validity of a block by providing a proof that the block includes an invalid transaction.

Pros:

1. Scalability: Optimistic Rollups can handle around 100-200 transactions per second (TPS), a significant improvement over Ethereum's 15 TPS.

2. Compatibility: They are fully compatible with Ethereum, allowing for the execution of complex smart contracts.

3. Security: They inherit the security of the underlying Layer 1 blockchain.

Cons:

1. Data latency: In the event of a dispute, it can take up to one week for the challenge period to resolve, leading to potential delays.

2. Complexity: Implementing Optimistic Rollups can be complex due to the need for fraud proofs.

ZK Rollups

ZK Rollups are another type of Layer 2 solution that bundle multiple inputs and outputs into a single transaction, using zero-knowledge proofs to verify the validity of transactions. Unlike Optimistic Rollups, ZK Rollups do not require a challenge period as they provide instant finality.

In a ZK Rollup, transactions are grouped together and a single 'proof' is generated and verified by the Ethereum mainnet. This proof attests to the validity of all transactions in the group, ensuring that only valid state transitions are included in the Ethereum mainnet. The use of zero-knowledge proofs allows for the compression of multiple transactions into a single proof, significantly reducing the amount of data that needs to be stored on-chain.

Pros:

1. Scalability: ZK Rollups can process thousands of transactions per second, offering even greater scalability than Optimistic Rollups.

2. Instant finality: Transactions are instantly finalized, avoiding the delay associated with the challenge period in Optimistic Rollups.

3. Security: Like Optimistic Rollups, they also inherit the security of the underlying Layer 1 blockchain.

Cons: 

1. Limited functionality: ZK Rollups currently support a limited set of operations and are not fully compatible with Ethereum's smart contracts.

2. Complexity: The technology behind ZK Rollups, particularly zero-knowledge proofs, is complex and requires specialized knowledge to implement.

Comparison between Optimistic Rollups and ZK Rollups

While both Optimistic Rollups and ZK Rollups aim to increase the scalability of Ethereum, they do so in different ways and have distinct trade-offs.

1. Scalability: ZK Rollups offer higher scalability than Optimistic Rollups due to the use of zero-knowledge proofs, which allow for the compression of multiple transactions into a single proof.

2. Finality: ZK Rollups provide instant finality, while Optimistic Rollups have a delay due to the challenge period.

3. Compatibility: Optimistic Rollups are fully compatible with Ethereum's smart contracts, while ZK Rollups currently support a limited set of operations.

4. Complexity: Both solutions are complex, but ZK Rollups are particularly so due to the use of zero-knowledge proofs.

Enshrined Rollups

Enshrined Rollups are a type of rollup that enjoys some sort of consensus integration at Layer 1 (L1). They contrast with smart contract rollups, which live fully at Layer 2 (L2), outside of consensus. Consensus integration can endow enshrined rollups with superpowers at the cost of significant tradeoffs.

The term "enshrined" refers to the fact that the rollup's logic is embedded (or "enshrined") into the protocol of the Layer 1 blockchain itself. This means that the rollup's operation is governed by the consensus rules of the Layer 1 blockchain, rather than being determined by a separate set of rules or a smart contract.

Pros:

Scalability: By performing computations off-chain and only posting the results to the blockchain, enshrined rollups can significantly increase the number of transactions that a blockchain can process per second.

Security: Because the rollup's operation is governed by the Layer 1 blockchain's consensus rules, enshrined rollups inherit the security properties of the Layer 1 blockchain. This means that as long as the Layer 1 blockchain is secure, the enshrined rollup is also secure.

Cons:

Complexity: Enshrined rollups add a layer of complexity to the blockchain system. This can make them more difficult to understand and implement, potentially slowing down their adoption.

Sovereign Rollups

Sovereign Rollups are a newer concept that combines elements of Layer 1 blockchains and rollups. Like classic rollups, they execute transactions off-chain and post the data on-chain. However, unlike classic rollups, they handle their own settlement and do not rely on the security of the underlying Layer 1 blockchain for transaction verification.

In a Sovereign Rollup, transactions are published to another blockchain (typically for ordering and data availability), but the nodes of the Sovereign Rollup are responsible for verifying the transactions. This approach allows Sovereign Rollups to have a degree of independence (or 'sovereignty') from the underlying Layer 1 blockchain.

Pros:

1. Independence: Sovereign Rollups have their own consensus and can operate independently of the underlying Layer 1 blockchain.

2. Flexibility: They can define their own rules for transaction verification and settlement.

Cons:

1. Security: Since Sovereign Rollups handle their own settlement, they do not inherit the security of the underlying Layer 1 blockchain.

2. Complexity: Implementing a Sovereign Rollup can be complex due to the need for a separate consensus mechanism.

Comparison between Classic Rollups, Enshrined Rollups, and Sovereign Rollups

The main difference between classic rollups, enshrined rollups, and Sovereign Rollups lies in where transactions are verified and settled.

Verification: In classic rollups, transactions are verified by the underlying Layer 1 blockchain, while in enshrined rollups, the rollup's operation is governed by the consensus rules of the Layer 1 blockchain. In Sovereign Rollups, transactions are verified by the nodes of the Sovereign Rollup.

Settlement: Classic rollups and enshrined rollups rely on the underlying Layer 1 blockchain for settlement, while Sovereign Rollups handle their own settlement.

Security: Classic rollups and enshrined rollups inherit the security of the underlying Layer 1 blockchain, while Sovereign Rollups do not.

Independence: Sovereign Rollups can operate independently of the underlying Layer 1 blockchain, while classic rollups and enshrined rollups cannot.

Complexity: All solutions are complex, but enshrined rollups add an extra layer of complexity due to their integration with the Layer 1 blockchain's consensus rules.

Conclusion

Rollups, both classic, enshrined, and sovereign, present promising solutions to the scalability issues faced by Layer 1 blockchains. While classic rollups, including Optimistic Rollups and ZK Rollups, offer significant improvements in transaction throughput and security, they are not without their trade-offs, including complexity and, in the case of Optimistic Rollups, potential delays due to the challenge period. Enshrined rollups, while offering similar benefits, add an extra layer of complexity due to their integration with the Layer 1 blockchain's consensus rules. On the other hand, Sovereign Rollups offer a degree of independence and flexibility not seen in classic or enshrined rollups, but they do not inherit the security of the underlying Layer 1 blockchain. As research and development in this area continue, it will be interesting to see how these technologies evolve and how they will shape the future of blockchain scalability.