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Blockchain Security

What Is Linea, the New zk-Rollup Developed by Consensys?


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Rob Behnke

October 18th, 2023


Linea is a zk-Rollup developed by Consensys. It is hosted on the Ethereum blockchain and is designed to enable further development on Ethereum by addressing the scalability constraints of the Ethereum platform.

What is a Zero-Knowledge (ZK) Rollup?

One of the most frequently cited limitations of the Ethereum platform is its limited scalability and transaction volume. On average, Ethereum can only process about 20-30 transactions per second. This limited throughput presents a significant limitation to the future growth of the Ethereum-based smart contract ecosystem.

Zero-knowledge rollups (ZK-rollups) are designed to enhance the scalability of Ethereum — and other blockchains — by moving transactions off-chain. By reducing the amount of data each transaction records on-chain, ZK-rollups enable blockchains to handle higher transaction volumes.

ZK-rollups balance the need for scalability and security through the use of zero-knowledge proofs (ZKPs). A ZKP can prove that something is true without revealing the thing being proven. ZKPs are designed so that anyone can validate the proof and verify its correctness.

In the case of ZK-rollups, ZKPs are used to verify that a set of transactions is valid without revealing the transaction data. 

A ZK-rollup prover will:

  1. Collect a batch of transactions.

  2. Calculate the effect that they have on the state of the ZK-rollup platform.

  3. Generate a ZKP demonstrating that the set of transactions generated the resulting state update.

  4. Submit the updated state and ZKP to the on-chain verifier contract.

The verifier will validate the ZKP, and, if it’s correct, adopt the updated state.

The end result of this is that only the ZKP and updated state are stored on-chain. Since this is smaller than the whole batch of transactions, the ZK-rollup increases the transaction volume that Ethereum can handle.

How Does Linea Work?

Linea is an Ethereum ZK-rollup designed to support developers on Ethereum. It is a fully EVM-compatible Layer-2 (L2) protocol that runs as a ZK-rollup.

The fact that Linea implements a fully EVM-compatible ZK-rollup is significant because it dramatically enhances developers’ abilities to build on top of Ethereum. Without full EVM compatibility, development on a ZK-rollup is limited because some operations may not be implemented.

Since Linea uses Consensys’ zkEVM, developers can write the same code for the Linea L2 as they would for Ethereum’s L1. This means that existing smart contracts implemented on L1 could be easily ported to the rollup — increasing their scalability — and the rollup supports developers writing contracts specifically for its L2.

Benefits of Linea

Linea is an Ethereum L2 ZK-rollup designed by Consensys, a major player in the space. Linea was carefully designed and implemented to provide a number of benefits for developers and for the Ethereum network.

Scalability

Like all Ethereum rollups, one of the biggest benefits that Linea offers is increased scalability for the Ethereum blockchain. By processing transaction data off-chain and only storing the ZKPs and state data on-chain, it dramatically reduces the amount of on-chain storage used by each transaction. As a result, a greater number of transactions can be fit into each Ethereum block, enhancing the scalability of the blockchain.

Linea also implements conflation, in which it attempts to combine multiple rollup blocks into a single L1 state update if they come close enough together and room is available. This helps to further decrease the amount of space on the blockchain used by transactions.

Reduced Execution Cost

Another benefit of Linea’s reduction of on-chain data and execution is reduced gas fees. Gas fees are charged for instructions executed within the L1 EVM. By moving transactions to an L2 EVM and recording only the state updates on the L1, Linea reduces not only the L1 data usage but also the transactions performed by the L1, resulting in cheaper transactions.

Security

Linea is an example of a ZK-rollup, which uses ZKPs to validate state updates that are performed by transactions recorded off-chain. By storing state updates and ZKPs on-chain instead of the entire set of transactions that produced that update, Linea reduces the data stored on-chain with no loss of security.

In contrast, an Optimistic Rollup — the other type of rollup — doesn’t use ZKPs to prove the validity of transactions performed off-chain. Instead, it publishes a batch of transactions that have been rolled up, and these transactions are finalized after a challenge period. If someone can find an error in the transactions and submits a challenge within the challenge period, then a transaction is rejected.

A ZK-rollup like Linea is more secure than an Optimistic Rollup because the proof of a batch’s legitimacy is provided alongside it as a ZKP. Optimistic Rollups, on the other hand, rely on someone generating and submitting a challenge in time for an invalid batch, making them vulnerable to Denial of Service (DoS) attacks and other threats.

Instant Finality

Another advantage of Linea and other ZK-rollups is that they offer instant finality for transactions. Once a batch of transactions is posted to L1, they are finalized and can be used in other transactions.

In contrast, Optimistic Rollups have a challenge period. Only after a rollup transaction has made it through this period without being challenged are they considered final.

Quantum Resistance

Linea uses lattice-based cryptography as the basis for its zero-knowledge proofs. Unlike many types of asymmetric cryptography used by blockchain solutions, lattice-based cryptography is believed to be resistant to attacks by quantum computers. This means that the Linea ZK-rollup will not require an upgrade to quantum-resistant cryptography in the event that quantum computers large enough to threaten classical cryptographic algorithms become available.

Conclusion

Linea is designed to enhance the scalability of the Ethereum blockchain. A ZK-rollup with full EVM compatibility provides the ability to run smart contracts designed for the Ethereum environment without storing full data on-chain.

At the same time, Linea has also been designed and implemented with a focus on security. As a ZK-rollup, it lacks the security concerns of Optimistic Rollups, relying on ZKPs to prove the validity of rollup transactions rather than crypto-economics to inspire challenges. Additionally, Linea has demonstrated a forward-thinking approach to security, as demonstrated by its use of post-quantum algorithms for implementing its ZKPs.