The Cancun upgrade is coming. Which L2s have been adapted?

Author: Maggie@Foresight Ventures

TL;DR:

• The Cancun upgrade will be launched on March 13, 2024, and EIP4844 will be online soon. Danksharding is the core of the Ethereum roadmap, and this upgrade is the first step to realize Danksharding.

• Ethereum  After L2 adapts to EIP4844, transaction fees have dropped significantly, and L2's TPS has doubled. Users will feel that transactions are faster, cheaper, experience smoother, and more responsive. There will be more complex and larger Dapp applications on these L2s.

• Optimistic rollups are easier to adapt to EIP4844, while ZK rollups are more complex to adapt. Ethereum does not have a precompiled contract to support BLS12-381 elliptic curves, which makes it difficult to verify some ZKPs and hinders the progress of ZK rollups adapting to EIP4844.

• The problem of elliptic curves can be solved in two ways, 1. Wait for Ethereum to respond to BLS12- 381 elliptic curve for pre-compilation; 2. Use another proof method to achieve the same purpose, use BN254 supported by Ethereum pre-compilation.

• Currently,Arbitrum, Optimistic, Starknet, zkSync, Scroll, Polygon zkEVM and the new L2 Morph are all adapting to EIP4844. Among them, Arbitrum, Optimistic and Starknet stated that they will implement EIP4844 adaptation after the Cancun upgrade. Morph took the lead in releasing the innovative zkSNARK zkEVM adaptation solution, which will be the first zkSNARK zkEVM adapted to EIP4844

1. Background

In 2020, Ethereum released the "Ethereum route centered on Rollup Figure", as well as the final picture of Ethereum described in "Endgame" published by Vitalik the following year, determined the general direction of Ethereum: optimizing the construction of Ethereum's base layer to serve Rollup.

Ethereum designed Danksharding's sharding technology to improve the usability of Ethereum as a data availability layer. It will significantly reduce L2’s transaction fees, increase Rollup’s TPS, and achieve a substantial expansion of Ethereum

Until this year, theEthereum Cancun-Dencun upgrade finally Launched on March 13, 2024, EIP4844 is about to go online. This hard fork can be said to be the first step for Ethereum to implement Danksharding and is the core of the Ethereum roadmap.

For more information about what is the DA layer, the technical principles of Danksharding, and the content of EIP4844, please Refer to a technical article I wrote last year: DA (Data Availability) Summer is coming? https://foresightnews.pro/article/detail/33575

2. How does the Cancun upgrade benefit L2?

EIP4844 introduces a new transaction type called blob-carrying transaction. Each blob-carrying transaction can "carry" a list of blobs. A blob is a packet of data, approximately 125 KB. Blobs are stored for a short period of time, only 4096 epochs, which is a little more than 18 days.

1. L2 transaction fees have dropped significantly. Because Blobs do not require permanent storage, Blobs are larger and cheaper than block space. Blobs can store 10 times more data than Calldata at the same gas consumption. Rollup adapted to EIP4844 can store transaction data in Blobs, reducing transaction fees by an order of magnitude.

2. The TPS of L2 is doubled. The current target is 3 blobs per block, with a maximum of 6 blobs allowed. Blocks are only 90KB, and each blob is about 125KB. The introduction of Blob is equivalent to expanding the space several times of the block to store Rollup data, so the TPS of Rollup can also be doubled. And "On Increasing the Block Gas Limit" written by Toni and Vitalic stated that by increasing the block Gas limit and the price of non-zero Calldata bytes, a smaller block size with fewer variables will be achieved, so that more can be added in the future. Blob. The more blobs, the greater the storage space.

For end users, Ethereum   After L2 adapts to EIP4844, transactions will be faster and more cost-effective. Low, the experience is smoother and more responsive. There will be more complex and larger Dapp applications on these L2s.

3. How does L2 adapt to EIP4844?

How does L2 adapt to EIP4844? We need to discuss Optimistic Rollup and ZK Rollup separately.

Optimistic Rollups adapt to EIP4844

Optimistic rollup is passed Fraud proof is used to ensure the correctness of rollup execution. That is, the node first chooses to believe that the state transition is correct. Unless someone initiates a fraud certificate within a specified period of time to prove that the previously submitted state transition is illegal, the state transition will be revoked.

Optimistic Rollup is simpler to adapt to EIP4844 than ZK rollup. Submit all L2 transactions to L1 through Blob-carrying transactions to complete the adaptation. In addition, the fraud proof needs to be adjusted to adapt to EIP4844. This part can be done slowly. After all, many optimistic rollups have not yet launched fraud proofs. I put a fraud certificate online, but found that no fraud certificate had been submitted for more than two years.

1. L2 transaction submission: When submitting Rollup, use Blob -Carrying transactions, storing Rollup data in Blobs. The payload of the Blob-carrying transaction is rlp([tx_payload_body, blobs, commitments, proofs]), where

• tx_payload_body - is the TransactionPayloadBody of the standard EIP-2718 blob transaction.

• blobs  - List of blobs. A transaction can contain up to two blobs.

• commitments - Blob's KZG commitment list.

• proofs - Blob and a list of proofs corresponding to the KZG commitment. This proof will be verified by the ETH node.

• Adjust fraud proof:

• First, the prover and the challenger need multiple rounds of interaction to find the dispute point.

• Then submit the disputed point to L1 for judgment. To adapt to EIP4844, it may be necessary to prove that the data at issue is stored on a certain Blob.

• Since the Blob data will be deleted after about 18 days, the challenge period must be before it is deleted. This is the current optimistic rollups. Be satisfied. Generally, the challenge period does not exceed 7 days.

ZK Rollups adapts to EIP4844

ZK rollup uses ZKP to prove that the L2 state transition is correct. ZK rollup adaptation to EIP4844 is more complicated than optimistic rollup.



1.L2 transaction submission: This step of Optimistic Rollup is similar.

2. ZK proof submission: Compared with the ZK Rollup before adaptation, in addition to the ZKP proof of state transition, one more proof process is required. That is to say, it is proved that the blob commitment and the transaction batch are corresponding, thus ensuring that the input of the state transition proof is correct.

For example: the ZK circuit of state transition can generate a proof of the calculation process a + a = b. The ZKP generated when (a=1,b=2) and (a=2,b=4) is legal. Therefore, I also need to provide a proof that the input I provided at that time was (a=1,b=2) instead of (a=2,b=4).

This does not need to be done before adapting to EIP4844, because the data is directly stored in Calldata and can be read directly, ensuring that the input will not be adjusted. After using EIP4844, the Blob data cannot be read directly, and this can only be proven through a new circuit.

It is easier to implement this proof mechanism using STARK's ZK rollup (such as Starknet). This is a challenge for ZK rollup using SNARK. The reason is:The elliptic curve used by the blob commitment of EIP4844 is BLS12-381, while the precompiled contract of ETH only supports BN254. Due to the different curves, it is difficult for us to Verify blob commitment completion proof directly in the smart contract.

1. ZkEVM/zkVM using SNARK needs to solve the problem mentioned in point 2 The problem of not being able to generate ZK proof due to curve mismatch.
   

• Waiting Ethereum supports BLS12-381 precompiled contracts. This will be long.

• Use another method of proof to prove. To design new circuits, you must use the BN254 elliptic curve supported by the precompiled contract. Currently, we see Morph taking this approach. This also makes Morph the first zkEVM to complete EIP4844 adaptation.

For Morph’s EIP-4844 zkEVM integrated solution, please see: https://medium.com /@morphlayer2/morphs-solution-to-eip-4844-zkevm-integration-7f469910478f

4. Which L2s are adapted to EIP4844?

In the Optimistic rollup, Optimism and Arbitrum have expressed their commitment to adopting EIP-4844 and are working closely with their communities to test and deploy the necessary updates. Arbitrum is a Stage 1 rollup and has relatively good security. It involves the need to adapt fraud proof to EIP4844. Optimistic rollup is a Stage 0 rollup. There is currently no fraud proof. It is easier to adapt, but the security is not high enough.

In ZK rollup, the difficulty of rollup adaptation using STRAK and SNARK is different. It is easier to adapt EIP4844 with STARK's rollup, and Starknet is one of the representatives. Starknet published an article stating that Cancun will implement EIP4844 adaptation after the upgrade (article link). With SNARK rollup, zkSync is also exploring how to leverage blob-carrying transactions to further reduce costs and improve performance. Scroll published an article last year introducing the idea of ​​adapting to EIP4844 (article link)

The most impressive thing is Morph, which is an Optimistic ZK Rollup and was the first to release zkEVM's solution to adapt EIP4844It can be said to be the first zkEVM  Rollup to complete EIP4844.

Optimistic ZK Rollup combines the advantages of both types of Rollup. It optimistically believes in the execution results submitted by Sequencer and allows those who doubt the results to initiate challenges. Only when a challenge is issued, the prover will generate ZKP to prove the correctness of the execution results. It has the efficiency of Optimistic rollup and the ZK-proven reliability of ZK rollup.