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

Author: Maggie@Foresight Ventures

1. Background

In 2020, Ethereum released “Rollup Centered Ethereum Roadmap", 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 , serving 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,Ethereum 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.

2. How will 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.

L2 transaction submission: When the Rollup is submitted, the Blob-carrying transaction is used to store the Rollup data in the Blob. The payload of the Blob-carrying transaction is rlp([tx_payload_body, blobs, commitments, proofs]), where

tx_payload_body< /strong> - 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 KZG commitments. 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 the dispute point is submitted 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 Blob data will be deleted after about 18 days, the challenge period must be before it is deleted, which is satisfied by current optimistic rollups. Generally, the challenge period does not exceed 7 days.

ZK Rollups adapt to EIP4844

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



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

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 packaged. . 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 EIP4844’s blob commitment is BLS12-381, while the ETH precompiled contract only supports BN254. Due to the different curves, it is difficult for us to Verify blob commitment completion proof directly in the smart contract.

ZkEVM/zkVM using SNARK needs to solve the problem mentioned in point 2 that ZK proof cannot be generated due to curve mismatch.

Waiting for Ethereum to support BLS12-381 precompiled contracts. This will be long.

Use another proof method 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.

4. Which L2s are adapted to EIP4844?

Optimistic rollup is relatively easy to adapt to EIP4844.

Arbitrum will launch the Arb OS20 upgrade on March 14 to implement the EIP changes of the Cancun upgrade(article link). Arbitrum belongs to Stage 1 Rollup. Both transaction submission and fraud proof need to adapt to EIP4844, and its security is relatively good.

Optimism launched the Ecotone upgrade to complete the adaptation on March 14th(article link). 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. After the adaptation is completed, all super chain networks in the Op ecosystem will also benefit from EIP-4844.

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).

zkSync has been upgraded through Boojum to allow zkSync to complete the transition from SNARK to STARK proof. This is also preparation for the EIP4844 upgrade. Boojun is a proof system based on STARK.

It is relatively complicated to adapt using SNARK's rollup

Polygon zkEVM is expected to be launched with Feijoa upgrade in May, adapting to EIP-4844. (Article link)

Scroll published an article last year introducing the idea of ​​adapting EIP4844 (Article link).

The most impressive thing is Morph, who is an Optimistic ZK Rollup and was the first to release the zkSNARK zkEVM adaptation plan for EIP4844 ,It can be said to be the first to complete the rollup of zkSNARK zkEVM of EIP4844 (article link). 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 have doubts about 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.