How does EIP-7732 (ePBS) optimize the block verification process?

Author: 0XNATALIE Source: chainfeeds

Background and motivation of EIP-7732

Since the problem of MEV is difficult to solve from the root, taking fair competition measures is the only way to avoid security risks. After the Ethereum merger, in order to maintain fairness and reduce the scale effect of large staking pools on MEV extraction, Flashbots launched MEV-Boost, which adopts the PBS (Proposer-Builder Separation) mechanism to reduce the opportunities for validators to directly participate in MEV activities and diversify MEV stakeholders. Currently, the proportion of MEV-Boost blocks has exceeded 90%.

With the widespread adoption of MEV-Boost, the Ethereum community began to worry about the security risks that may arise from relying on this third-party service. Therefore, the idea of ​​implementing PBS within the Ethereum protocol was born, called ePBS (Enshrined Proposer-Builder Separation). Recently, ePBS was given an official EIP number: EIP-7732. EIP-7732 is a change to the consensus layer, without changing the execution layer. The core is to logically and temporally separate execution verification from consensus verification, and postpone execution verification until consensus verification is completed.

In addition to solving the problem of validators relying on third parties (such as MEV-Boost) to build execution payloads, the proposal of EIP-7732 also aims to optimize the efficiency of the verification process. Currently, validators must complete all consensus and execution state transition functions in a very short time (within 4 seconds), which places extremely high demands on computing resources and network bandwidth. During this window period, validators need to verify and confirm a large amount of transaction information and update the status of the blockchain, which not only increases the computing burden of a single node, but also increases the possibility of errors. By separating execution verification and consensus verification, it is ensured that within the critical 4-second window, nodes only need to complete relatively few tasks, thereby reducing the computing burden and speeding up network propagation.

The core content of EIP-7732

EIP-7732 creates a new role "Builder", which is a new optional responsibility for validators. Any validator with sufficient funds to stake on the beacon chain and the ability to perform block building tasks can become a builder. The builder is responsible for building and submitting commitments to execute payloads. Validators can now outsource the construction of execution payloads to builders, and focus more on consensus-level tasks.

The execution payload is the core part of the block, containing all transactions and state change information. The process of building an execution payload includes selecting transactions from the memory pool, sorting transactions, executing transactions in sequence, and packaging all information to form an execution payload.

To achieve this separation, EIP-7732 removes the ExecutionPayload field, which contains all data related to transaction execution, such as transaction lists and state transition results. By removing this field, the creation and verification of execution content is separated from the creation and verification of beacon blocks. Instead, EIP-7732 introduces a new data structure SignedExecutionPayloadHeader, which includes the builder's commitment to the execution payload to be revealed in the future.

Overall process

The builder's tasks: The builder is responsible for creating the execution payload and generating a commitment to publicly execute the payload. The commitment is encapsulated in the SignedExecutionPayloadHeader  data structure, which includes the hash of the execution payload and the digital signature of the hash to ensure the immutability of the data and the verification of the source. This commitment indicates that the builder will disclose the full execution payload at a certain time in the future, and specifies the amount to be paid to the beacon block proposer to incentivize the beacon block proposer to include this commitment.

Beacon block proposer's tasks: Beacon block proposers (validators) work with builders to create new beacon blocks without directly processing the execution details of transactions, but instead include the commitment provided by the builder, and then broadcast the entire beacon block to the Ethereum network to reach consensus. Including only commitments can reduce the burden on the network and speed up the propagation of beacon blocks and the consensus verification process. After processing the builder's commitment, the tip in the commitment will be deducted from the builder's beacon chain balance and credited to the beacon block proposer. After the beacon block proposer successfully broadcasts the beacon block containing the commitment, the builder needs to disclose the full execution payload within the specified time window.

PTC Verification:In order to monitor whether the builder publicly executes the payload in a timely manner, a group of validators randomly selected by the beacon chain network forms the Payload Timeliness Committee (PTC). PTC is responsible for checking whether the builder has publicly executed the payload that matches the commitment within the specified time window. If the builder fails to disclose it in a timely and correct manner, PTC will broadcast a negative result, and the builder will face a penalty of slashing the stake. If the PTC verification is passed, the full verification of the execution payload is postponed to the next beacon block period for separate processing, that is, delayed verification.

In addition, the proposal also introduces regulatory rules and new penalty mechanisms for PTC to ensure the strictness and fairness of the entire verification process. At the same time, due to the separation of the execution payload and the beacon block, the fork selection logic has also been adjusted to adapt to the new verification process. These changes are expected to significantly improve the security and efficiency of the network. Through a series of designs, EIP-7732 improves Ethereum's processing efficiency and reduces network latency.