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

Background and motivation of EIP-7732

Since the problem of MEV is difficult to solve from the root cause, taking fair competition measures is the only way to avoid security risks. After the merger of Ethereum, in order to maintain fairness and reduce the scale effect of large pledge pools on MEV extraction, Flashbots launched MEV-Boost, which uses the PBS (Proposer-Builder Separation) mechanism to reduce the opportunities for validators to directly participate in MEV activities and convert MEV Stakeholder diversity. At present, 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 assigned an official EIP number: EIP-7732. EIP-7732 is a change to the consensus layer without requiring changes to 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.

EIP-7732 is proposed, in addition to solving the problem of verifiers relying on third parties (such as MEV-Boost) to build execution payloads, it also aims to optimize the efficiency in the verification process. Current validators must complete all consensus and perform 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 computational burden of a single node, but also increases the possibility of errors. By separating execution verification and consensus verification, it is ensured that nodes only need to complete relatively few tasks within the critical 4-second window, thereby reducing the computational 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 of the validator. Anyone who has enough funds to stake on the beacon chain and has the ability Any validator who performs block construction tasks can become a builder. The builder is responsible for building and submitting promises for execution of the payload. Validators can now outsource the execution of payloads to builders, while focusing more on consensus-level tasks.

Execution Payload is the core part of the block and contains all transaction and status 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 list and state transition results. By removing this field, the creation and verification of execution content is separated from the creation and verification of the beacon block. As an alternative, EIP-7732 introduces a new data structure, SignedExecutionPayloadHeader, which includes the builder's promise of an execution payload that will be revealed in the future.

Overall process

Builder’s tasks: The builder is responsible for creating the execution payload and generating a promise that will expose the execution payload. The promise is encapsulated in a SignedExecutionPayloadHeader data structure, which includes a hash of the execution payload and a digital signature of this hash to ensure the immutability of the data and verification of origin. This promise indicates that the builder will expose the complete execution payload at some determined time in the future and specifies an amount to be paid to the beacon block proposer to incentivize the beacon block proposer to include this promise.

The tasks of the beacon block proposer: The beacon block proposer (validator) cooperates with the builder and does not need to directly handle the execution details of the transaction when creating a new beacon block, but includes the commitment provided by the builder , and then broadcast the entire beacon block to the Ethereum network to reach consensus. Including only commitments reduces the burden on the network and speeds up the propagation of beacon blocks and the consensus verification process. After the builder's commitment is processed, the tip in the commitment is deducted from the builder's beacon chain balance and credited to the beacon block proposer. After a beacon block proposer successfully broadcasts a beacon block with a commitment, the builder is required to expose the complete execution payload within a specified time window.

PTC Verification: To monitor whether builders publicly execute payloads in a timely manner, a group of validators randomly selected by the Beacon Chain network form the Payload Timeliness Committee (PTC). The PTC is responsible for checking whether the builder has exposed an execution payload that matches the promise within the specified time window. If the builder fails to disclose in a timely and correct manner, PTC will broadcast a negative outcome and the builder will face a penalty of staking reduction. If the PTC verification passes, the full verification of the execution payload is deferred to be processed separately during the next beacon block, that is, deferred verification.

In addition, the proposal also introduces regulatory rules and a new penalty mechanism for PTC to ensure the rigor and fairness of the entire verification process. At the same time, due to the separation of execution payloads and beacon blocks, 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.

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