SLOT precompile

Abstract

This EIP proposes to add a new precompile that returns the corresponding slot number for the current block.

Motivation

It is currently possible to calculate the slot number from the block timestamp. However, this requires hardcoding the chain slot length into a smart contract. This would require the contract code to be changed in the event of a future change to slot length. A better approach is for the slot length to be abstracted away from applications, and instead the slot number can be calculated in the consensus layer client and exposed in a precompile.

Example application: Encrypted Mempools

An example of a smart contract that needs the slot number is a validation contract for an encrypted mempool. In order to be secure, the validity of encrypted mempool transactions should be tied to the inclusion of all transactions by a proposer in the correct slot. This rule can be enforced by a smart contract using this precompile.

Specification

If block.timestamp >= TBD a new precompiled contract SLOT shall be created at address TBD.

SLOT returns as output the current slot number as an 8 byte ulong in big endian encoding.

Gas Cost

The gas cost for SLOT is a fixed fee of 2.

RPC changes

The slot number is calculated in the consensus layer and passed to the execution layer through the engine API.

newPayload change

The engine_newPayload endpoint shall include a new parameter slot_number of type uint64.

PayloadAttributes change

The engine API's PayloadAttributes object shall be extended to include a slot_number field of type uint64.

New JSON-RPC endpoints

Consensus layer clients may implement the following new RPC endpoints to convert between slot numbers and their corresponding timestamps.

eth_getSlotNumberFromTimestamp: uint64 -> uint64 eth_getTimestampFromSlotNumber: uint64 -> uint64

Rationale

Gas Price

The precompile is priced to match similar opcodes in the W_base set.

Precompile

Making the feature a precompile rather than an opcode gives L2s flexibility to decide whether to implement it.

Calculation in consensus layer

The slot number could alternatively be calculated in the execution layer using the timestamp, but it is more appropriate to calculate values pertaining to the beacon chain in the consensus layer. Additionally this avoids code duplication, as the slot number is already calculated in the consensus layer.

Backwards Compatibility

No backward compatibility issues found.

Test Cases

N/A

Security Considerations

None.

Copyright

Copyright and related rights waived via CC0.