Optimize EOA EXTCODEHASH

Abstract

This proposal is an optimization for EIP-1052, For addresses with a balance, but without code, the codehash should still be 0x.

When an address add.code == 0x and add.balance != 0, add.codehash==0 is required instead of add.codehash==keccak256("")

Motivation

EIP-1052 was proposed to save gas fees. However, due to some flaws in the set specifications, in actual applications, due to safety concerns, they will not actually be used. In order for EIP-1052 to be truly useful, it should be optimized.

If someone uses it based on the proposal of EIP-1052 and does not notice the change when add.balance != 0, there may be security issues.

Specification

The behaviour of EXTCODEHASH is changed in the following way:

1. When calling EXTCODEHASH, the codehash of the address with balance but no code is still 0x

Rationale

EIP-1052 In order to include the function of BALANCE, let the EXTCODEHASH of the address without balance be 0x, and the EXTCODEHASH of the address with balance be keccak256("").

The contract address can be calculated in advance. Whether it is CREATE or CREATE2, it is possible that the contract is not created but has a balance. For security, You can actually only use keccak256(add.code) == keccak256("") or add.code.length ==0 instead of add.codehash == 0,, which makes the original intention of EIP-1052 meaningless.

For example, uniswap V2 uses stored addresses to determine whether a contract exists. If this EXTCODEHASH is optimized, can save a huge amount of gas.

If someone uses a add.codehash==0 to determine whether a contract has been created, due to intuition and the lack of details in many documents, they will not think that the codehash of an address with a balance will change from 0x to keccak256(""). If someone maliciously attacks at this time, it will cause some bad effects.

Backwards Compatibility

Using codehash to determine whether a non-contract address has a balance will not be available

Reference Implementation

Code reference for execution-specs

After modification

def extcodehash(evm: Evm) -> None:
    address = to_address(pop(evm.stack))
    charge_gas(evm, GAS_CODE_HASH)
    account = get_account(evm.env.state, address)
    if account == EMPTY_ACCOUNT:
        codehash = U256(0)
    else:
	codehash = U256.from_be_bytes(keccak256(account.code))
	if codehash == U256(hexstr="c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470"):
	    codehash = U256(0)
    push(evm.stack, codehash)
    evm.pc += 1

Source code

def extcodehash(evm: Evm) -> None:
    address = to_address(pop(evm.stack))
    charge_gas(evm, GAS_CODE_HASH)
    account = get_account(evm.env.state, address)
    if account == EMPTY_ACCOUNT:
        codehash = U256(0)
    else:
        codehash = U256.from_be_bytes(keccak256(account.code))

    push(evm.stack, codehash)
    evm.pc += 1

Security Considerations

Using codehash to determine whether a non-contract address has a balance will not be available

Copyright

Copyright and related rights waived via CC0.