EIP-3521: Reduce access list cost

Simple Summary

Reduce the cost of declaring tx.to storage keys in access lists.

Motivation

Currently, a transaction must read at least 25 distinct storage slots in tx.to before it’s more expensive to forego an access list.

ACCESS_LIST_ADDRESS_COST + (ACCESS_LIST_STORAGE_KEY_COST + WARM_STORAGE_READ_COST) * x = COLD_SLOAD_COST * x
x = 24

EIP-2930 requires the address under which the storage keys reside be declared explicitly, since it must be added to the EIP-2929 accessed_addresses list. However, tx.to is a special case that is added by default, so paying ACCESS_LIST_ADDRESS_COST for tx.to is essentially paying twice for the same address. Avoiding overpayment here will reduce the differential to just 5 unique reads before using an access list is cheaper – making them a more attractive option.

Specification

Treat the first occurrence of tx.to in an access list as calldata for gas accounting purposes. Do not charge ACCESS_LIST_ADDRESS_COST for it. Storage keys underneath the address are unaffected.

If tx.to == nil, tx.to is defined be the derived contract address created by the transaction.

Rationale

Why charge at all?

EIP-2930 is specifically written to make access lists simple to reason about and validate. It may be possible to modify the structure of the access list to avoid including tx.to explicitly, but this would renege on the spirit of EIP-2930.

Why charge as calldata?

The cost of calldata was thoroughly analyzed in EIP-2028 to determine a fair value that is not susceptible to denial-of-service attacks. We consider this the lower bound on how much transaction data should cost. Since there is no computation burden imposed for adding tx.to to the accessed_addresses map (it’s added by default by EIP-2929), there is no reason to charge more than the absolute minimum for the data.

Test Cases

{
    "0xffffffffffffffffffffffffffffffffffffffff": []
}
cost = 320

{
    "0x00ffffffffffffffffffffffffffffffffffffff": []
}
cost = 308

{
    "0xffffffffffffffffffffffffffffffffffffffff": []
    "0xffffffffffffffffffffffffffffffffffffffff": []
}
cost = 2720

{
    "0xffffffffffffffffffffffffffffffffffffffff": [
        "0x00"
    ]
    "0xffffffffffffffffffffffffffffffffffffffff": []
}
cost = 4620

{
    "0xffffffffffffffffffffffffffffffffffffffff": [
        "0x00"
    ]
    "0xffffffffffffffffffffffffffffffffffffffff": [
        "0x00"
    ]
}
cost = 6520

Backwards Compatibility

No issues.

Security Considerations

None.

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Matt Garnett, "EIP-3521: Reduce access list cost," Ethereum Improvement Proposals, no. 3521, April 2021. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-3521.