Hi Peter, If feerate-dependent timelocks (FDTs) (1) are supported, it would be possible to use CTV to define a transaction with a fixed fee and no anchor outputs, as long as it's racing against a transaction with an FDT.
Regards, John (1) https://lists.linuxfoundation.org/pipermail/lightning-dev/2023-December/004254.html Sent with Proton Mail secure email. On Wednesday, January 24th, 2024 at 11:31 AM, Peter Todd via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote: > CheckTemplateVerify(1) is a proposed covenant opcode that commits to the > transaction that can spend an output. Namely, # of inputs, # of outputs, > outputs hash, etc. In practice, in many if not most CTV use-cases intended to > allow multiple parties to share a single UTXO, it is difficult to impossible > to > allow for sufficient CTV variants to cover all possible fee-rates. It is > expected that CTV would be usually used with anchor outputs to pay fees; by > creating an input of the correct size in a separate transaction and including > it in the CTV-committed transaction; or possibly, via a transaction sponsor > soft-fork. > > This poses a scalability problem: to be genuinely self-sovereign in a protocol > with reactive security, such as Lightning, you must be able to get > transactions > mined within certain deadlines. To do that, you must pay fees. All of the > intended exogenous fee-payment mechanisms for CTV require users to have at > least one UTXO of suitable size to pay for those fees. > > This requirement for all users to have a UTXO to pay fees negates the > efficiency of CTV-using UTXO sharing schemes, as in an effort to share a UTXO, > CTV requires each user to have an extra UTXO. The only realistic alternative > is > to use a third party to pay for the UTXO, eg via a LN payment, but at that > point it would be more efficient to pay an out-of-band mining fee. That of > course is highly undesirable from a mining centralization perspective.(2) > > Recommendations: CTV in its current form be abandoned as design foot-gun. > Other > convenant schemes should be designed to work well with replace-by-fee, to > avoid > requirements for extra UTXOs, and to maximize on-chain efficiency. > > 1) > https://github.com/bitcoin/bips/blob/deae64bfd31f6938253c05392aa355bf6d7e7605/bip-0119.mediawiki > 2) > https://petertodd.org/2023/v3-transactions-review#anchor-outputs-are-a-danger-to-mining-decentralization > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
