I see, its not primarily to make it cheaper to append fees, but also allows appending fees in cases that aren't possible now. Is that right? I can certainly see the benefit of a more general way to add a fee to any transaction, regardless of whether you're related to that transaction or not.
How would you compare the pros and cons of your account-based approach to something like a new sighash flag? Eg a sighash flag that says "I'm signing this transaction, but the signature is only valid if mined in the same block as transaction X (or maybe transactions LIST)". This could be named SIGHASH_EXTERNAL. Doing this would be a lot more similar to other bitcoin transactions, and no special account would need to be created. Any transaction could specify this. At least that's the first thought I would have in designing a way to arbitrarily bump fees. Have you compared your solution to something more familiar like that? On Tue, Jan 18, 2022 at 11:43 AM Jeremy <jlru...@mit.edu> wrote: > Can you clarify what you mean by "improve the situation"? > > There's a potential mild bytes savings, but the bigger deal is that the > API should be much less vulnerable to pinning issues, fix dust leakage for > eltoo like protocols, and just generally allow protocol designs to be fully > abstracted from paying fees. You can't easily mathematically quantify API > improvements like that. > -- > @JeremyRubin <https://twitter.com/JeremyRubin> > <https://twitter.com/JeremyRubin> > > > On Tue, Jan 18, 2022 at 8:13 AM Billy Tetrud <billy.tet...@gmail.com> > wrote: > >> Do you have any back-of-the-napkin math on quantifying how much this >> would improve the situation vs existing methods (eg cpfp)? >> >> >> >> On Sat, Jan 1, 2022 at 2:04 PM Jeremy via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> Happy new years devs, >>> >>> I figured I would share some thoughts for conceptual review that have >>> been bouncing around my head as an opportunity to clean up the fee paying >>> semantics in bitcoin "for good". The design space is very wide on the >>> approach I'll share, so below is just a sketch of how it could work which >>> I'm sure could be improved greatly. >>> >>> Transaction fees are an integral part of bitcoin. >>> >>> However, due to quirks of Bitcoin's transaction design, fees are a part >>> of the transactions that they occur in. >>> >>> While this works in a "Bitcoin 1.0" world, where all transactions are >>> simple on-chain transfers, real world use of Bitcoin requires support for >>> things like Fee Bumping stuck transactions, DoS resistant Payment Channels, >>> and other long lived Smart Contracts that can't predict future fee rates. >>> Having the fees paid in band makes writing these contracts much more >>> difficult as you can't merely express the logic you want for the >>> transaction, but also the fees. >>> >>> Previously, I proposed a special type of transaction called a "Sponsor" >>> which has some special consensus + mempool rules to allow arbitrarily >>> appending fees to a transaction to bump it up in the mempool. >>> >>> As an alternative, we could establish an account system in Bitcoin as an >>> "extension block". >>> >>> *Here's how it might work:* >>> >>> 1. Define a special anyone can spend output type that is a "fee account" >>> (e.g. segwit V2). Such outputs have a redeeming key and an amount >>> associated with them, but are overall anyone can spend. >>> 2. All deposits to these outputs get stored in a separate UTXO database >>> for fee accounts >>> 3. Fee accounts can sign only two kinds of transaction: A: a fee amount >>> and a TXID (or Outpoint?); B: a withdraw amount, a fee, and an address >>> 4. These transactions are committed in an extension block merkle tree. >>> While the actual signature must cover the TXID/Outpoint, the committed data >>> need only cover the index in the block of the transaction. The public key >>> for account lookup can be recovered from the message + signature. >>> 5. In any block, any of the fee account deposits can be: released into >>> fees if there is a corresponding tx; consolidated together to reduce the >>> number of utxos (this can be just an OP_TRUE no metadata needed); or >>> released into fees *and paid back* into the requested withdrawal key >>> (encumbering a 100 block timeout). Signatures must be unique in a block. >>> 6. Mempool logic is updated to allow attaching of account fee spends to >>> transactions, the mempool can restrict that an account is not allowed more >>> spend more than it's balance. >>> >>> *But aren't accounts "bad"?* >>> >>> Yes, accounts are bad. But these accounts are not bad, because any funds >>> withdrawn from the fee extension are fundamentally locked for 100 blocks as >>> a coinbase output, so there should be no issues with any series of reorgs. >>> Further, since there is no "rich state" for these accounts, the state >>> updates can always be applied in a conflict-free way in any order. >>> >>> >>> *Improving the privacy of this design:* >>> >>> This design could likely be modified to implement something like >>> Tornado.cash or something else so that the fee account paying can be >>> unlinked from the transaction being paid for, improving privacy at the >>> expense of being a bit more expensive. >>> >>> Other operations could be added to allow a trustless mixing to be done >>> by miners automatically where groups of accounts with similar values are >>> trustlessly split into a common denominator and change, and keys are >>> derived via a verifiable stealth address like protocol (so fee balances can >>> be discovered by tracing the updates posted). These updates could also be >>> produced by individuals rather than miners, and miners could simply honor >>> them with better privacy. While a miner generating an update would be able >>> to deanonymize their mixes, if you have your account mixed several times by >>> independent miners that could potentially add sufficient privacy. >>> >>> The LN can also be used with PTLCs to, in theory, have another >>> individual paid to sponsor a transaction on your behalf only if they reveal >>> a valid sig from their fee paying account, although under this model it's >>> hard to ensure that the owner doesn't pay a fee and then 'cancel' by >>> withdrawing the rest. However, this could be partly solved by using >>> reputable fee accounts (reputation could be measured somewhat >>> decentralized-ly by longevity of the account and transactions paid for >>> historically). >>> >>> *Scalability* >>> >>> This design is fundamentally 'decent' for scalability because adding >>> fees to a transaction does not require adding inputs or outputs and does >>> not require tracking substantial amounts of new state. >>> >>> Paying someone else to pay for you via the LN also helps make this more >>> efficient if the withdrawal issues can be fixed. >>> >>> *Lightning:* >>> >>> This type of design works really well for channels because the addition >>> of fees to e.g. a channel state does not require any sort of pre-planning >>> (e.g. anchors) or transaction flexibility (SIGHASH flags). This sort of >>> design is naturally immune to pinning issues since you could offer to pay a >>> fee for any TXID and the number of fee adding offers does not need to be >>> restricted in the same way the descendant transactions would need to be. >>> >>> *Without a fork?* >>> >>> This type of design could be done as a federated network that bribes >>> miners -- potentially even retroactively after a block is formed. That >>> might be sufficient to prove the concept works before a consensus upgrade >>> is deployed, but such an approach does mean there is a centralizing layer >>> interfering with normal mining. >>> >>> >>> Happy new year!! >>> >>> Jeremy >>> >>> -- >>> @JeremyRubin <https://twitter.com/JeremyRubin> >>> <https://twitter.com/JeremyRubin> >>> _______________________________________________ >>> bitcoin-dev mailing list >>> bitcoin-dev@lists.linuxfoundation.org >>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >>> >>
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