Thanks for the info. > you could "sponsor yourself" directly or through a cycle involving > 1 txn.
Ah I see, because the sighash flags aren't used to create the TXID. I don't really see the problem with cycles tho. Could a cycle cause problems for anyone? Seems like it would be a harmless waste of bytes. The fee-sponsoring OP_VER looks good too tho. On Wed, Jan 19, 2022 at 2:08 PM Jeremy <jlru...@mit.edu> wrote: > SIGHASH_BUNDLE > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-April/015862.html > > By cycles I meant that if you commit to the sponsors by TXID from the > witness, you could "sponsor yourself" directly or through a cycle involving > > 1 txn. > > With OP_VER I was talking about the proposal I linked here > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-September/018168.html > which used OP_VER to indicate a txn sponsoring txn. Because the OP_VER is > in the output space, and uses TXIDs, it is cycle-free. > > > -- > @JeremyRubin <https://twitter.com/JeremyRubin> > <https://twitter.com/JeremyRubin> > > > On Wed, Jan 19, 2022 at 8:52 AM Billy Tetrud <billy.tet...@gmail.com> > wrote: > >> Hmm, I don't know anything about SIGHASH_BUNDLE. The only references >> online I can find are just mentions (mostly from you). What is >> SIGHASH_BUNDLE? >> >> > unless you're binding a WTXID >> >> That could work, but it would exclude cases where you have a transaction >> that has already been partially signed and someone wants to, say, only sign >> that transaction if some 3rd party signs a transaction paying part of the >> fee for it. Kind of a niche use case, but it would be nice to support it if >> possible. If the transaction hasn't been signed at all yet, a new >> transaction can just be created that includes the prospective fee-payer, >> and if the transaction is fully signed then it has a WTXID to use. >> >> > then you can have fee bumping cycles >> >> What kind of cycles do you mean? You're saying these cycles would make it >> less robust to reorgs? >> >> > OP_VER >> >> I assume you mean something other than pushing the version onto the stack >> <https://bitcoin.stackexchange.com/questions/97258/given-op-ver-was-never-used-is-disabled-and-not-considered-useful-can-its-meani>? >> Is that related to your fee account idea? >> >> >> On Wed, Jan 19, 2022 at 1:32 AM Jeremy <jlru...@mit.edu> wrote: >> >>> Ah my bad i misread what you were saying as being about SIGHASH_BUNDLE >>> like proposals. >>> >>> For what you're discussing, I previously proposed >>> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-September/018168.html >>> which is similar. >>> >>> The benefit of the OP_VER output is that SIGHASH_EXTERNAL has the issue >>> that unless you're binding a WTXID (which is maybe too specific?) then you >>> can have fee bumping cycles. Doing OP_VER output w/ TXID guarantees that >>> you are acyclic. >>> >>> The difference between a fee account and this approach basically boils >>> down to the impact on e.g. reorg stability, where the deposit/withdraw >>> mechanism is a bit more "robust" for reorderings in reorgs than the in-band >>> transaction approach, although they are very similar. >>> >>> -- >>> @JeremyRubin <https://twitter.com/JeremyRubin> >>> <https://twitter.com/JeremyRubin> >>> >>> >>> On Tue, Jan 18, 2022 at 8:53 PM Billy Tetrud <billy.tet...@gmail.com> >>> wrote: >>> >>>> > because you make transactions third party malleable it becomes >>>> possible to bundle and unbundle transactions. >>>> >>>> What I was suggesting doesn't make it possible to malleate someone >>>> else's transaction. I guess maybe my proposal of using a sighash flag >>>> might have been unclear. Imagine it as a script opcode that just says "this >>>> transaction must be mined with this other transaction" - the only >>>> difference being that you can use any output with any encumberance as an >>>> input for fee bumping. It doesn't prevent the original transaction from >>>> being mined on its own. So adding junk inputs would be no more of a problem >>>> than dust attacks already are. It would be used exactly like cpfp, except >>>> it doesn't spend the parent. >>>> >>>> I don't think what I was suggesting is as different from your proposal. >>>> All the problems of fee revenue optimization and feerate rules that you >>>> mentioned seem like they'd also exist for your proposal, or for cpfp. Let >>>> me know if I should clarify further. >>>> >>>> On Tue, Jan 18, 2022 at 8:51 PM Jeremy <jlru...@mit.edu> wrote: >>>> >>>>> The issue with sighash flags is that because you make transactions >>>>> third party malleable it becomes possible to bundle and unbundle >>>>> transactions. >>>>> >>>>> This means there are circumstances where an attacker could e.g. see >>>>> your txn, and then add a lot of junk change/inputs + 25 descendants and >>>>> strongly anchor your transaction to the bottom of the mempool. >>>>> >>>>> because of rbf rules requiring more fee and feerate, this means you >>>>> have to bump across the whole package and that can get really messy. >>>>> >>>>> more generally speaking, you could imagine a future where mempools >>>>> track many alternative things that might want to be in a transaction. >>>>> >>>>> suppose there are N inputs each with a weight and an amount of fee >>>>> being added and the sighash flags let me pick any subset of them. However, >>>>> for a txn to be standard it must be < 100k bytes and for it to be >>>>> consensus >>>>> < 1mb. Now it is possible you have to solve a knapsack problem in order to >>>>> rationally bundle this transaction out of all possibilities. >>>>> >>>>> This problem can get even thornier, suppose that the inputs I'm adding >>>>> themselves are the outputs of another txn in the mempool, now i have to >>>>> track and propagate the feerates of that child back up to the parent txn >>>>> and track all these dependencies. >>>>> >>>>> perhaps with very careful engineering these issues can be tamed. >>>>> however it seems with sponsors or fee accounts, by separating the pays-for >>>>> from the participates-in concerns we can greatly simplify it to something >>>>> like: compute effective feerate for a txn, including all sponsors that pay >>>>> more than the feerate of the base txn. Mine that txn and it's subsidies >>>>> using the normal algo. If you run out of space, all subsidies are >>>>> same-sized so just take the ones that pay the highest amount up until the >>>>> added marginal feerate is less than the next eligible txn. >>>>> >>>>> >>>>> -- >>>>> @JeremyRubin <https://twitter.com/JeremyRubin> >>>>> <https://twitter.com/JeremyRubin> >>>>> >>>>> >>>>> On Tue, Jan 18, 2022 at 6:38 PM Billy Tetrud <billy.tet...@gmail.com> >>>>> wrote: >>>>> >>>>>> 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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