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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