Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
After getting neutral to negative feedback on the choice, I have switched to OP_TRUE on the BIP and implementation. Cheers, Greg On Sat, Feb 4, 2023 at 11:03 AM Peter Todd wrote: > On Fri, Feb 03, 2023 at 09:07:29PM -0500, Greg Sanders wrote: > > I'm not particularly persuaded, but also not wedded to either idea. > > > > Fixed up tests for the OP_TRUE case here: > > https://github.com/instagibbs/bitcoin/tree/ephemeral-anchors-true > > Thanks. > > Looking through that, I think a lot of those test cases don't actually > need to > be changed to OP_2, as they aren't trying to test anything related to > standardness. > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
On Fri, Feb 03, 2023 at 09:07:29PM -0500, Greg Sanders wrote: > I'm not particularly persuaded, but also not wedded to either idea. > > Fixed up tests for the OP_TRUE case here: > https://github.com/instagibbs/bitcoin/tree/ephemeral-anchors-true Thanks. Looking through that, I think a lot of those test cases don't actually need to be changed to OP_2, as they aren't trying to test anything related to standardness. -- https://petertodd.org 'peter'[:-1]@petertodd.org signature.asc Description: PGP signature ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
I'm not particularly persuaded, but also not wedded to either idea. Fixed up tests for the OP_TRUE case here: https://github.com/instagibbs/bitcoin/tree/ephemeral-anchors-true On Fri, Feb 3, 2023 at 5:10 PM Peter Todd wrote: > On Thu, Feb 02, 2023 at 03:47:28PM -0500, Greg Sanders wrote: > > > OP_TRUE is the obvious way to do this, and it results with a 1 on the > > stack, > > which plays better with other standardness rules. > > > > What other standardness rules? MINAMALIF? How does that interact with the > > proposal? > > It makes sense to require scripts to leave just a single OP_TRUE on the > stack > at the end of execution, as otherwise that can be a source of malleability > in > certain circumstances where the scriptSig ends up providing the OP_TRUE. I > don't believe we actually implement this as a rule right now. But you could > easily imagine that happening in a future upgrade. > > Leaving an OP_2 on the stack doesn't achieve that and would require a > special-cased workaround. Spending the time now to do the obvious thing - > use > OP_TRUE as the canonical anyone-can-spend output - avoids this issue. > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
On Thu, Feb 02, 2023 at 03:47:28PM -0500, Greg Sanders wrote: > > OP_TRUE is the obvious way to do this, and it results with a 1 on the > stack, > which plays better with other standardness rules. > > What other standardness rules? MINAMALIF? How does that interact with the > proposal? It makes sense to require scripts to leave just a single OP_TRUE on the stack at the end of execution, as otherwise that can be a source of malleability in certain circumstances where the scriptSig ends up providing the OP_TRUE. I don't believe we actually implement this as a rule right now. But you could easily imagine that happening in a future upgrade. Leaving an OP_2 on the stack doesn't achieve that and would require a special-cased workaround. Spending the time now to do the obvious thing - use OP_TRUE as the canonical anyone-can-spend output - avoids this issue. -- https://petertodd.org 'peter'[:-1]@petertodd.org signature.asc Description: PGP signature ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
> OP_TRUE is the obvious way to do this, and it results with a 1 on the stack, which plays better with other standardness rules. What other standardness rules? MINAMALIF? How does that interact with the proposal? On Thu, Feb 2, 2023 at 3:22 PM Peter Todd wrote: > On Thu, Feb 02, 2023 at 01:36:24PM -0500, Greg Sanders wrote: > > Quickly checked, it fails a number of standardness tests in > unit/functional > > tests in Bitcoin Core, at least. > > > > OP_2 was actually Luke Jr's idea circa 2017 for about the same reasons, I > > just independently arrived at the same conclusion. > > Well, frankly I really don't like the idea of using OP_2 just to avoid > changing > some unit tests. We're doing something that many people will use for years > to > come, that's unnecessarily obscure just because we don't want to spend a > bit of > some modifying some tests to pass. > > OP_TRUE is the obvious way to do this, and it results with a 1 on the > stack, > which plays better with other standardness rules. OP_2 means we *also* may > need > to special case having a 2 on the stack in certain implementations of other > standardness rules. > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
On Thu, Feb 02, 2023 at 01:36:24PM -0500, Greg Sanders wrote: > Quickly checked, it fails a number of standardness tests in unit/functional > tests in Bitcoin Core, at least. > > OP_2 was actually Luke Jr's idea circa 2017 for about the same reasons, I > just independently arrived at the same conclusion. Well, frankly I really don't like the idea of using OP_2 just to avoid changing some unit tests. We're doing something that many people will use for years to come, that's unnecessarily obscure just because we don't want to spend a bit of some modifying some tests to pass. OP_TRUE is the obvious way to do this, and it results with a 1 on the stack, which plays better with other standardness rules. OP_2 means we *also* may need to special case having a 2 on the stack in certain implementations of other standardness rules. -- https://petertodd.org 'peter'[:-1]@petertodd.org signature.asc Description: PGP signature ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Quickly checked, it fails a number of standardness tests in unit/functional tests in Bitcoin Core, at least. OP_2 was actually Luke Jr's idea circa 2017 for about the same reasons, I just independently arrived at the same conclusion. On Thu, Feb 2, 2023 at 10:06 AM Peter Todd wrote: > On Thu, Feb 02, 2023 at 09:59:09AM -0500, Greg Sanders wrote: > > Hi Peter, > > > > For the most principled of reasons: > > > > Because I have to change test vectors everywhere! > > Specifically, you mean you'd have to change tests that test something is > non-standard? > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
On Thu, Feb 02, 2023 at 09:59:09AM -0500, Greg Sanders wrote: > Hi Peter, > > For the most principled of reasons: > > Because I have to change test vectors everywhere! Specifically, you mean you'd have to change tests that test something is non-standard? -- https://petertodd.org 'peter'[:-1]@petertodd.org signature.asc Description: PGP signature ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Hi Peter, For the most principled of reasons: Because I have to change test vectors everywhere! Greg On Thu, Feb 2, 2023 at 9:52 AM Peter Todd wrote: > On Fri, Jan 27, 2023 at 09:05:20AM -0500, Greg Sanders via bitcoin-dev > wrote: > > Hello again dev, > > > > Due to the interest in the proposal and the prodding of certain folks, > I've > > written up a short draft BIP of the Ephemeral Anchors idea here: > > > https://github.com/instagibbs/bips/blob/ephemeral_anchor/bip-ephemeralanchors.mediawiki > > > > The pull request at https://github.com/bitcoin/bitcoin/pull/26403 has > been > > refreshed on top of the latest V3 proposal, but the BIP itself is > > unaffected. > > The BIP states that: > > Why OP_2 not OP_TRUE? OP_TRUE is often used in test vectors, using > OP_2 has > the same benefits and none of these common collisions. > > Why is a "collision" harmful in this case? > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
On Fri, Jan 27, 2023 at 09:05:20AM -0500, Greg Sanders via bitcoin-dev wrote: > Hello again dev, > > Due to the interest in the proposal and the prodding of certain folks, I've > written up a short draft BIP of the Ephemeral Anchors idea here: > https://github.com/instagibbs/bips/blob/ephemeral_anchor/bip-ephemeralanchors.mediawiki > > The pull request at https://github.com/bitcoin/bitcoin/pull/26403 has been > refreshed on top of the latest V3 proposal, but the BIP itself is > unaffected. The BIP states that: Why OP_2 not OP_TRUE? OP_TRUE is often used in test vectors, using OP_2 has the same benefits and none of these common collisions. Why is a "collision" harmful in this case? -- https://petertodd.org 'peter'[:-1]@petertodd.org signature.asc Description: PGP signature ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Hello again dev, Due to the interest in the proposal and the prodding of certain folks, I've written up a short draft BIP of the Ephemeral Anchors idea here: https://github.com/instagibbs/bips/blob/ephemeral_anchor/bip-ephemeralanchors.mediawiki The pull request at https://github.com/bitcoin/bitcoin/pull/26403 has been refreshed on top of the latest V3 proposal, but the BIP itself is unaffected. Cheers, Greg On Wed, Nov 30, 2022 at 10:32 AM Greg Sanders wrote: > Small update. > > A bit ago I went ahead and implemented ephemeral anchors on top of the V3 > proposal to see what the complexity looks like: > https://github.com/bitcoin/bitcoin/pull/26403 > > Roughly 130 loc excluding tests, using OP_2 instead of OP_TRUE to not camp > the value that is used elsewhere. > > Please let me know if you have any early feedback on this! > > Greg > > On Thu, Oct 20, 2022 at 9:42 AM Greg Sanders wrote: > >> So it doesn't look like I'm ignoring a good question: >> >> No solid noninteractive ideas, unless we get some very flexible sighash >> softfork. Interactively, I think you can get collaborative fee bumps under >> the current consensus regime and ephemeral anchors. The child will just be >> built with inputs from different people. >> >> On Wed, Oct 19, 2022 at 11:12 AM James O'Beirne >> wrote: >> >>> I'm also very happy to see this proposal, since it gets us closer to >>> having a mechanism that allows the contribution to feerate in an >>> "unauthenticated" way, which seems to be a very helpful feature for vaults >>> and other contracting protocols. >>> >>> One possible advantage of the sponsors interface -- and I'm curious for >>> your input here Greg -- is that with sponsors, assuming we relaxed the "one >>> sponsor per sponsoree" constraint, multiple uncoordinated parties can >>> collaboratively bump a tx's feerate. A simple example would be a batch >>> withdrawal from an exchange could be created with a low feerate, and then >>> multiple users with a vested interest of expedited confirmation could all >>> "chip in" to raise the feerate with multiple sponsor transactions. >>> >>> Having a single ephemeral output seems to create a situation where a >>> single UTXO has to shoulder the burden of CPFPing a package. Is there some >>> way we could (possibly later) amend the ephemeral anchor interface to allow >>> for this kind of collaborative sponsoring? Could you maybe see "chained" >>> ephemeral anchors that would allow this? >>> >>> >>> On Tue, Oct 18, 2022 at 12:52 PM Jeremy Rubin via bitcoin-dev < >>> bitcoin-dev@lists.linuxfoundation.org> wrote: >>> Excellent proposal and I agree it does capture much of the spirit of sponsors w.r.t. how they might be used for V3 protocols. The only drawbacks I see is they don't work for lower tx version contracts, so there's still something to be desired there, and that the requirement to sweep the output must be incentive compatible for the miner, or else they won't enforce it (pass the buck onto the future bitcoiners). The Ephemeral UTXO concept can be a consensus rule (see https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate UTXO") we add later on in lieu of managing them by incentive, so maybe it's a cleanup one can punt. One question I have is if V3 is designed for lightning, and this is designed for lightning, is there any sense in requiring these outputs for v3? That might help with e.g. anonymity set, as well as potentially keep the v3 surface smaller. On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > > does that effectively mark output B as unspendable once the child > gets confirmed? > > Not at all. It's a normal spend like before, since the parent has been > confirmed. It's completely unrestricted, not being bound to any > V3/ephemeral anchor restrictions on size, version, etc. > > On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> Hi Greg, >> >> Thank you very much for sharing your proposal! >> >> I think there's one thing about the second part of your proposal that >> I'm missing. Specifically, assuming the scenario of a v3 transaction with >> three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child >> transaction spends A and OP_TRUE, does that effectively mark output B as >> unspendable once the child gets confirmed? If so, isn't the implication >> therefore that to safely spend a transaction with an ephemeral anchor, >> all >> outputs must be spent? Thanks! >> >> Best, >> Arik >> >> On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: >> >> Hello Everyone, >> >> Following up on the "V3 Transaction" discussion here >>
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Small update. A bit ago I went ahead and implemented ephemeral anchors on top of the V3 proposal to see what the complexity looks like: https://github.com/bitcoin/bitcoin/pull/26403 Roughly 130 loc excluding tests, using OP_2 instead of OP_TRUE to not camp the value that is used elsewhere. Please let me know if you have any early feedback on this! Greg On Thu, Oct 20, 2022 at 9:42 AM Greg Sanders wrote: > So it doesn't look like I'm ignoring a good question: > > No solid noninteractive ideas, unless we get some very flexible sighash > softfork. Interactively, I think you can get collaborative fee bumps under > the current consensus regime and ephemeral anchors. The child will just be > built with inputs from different people. > > On Wed, Oct 19, 2022 at 11:12 AM James O'Beirne > wrote: > >> I'm also very happy to see this proposal, since it gets us closer to >> having a mechanism that allows the contribution to feerate in an >> "unauthenticated" way, which seems to be a very helpful feature for vaults >> and other contracting protocols. >> >> One possible advantage of the sponsors interface -- and I'm curious for >> your input here Greg -- is that with sponsors, assuming we relaxed the "one >> sponsor per sponsoree" constraint, multiple uncoordinated parties can >> collaboratively bump a tx's feerate. A simple example would be a batch >> withdrawal from an exchange could be created with a low feerate, and then >> multiple users with a vested interest of expedited confirmation could all >> "chip in" to raise the feerate with multiple sponsor transactions. >> >> Having a single ephemeral output seems to create a situation where a >> single UTXO has to shoulder the burden of CPFPing a package. Is there some >> way we could (possibly later) amend the ephemeral anchor interface to allow >> for this kind of collaborative sponsoring? Could you maybe see "chained" >> ephemeral anchors that would allow this? >> >> >> On Tue, Oct 18, 2022 at 12:52 PM Jeremy Rubin via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> Excellent proposal and I agree it does capture much of the spirit of >>> sponsors w.r.t. how they might be used for V3 protocols. >>> >>> The only drawbacks I see is they don't work for lower tx version >>> contracts, so there's still something to be desired there, and that the >>> requirement to sweep the output must be incentive compatible for the miner, >>> or else they won't enforce it (pass the buck onto the future bitcoiners). >>> The Ephemeral UTXO concept can be a consensus rule (see >>> https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate >>> UTXO") we add later on in lieu of managing them by incentive, so maybe it's >>> a cleanup one can punt. >>> >>> One question I have is if V3 is designed for lightning, and this is >>> designed for lightning, is there any sense in requiring these outputs for >>> v3? That might help with e.g. anonymity set, as well as potentially keep >>> the v3 surface smaller. >>> >>> On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < >>> bitcoin-dev@lists.linuxfoundation.org> wrote: >>> > does that effectively mark output B as unspendable once the child gets confirmed? Not at all. It's a normal spend like before, since the parent has been confirmed. It's completely unrestricted, not being bound to any V3/ephemeral anchor restrictions on size, version, etc. On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > Hi Greg, > > Thank you very much for sharing your proposal! > > I think there's one thing about the second part of your proposal that > I'm missing. Specifically, assuming the scenario of a v3 transaction with > three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child > transaction spends A and OP_TRUE, does that effectively mark output B as > unspendable once the child gets confirmed? If so, isn't the implication > therefore that to safely spend a transaction with an ephemeral anchor, all > outputs must be spent? Thanks! > > Best, > Arik > > On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: > > Hello Everyone, > > Following up on the "V3 Transaction" discussion here > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html > , I would like to elaborate a bit further on some potential follow-on work > that would make pinning severely constrained in many setups]. > > V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks > under some constraints[0]. This means that when a replacement is to be > made > and propagated, it costs the expected amount of fees to do so. This is a > great start. What's left in this subset of pinning is *package limit* > pinning. In other words, a fee-paying transaction cannot enter the mempool
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Hi, Greg. I find this proposal super interesting, and IIUC something that seems fairly "safe" to allow (assuming V3). For LN having the commitment transaction pay a non-zero fee is a cause for a lot of complexity in the channel state machine. Something like this would remove a lot of edge cases and add more flexibility around adding HTLCs. Thanks! - Johan On Thu, Oct 20, 2022 at 3:42 PM Greg Sanders via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > So it doesn't look like I'm ignoring a good question: > > No solid noninteractive ideas, unless we get some very flexible sighash > softfork. Interactively, I think you can get collaborative fee bumps under > the current consensus regime and ephemeral anchors. The child will just be > built with inputs from different people. > > On Wed, Oct 19, 2022 at 11:12 AM James O'Beirne > wrote: > >> I'm also very happy to see this proposal, since it gets us closer to >> having a mechanism that allows the contribution to feerate in an >> "unauthenticated" way, which seems to be a very helpful feature for vaults >> and other contracting protocols. >> >> One possible advantage of the sponsors interface -- and I'm curious for >> your input here Greg -- is that with sponsors, assuming we relaxed the "one >> sponsor per sponsoree" constraint, multiple uncoordinated parties can >> collaboratively bump a tx's feerate. A simple example would be a batch >> withdrawal from an exchange could be created with a low feerate, and then >> multiple users with a vested interest of expedited confirmation could all >> "chip in" to raise the feerate with multiple sponsor transactions. >> >> Having a single ephemeral output seems to create a situation where a >> single UTXO has to shoulder the burden of CPFPing a package. Is there some >> way we could (possibly later) amend the ephemeral anchor interface to allow >> for this kind of collaborative sponsoring? Could you maybe see "chained" >> ephemeral anchors that would allow this? >> >> >> On Tue, Oct 18, 2022 at 12:52 PM Jeremy Rubin via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> Excellent proposal and I agree it does capture much of the spirit of >>> sponsors w.r.t. how they might be used for V3 protocols. >>> >>> The only drawbacks I see is they don't work for lower tx version >>> contracts, so there's still something to be desired there, and that the >>> requirement to sweep the output must be incentive compatible for the miner, >>> or else they won't enforce it (pass the buck onto the future bitcoiners). >>> The Ephemeral UTXO concept can be a consensus rule (see >>> https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate >>> UTXO") we add later on in lieu of managing them by incentive, so maybe it's >>> a cleanup one can punt. >>> >>> One question I have is if V3 is designed for lightning, and this is >>> designed for lightning, is there any sense in requiring these outputs for >>> v3? That might help with e.g. anonymity set, as well as potentially keep >>> the v3 surface smaller. >>> >>> On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < >>> bitcoin-dev@lists.linuxfoundation.org> wrote: >>> > does that effectively mark output B as unspendable once the child gets confirmed? Not at all. It's a normal spend like before, since the parent has been confirmed. It's completely unrestricted, not being bound to any V3/ephemeral anchor restrictions on size, version, etc. On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > Hi Greg, > > Thank you very much for sharing your proposal! > > I think there's one thing about the second part of your proposal that > I'm missing. Specifically, assuming the scenario of a v3 transaction with > three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child > transaction spends A and OP_TRUE, does that effectively mark output B as > unspendable once the child gets confirmed? If so, isn't the implication > therefore that to safely spend a transaction with an ephemeral anchor, all > outputs must be spent? Thanks! > > Best, > Arik > > On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: > > Hello Everyone, > > Following up on the "V3 Transaction" discussion here > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html > , I would like to elaborate a bit further on some potential follow-on work > that would make pinning severely constrained in many setups]. > > V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks > under some constraints[0]. This means that when a replacement is to be > made > and propagated, it costs the expected amount of fees to do so. This is a > great start. What's left in this subset of pinning is *package limit* > pinning. In other
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
So it doesn't look like I'm ignoring a good question: No solid noninteractive ideas, unless we get some very flexible sighash softfork. Interactively, I think you can get collaborative fee bumps under the current consensus regime and ephemeral anchors. The child will just be built with inputs from different people. On Wed, Oct 19, 2022 at 11:12 AM James O'Beirne wrote: > I'm also very happy to see this proposal, since it gets us closer to > having a mechanism that allows the contribution to feerate in an > "unauthenticated" way, which seems to be a very helpful feature for vaults > and other contracting protocols. > > One possible advantage of the sponsors interface -- and I'm curious for > your input here Greg -- is that with sponsors, assuming we relaxed the "one > sponsor per sponsoree" constraint, multiple uncoordinated parties can > collaboratively bump a tx's feerate. A simple example would be a batch > withdrawal from an exchange could be created with a low feerate, and then > multiple users with a vested interest of expedited confirmation could all > "chip in" to raise the feerate with multiple sponsor transactions. > > Having a single ephemeral output seems to create a situation where a > single UTXO has to shoulder the burden of CPFPing a package. Is there some > way we could (possibly later) amend the ephemeral anchor interface to allow > for this kind of collaborative sponsoring? Could you maybe see "chained" > ephemeral anchors that would allow this? > > > On Tue, Oct 18, 2022 at 12:52 PM Jeremy Rubin via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> Excellent proposal and I agree it does capture much of the spirit of >> sponsors w.r.t. how they might be used for V3 protocols. >> >> The only drawbacks I see is they don't work for lower tx version >> contracts, so there's still something to be desired there, and that the >> requirement to sweep the output must be incentive compatible for the miner, >> or else they won't enforce it (pass the buck onto the future bitcoiners). >> The Ephemeral UTXO concept can be a consensus rule (see >> https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate >> UTXO") we add later on in lieu of managing them by incentive, so maybe it's >> a cleanup one can punt. >> >> One question I have is if V3 is designed for lightning, and this is >> designed for lightning, is there any sense in requiring these outputs for >> v3? That might help with e.g. anonymity set, as well as potentially keep >> the v3 surface smaller. >> >> On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> > does that effectively mark output B as unspendable once the child gets >>> confirmed? >>> >>> Not at all. It's a normal spend like before, since the parent has been >>> confirmed. It's completely unrestricted, not being bound to any >>> V3/ephemeral anchor restrictions on size, version, etc. >>> >>> On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < >>> bitcoin-dev@lists.linuxfoundation.org> wrote: >>> Hi Greg, Thank you very much for sharing your proposal! I think there's one thing about the second part of your proposal that I'm missing. Specifically, assuming the scenario of a v3 transaction with three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child transaction spends A and OP_TRUE, does that effectively mark output B as unspendable once the child gets confirmed? If so, isn't the implication therefore that to safely spend a transaction with an ephemeral anchor, all outputs must be spent? Thanks! Best, Arik On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: Hello Everyone, Following up on the "V3 Transaction" discussion here https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html , I would like to elaborate a bit further on some potential follow-on work that would make pinning severely constrained in many setups]. V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under some constraints[0]. This means that when a replacement is to be made and propagated, it costs the expected amount of fees to do so. This is a great start. What's left in this subset of pinning is *package limit* pinning. In other words, a fee-paying transaction cannot enter the mempool due to the existing mempool package it is being added to already being too large in count or vsize. Zooming into the V3 simplified scenario for sake of discussion, though this problem exists in general today: V3 transactions restrict the package limit of a V3 package to one parent and one child. If the parent transaction includes two outputs which can be immediately spent by separate parties, this allows one party to disallow a spend from the other. In Gloria's proposal
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
I'm also very happy to see this proposal, since it gets us closer to having a mechanism that allows the contribution to feerate in an "unauthenticated" way, which seems to be a very helpful feature for vaults and other contracting protocols. One possible advantage of the sponsors interface -- and I'm curious for your input here Greg -- is that with sponsors, assuming we relaxed the "one sponsor per sponsoree" constraint, multiple uncoordinated parties can collaboratively bump a tx's feerate. A simple example would be a batch withdrawal from an exchange could be created with a low feerate, and then multiple users with a vested interest of expedited confirmation could all "chip in" to raise the feerate with multiple sponsor transactions. Having a single ephemeral output seems to create a situation where a single UTXO has to shoulder the burden of CPFPing a package. Is there some way we could (possibly later) amend the ephemeral anchor interface to allow for this kind of collaborative sponsoring? Could you maybe see "chained" ephemeral anchors that would allow this? On Tue, Oct 18, 2022 at 12:52 PM Jeremy Rubin via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > Excellent proposal and I agree it does capture much of the spirit of > sponsors w.r.t. how they might be used for V3 protocols. > > The only drawbacks I see is they don't work for lower tx version > contracts, so there's still something to be desired there, and that the > requirement to sweep the output must be incentive compatible for the miner, > or else they won't enforce it (pass the buck onto the future bitcoiners). > The Ephemeral UTXO concept can be a consensus rule (see > https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate UTXO") > we add later on in lieu of managing them by incentive, so maybe it's a > cleanup one can punt. > > One question I have is if V3 is designed for lightning, and this is > designed for lightning, is there any sense in requiring these outputs for > v3? That might help with e.g. anonymity set, as well as potentially keep > the v3 surface smaller. > > On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> > does that effectively mark output B as unspendable once the child gets >> confirmed? >> >> Not at all. It's a normal spend like before, since the parent has been >> confirmed. It's completely unrestricted, not being bound to any >> V3/ephemeral anchor restrictions on size, version, etc. >> >> On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> Hi Greg, >>> >>> Thank you very much for sharing your proposal! >>> >>> I think there's one thing about the second part of your proposal that >>> I'm missing. Specifically, assuming the scenario of a v3 transaction with >>> three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child >>> transaction spends A and OP_TRUE, does that effectively mark output B as >>> unspendable once the child gets confirmed? If so, isn't the implication >>> therefore that to safely spend a transaction with an ephemeral anchor, all >>> outputs must be spent? Thanks! >>> >>> Best, >>> Arik >>> >>> On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: >>> >>> Hello Everyone, >>> >>> Following up on the "V3 Transaction" discussion here >>> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html >>> , I would like to elaborate a bit further on some potential follow-on work >>> that would make pinning severely constrained in many setups]. >>> >>> V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under >>> some constraints[0]. This means that when a replacement is to be made and >>> propagated, it costs the expected amount of fees to do so. This is a great >>> start. What's left in this subset of pinning is *package limit* pinning. In >>> other words, a fee-paying transaction cannot enter the mempool due to the >>> existing mempool package it is being added to already being too large in >>> count or vsize. >>> >>> Zooming into the V3 simplified scenario for sake of discussion, though >>> this problem exists in general today: >>> >>> V3 transactions restrict the package limit of a V3 package to one parent >>> and one child. If the parent transaction includes two outputs which can be >>> immediately spent by separate parties, this allows one party to disallow a >>> spend from the other. In Gloria's proposal for ln-penalty, this is worked >>> around by reducing the number of anchors per commitment transaction to 1, >>> and each version of the commitment transaction has a unique party's key on >>> it. The honest participant can spend their version with their anchor and >>> package RBF the other commitment transaction safely. >>> >>> What if there's only one version of the commitment transaction, such as >>> in other protocols like duplex payment channels, eltoo? What about multi >>>
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
> (see https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate UTXO") I think I remember you trying to explain this to me a long time ago. Thanks for the callback! > One question I have is if V3 is designed for lightning, and this is designed for lightning, is there any sense in requiring these outputs for v3? That might help with e.g. anonymity set, as well as potentially keep the v3 surface smaller. The fingerprinting angle is yet another thing to consider. There are definitely uses of V3 that do not require ephemeral anchors, and you can save a healthy amount of bytes not requiring them. I think in the cases where RBF of the parent is possible, at least. f.e., I think V3 alone makes splicing robust even in the presence of external inputs, since the commitment tx(s) can (package) RBF the splice at any point. V3 may have enough value-add by itself where the additional bytes and inability to opt out of "transaction sponsor" style bumps may be undesirable. Lastly this would tie deployments of these improvements together. Something to consider. Cheers, Greg On Tue, Oct 18, 2022 at 12:41 PM Jeremy Rubin wrote: > Excellent proposal and I agree it does capture much of the spirit of > sponsors w.r.t. how they might be used for V3 protocols. > > The only drawbacks I see is they don't work for lower tx version > contracts, so there's still something to be desired there, and that the > requirement to sweep the output must be incentive compatible for the miner, > or else they won't enforce it (pass the buck onto the future bitcoiners). > The Ephemeral UTXO concept can be a consensus rule (see > https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate UTXO") > we add later on in lieu of managing them by incentive, so maybe it's a > cleanup one can punt. > > One question I have is if V3 is designed for lightning, and this is > designed for lightning, is there any sense in requiring these outputs for > v3? That might help with e.g. anonymity set, as well as potentially keep > the v3 surface smaller. > > On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> > does that effectively mark output B as unspendable once the child gets >> confirmed? >> >> Not at all. It's a normal spend like before, since the parent has been >> confirmed. It's completely unrestricted, not being bound to any >> V3/ephemeral anchor restrictions on size, version, etc. >> >> On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < >> bitcoin-dev@lists.linuxfoundation.org> wrote: >> >>> Hi Greg, >>> >>> Thank you very much for sharing your proposal! >>> >>> I think there's one thing about the second part of your proposal that >>> I'm missing. Specifically, assuming the scenario of a v3 transaction with >>> three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child >>> transaction spends A and OP_TRUE, does that effectively mark output B as >>> unspendable once the child gets confirmed? If so, isn't the implication >>> therefore that to safely spend a transaction with an ephemeral anchor, all >>> outputs must be spent? Thanks! >>> >>> Best, >>> Arik >>> >>> On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: >>> >>> Hello Everyone, >>> >>> Following up on the "V3 Transaction" discussion here >>> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html >>> , I would like to elaborate a bit further on some potential follow-on work >>> that would make pinning severely constrained in many setups]. >>> >>> V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under >>> some constraints[0]. This means that when a replacement is to be made and >>> propagated, it costs the expected amount of fees to do so. This is a great >>> start. What's left in this subset of pinning is *package limit* pinning. In >>> other words, a fee-paying transaction cannot enter the mempool due to the >>> existing mempool package it is being added to already being too large in >>> count or vsize. >>> >>> Zooming into the V3 simplified scenario for sake of discussion, though >>> this problem exists in general today: >>> >>> V3 transactions restrict the package limit of a V3 package to one parent >>> and one child. If the parent transaction includes two outputs which can be >>> immediately spent by separate parties, this allows one party to disallow a >>> spend from the other. In Gloria's proposal for ln-penalty, this is worked >>> around by reducing the number of anchors per commitment transaction to 1, >>> and each version of the commitment transaction has a unique party's key on >>> it. The honest participant can spend their version with their anchor and >>> package RBF the other commitment transaction safely. >>> >>> What if there's only one version of the commitment transaction, such as >>> in other protocols like duplex payment channels, eltoo? What about multi >>> party payments? >>> >>> In the package RBF proposal,
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Excellent proposal and I agree it does capture much of the spirit of sponsors w.r.t. how they might be used for V3 protocols. The only drawbacks I see is they don't work for lower tx version contracts, so there's still something to be desired there, and that the requirement to sweep the output must be incentive compatible for the miner, or else they won't enforce it (pass the buck onto the future bitcoiners). The Ephemeral UTXO concept can be a consensus rule (see https://rubin.io/public/pdfs/multi-txn-contracts.pdf "Intermediate UTXO") we add later on in lieu of managing them by incentive, so maybe it's a cleanup one can punt. One question I have is if V3 is designed for lightning, and this is designed for lightning, is there any sense in requiring these outputs for v3? That might help with e.g. anonymity set, as well as potentially keep the v3 surface smaller. On Tue, Oct 18, 2022 at 11:51 AM Greg Sanders via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > > does that effectively mark output B as unspendable once the child gets > confirmed? > > Not at all. It's a normal spend like before, since the parent has been > confirmed. It's completely unrestricted, not being bound to any > V3/ephemeral anchor restrictions on size, version, etc. > > On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> Hi Greg, >> >> Thank you very much for sharing your proposal! >> >> I think there's one thing about the second part of your proposal that I'm >> missing. Specifically, assuming the scenario of a v3 transaction with three >> outputs, A, B, and the ephemeral anchor OP_TRUE. If a child transaction >> spends A and OP_TRUE, does that effectively mark output B as unspendable >> once the child gets confirmed? If so, isn't the implication therefore that >> to safely spend a transaction with an ephemeral anchor, all outputs must be >> spent? Thanks! >> >> Best, >> Arik >> >> On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: >> >> Hello Everyone, >> >> Following up on the "V3 Transaction" discussion here >> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html >> , I would like to elaborate a bit further on some potential follow-on work >> that would make pinning severely constrained in many setups]. >> >> V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under >> some constraints[0]. This means that when a replacement is to be made and >> propagated, it costs the expected amount of fees to do so. This is a great >> start. What's left in this subset of pinning is *package limit* pinning. In >> other words, a fee-paying transaction cannot enter the mempool due to the >> existing mempool package it is being added to already being too large in >> count or vsize. >> >> Zooming into the V3 simplified scenario for sake of discussion, though >> this problem exists in general today: >> >> V3 transactions restrict the package limit of a V3 package to one parent >> and one child. If the parent transaction includes two outputs which can be >> immediately spent by separate parties, this allows one party to disallow a >> spend from the other. In Gloria's proposal for ln-penalty, this is worked >> around by reducing the number of anchors per commitment transaction to 1, >> and each version of the commitment transaction has a unique party's key on >> it. The honest participant can spend their version with their anchor and >> package RBF the other commitment transaction safely. >> >> What if there's only one version of the commitment transaction, such as >> in other protocols like duplex payment channels, eltoo? What about multi >> party payments? >> >> In the package RBF proposal, if the parent transaction is identical to an >> existing transaction in the mempool, the parent will be detected and >> removed from the package proposal. You are then left with a single V3 child >> transaction, which is then proposed for entry into the mempool. In the case >> of another parent output already being spent, this is simply rejected, >> regardless of feerate of the new child. >> >> I have two proposed solutions, of which I strongly prefer the latter: >> >> 1) Expand a carveout for "sibling eviction", where if the new child is >> paying "enough" to bump spends from the same parent, it knocks its sibling >> out of the mempool and takes the one child slot. This would solve it, but >> is a new eviction paradigm that would need to be carefully worked through. >> >> 2) Ephemeral Anchors (my real policy-only proposal) >> >> Ephemeral Anchors is a term which means an output is watermarked as an >> output that MUST be spent in a V3 package. We mark this anchor by being the >> bare script `OP_TRUE` and of course make these outputs standard to relay >> and spend with empty witness data. >> >> Also as a simplifying assumption, we require the parent transaction with >> such an output to be 0-fee. This makes mempool
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
> does that effectively mark output B as unspendable once the child gets confirmed? Not at all. It's a normal spend like before, since the parent has been confirmed. It's completely unrestricted, not being bound to any V3/ephemeral anchor restrictions on size, version, etc. On Tue, Oct 18, 2022 at 11:47 AM Arik Sosman via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > Hi Greg, > > Thank you very much for sharing your proposal! > > I think there's one thing about the second part of your proposal that I'm > missing. Specifically, assuming the scenario of a v3 transaction with three > outputs, A, B, and the ephemeral anchor OP_TRUE. If a child transaction > spends A and OP_TRUE, does that effectively mark output B as unspendable > once the child gets confirmed? If so, isn't the implication therefore that > to safely spend a transaction with an ephemeral anchor, all outputs must be > spent? Thanks! > > Best, > Arik > > On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: > > Hello Everyone, > > Following up on the "V3 Transaction" discussion here > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html > , I would like to elaborate a bit further on some potential follow-on work > that would make pinning severely constrained in many setups]. > > V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under > some constraints[0]. This means that when a replacement is to be made and > propagated, it costs the expected amount of fees to do so. This is a great > start. What's left in this subset of pinning is *package limit* pinning. In > other words, a fee-paying transaction cannot enter the mempool due to the > existing mempool package it is being added to already being too large in > count or vsize. > > Zooming into the V3 simplified scenario for sake of discussion, though > this problem exists in general today: > > V3 transactions restrict the package limit of a V3 package to one parent > and one child. If the parent transaction includes two outputs which can be > immediately spent by separate parties, this allows one party to disallow a > spend from the other. In Gloria's proposal for ln-penalty, this is worked > around by reducing the number of anchors per commitment transaction to 1, > and each version of the commitment transaction has a unique party's key on > it. The honest participant can spend their version with their anchor and > package RBF the other commitment transaction safely. > > What if there's only one version of the commitment transaction, such as in > other protocols like duplex payment channels, eltoo? What about multi party > payments? > > In the package RBF proposal, if the parent transaction is identical to an > existing transaction in the mempool, the parent will be detected and > removed from the package proposal. You are then left with a single V3 child > transaction, which is then proposed for entry into the mempool. In the case > of another parent output already being spent, this is simply rejected, > regardless of feerate of the new child. > > I have two proposed solutions, of which I strongly prefer the latter: > > 1) Expand a carveout for "sibling eviction", where if the new child is > paying "enough" to bump spends from the same parent, it knocks its sibling > out of the mempool and takes the one child slot. This would solve it, but > is a new eviction paradigm that would need to be carefully worked through. > > 2) Ephemeral Anchors (my real policy-only proposal) > > Ephemeral Anchors is a term which means an output is watermarked as an > output that MUST be spent in a V3 package. We mark this anchor by being the > bare script `OP_TRUE` and of course make these outputs standard to relay > and spend with empty witness data. > > Also as a simplifying assumption, we require the parent transaction with > such an output to be 0-fee. This makes mempool reasoning simpler in case > the child-spend is somehow evicted, guaranteeing the parent will be as well. > > Implications: > > a) If the ephemeral anchor MUST be spent, we can allow *any* value, even > dust, even 0, without worrying about bloating the utxo set. We relax this > policy for maximum smart contract flexibility and specification simplicity.. > > b) Since this anchor MUST be spent, any spending of other outputs in the > same parent transaction MUST directly double-spend prior spends of the > ephemeral anchor. This causes the 1 block CSV timelock on outputs to be > removed in these situations. This greatly magnifies composability of smart > contracts, as now we can do things like safely splice directly into new > channels, into statechains, your custodial wallet account, your cold > wallet, wherever, without requiring other wallets to support arbitrary > scripts. Also it hurts that 1 CSV time locked scripts may not be miniscript > compatible to begin with... > > c) *Anyone* can bump the transaction, without any transaction key > material. This is
Re: [bitcoin-dev] Ephemeral Anchors: Fixing V3 Package RBF againstpackage limit pinning
Hi Greg, Thank you very much for sharing your proposal! I think there's one thing about the second part of your proposal that I'm missing. Specifically, assuming the scenario of a v3 transaction with three outputs, A, B, and the ephemeral anchor OP_TRUE. If a child transaction spends A and OP_TRUE, does that effectively mark output B as unspendable once the child gets confirmed? If so, isn't the implication therefore that to safely spend a transaction with an ephemeral anchor, all outputs must be spent? Thanks! Best, Arik On Tue, Oct 18, 2022, at 6:52 AM, Greg Sanders via bitcoin-dev wrote: > Hello Everyone, > > > Following up on the "V3 Transaction" discussion here > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-September/020937.html > , I would like to elaborate a bit further on some potential follow-on work > that would make pinning severely constrained in many setups]. > > > V3 transactions may solve bip125 rule#3 and rule#5 pinning attacks under some > constraints[0]. This means that when a replacement is to be made and > propagated, it costs the expected amount of fees to do so. This is a great > start. What's left in this subset of pinning is *package limit* pinning. In > other words, a fee-paying transaction cannot enter the mempool due to the > existing mempool package it is being added to already being too large in > count or vsize. > > > Zooming into the V3 simplified scenario for sake of discussion, though this > problem exists in general today: > > > V3 transactions restrict the package limit of a V3 package to one parent and > one child. If the parent transaction includes two outputs which can be > immediately spent by separate parties, this allows one party to disallow a > spend from the other. In Gloria's proposal for ln-penalty, this is worked > around by reducing the number of anchors per commitment transaction to 1, and > each version of the commitment transaction has a unique party's key on it. > The honest participant can spend their version with their anchor and package > RBF the other commitment transaction safely. > > > What if there's only one version of the commitment transaction, such as in > other protocols like duplex payment channels, eltoo? What about multi party > payments? > > > In the package RBF proposal, if the parent transaction is identical to an > existing transaction in the mempool, the parent will be detected and removed > from the package proposal. You are then left with a single V3 child > transaction, which is then proposed for entry into the mempool. In the case > of another parent output already being spent, this is simply rejected, > regardless of feerate of the new child. > > > I have two proposed solutions, of which I strongly prefer the latter: > > > 1) Expand a carveout for "sibling eviction", where if the new child is paying > "enough" to bump spends from the same parent, it knocks its sibling out of > the mempool and takes the one child slot. This would solve it, but is a new > eviction paradigm that would need to be carefully worked through. > > > 2) Ephemeral Anchors (my real policy-only proposal) > > > Ephemeral Anchors is a term which means an output is watermarked as an output > that MUST be spent in a V3 package. We mark this anchor by being the bare > script `OP_TRUE` and of course make these outputs standard to relay and spend > with empty witness data. > > > Also as a simplifying assumption, we require the parent transaction with such > an output to be 0-fee. This makes mempool reasoning simpler in case the > child-spend is somehow evicted, guaranteeing the parent will be as well. > > > Implications: > > > a) If the ephemeral anchor MUST be spent, we can allow *any* value, even > dust, even 0, without worrying about bloating the utxo set. We relax this > policy for maximum smart contract flexibility and specification simplicity.. > > > b) Since this anchor MUST be spent, any spending of other outputs in the same > parent transaction MUST directly double-spend prior spends of the ephemeral > anchor. This causes the 1 block CSV timelock on outputs to be removed in > these situations. This greatly magnifies composability of smart contracts, as > now we can do things like safely splice directly into new channels, into > statechains, your custodial wallet account, your cold wallet, wherever, > without requiring other wallets to support arbitrary scripts. Also it hurts > that 1 CSV time locked scripts may not be miniscript compatible to begin > with... > > > c) *Anyone* can bump the transaction, without any transaction key material. > This is essentially achieving Jeremy's Transaction Sponsors > (https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-September/018168.html) > proposal without consensus changes. As long as someone gets a fully signed > parent, they can execute a bump with minimal wallet tooling. If a transaction > author doesn’t
