> Can you remind me in what way Ark would benefit from sibling commitments?
In all honesty, sibling commitments have minimal benefit to Ark, so in retrospect, it is not a great example. The only place sibling commitments could theoretically benefit Ark is by reducing the cost of spending a connector output, since each connector output is created in advance to be spent by a specific forfeit transaction (for an on-chain withdrawal). Realizing the cost savings, though, would require an explicit Pay-to-Bare-Tapscript or Pay-to-TemplateHash witness program, akin to bare CTV. This would save ~16vb, but only in the rare event the operator needs to publish the forfeit transaction. Josh * (1) and (2) are only compatible with script-based vector commitments, since tapleaf commitments would create a hash cycle. On Thu, May 28, 2026 at 10:14 AM Greg Sanders <[email protected]> wrote: > > Ark > > Can you remind me in what way Ark would benefit from sibling commitments? > > Greg > > On Wednesday, May 27, 2026 at 4:29:30 PM UTC-4 Josh Doman wrote: > >> Like many others, I'm interested in the OP_CTV and OP_TEMPLATEHASH >> proposals. One subtle difference is that OP_TEMPLATEHASH does not enable >> sibling-aware covenants, like those used in BitVM, Ark, and (potentially) >> LN-Symmetry.[1] This requires a connector output and a sibling prevout >> commitment. This way, additional conditions can be added to the covenant, >> or it can be invalidated altogether. >> >> Personally, I find unsatisfactory the method by which OP_CTV achieves >> this (by committing to the scriptSigs), and I appreciate the simplicity of >> OP_TEMPLATEHASH (TH) and the fact that it requires no additional >> pre-computation. >> >> The purpose of this post isn't to suggest a modification to TH but to >> attempt to list all the ways sibling-aware covenants could be achieved. I >> found this helpful to understand the tradeoffs that surround this >> capability. >> >> The first five options entail an additional commitment to TH: >> 1.* scriptSigs*: precompute a hash of all scriptSigs. >> 2. *Dynamic MuHash*: precompute a MuHash commitment to all indexed >> prevouts and then remove the prevout at the current index. >> 3. *All-but-first*: restrict execution to the first input and commit to >> all other prevouts. >> 4. *First-only*: commit to the prevout at the first index, if the >> current index is non-zero. >> 5. *Next-only*: commit to the prevout at the next index, if present. >> >> An alternative approach is to create a new witness program, which >> indirectly enforces a sibling prevout commitment: >> 6. * Pay-to-Prevout-Anchor (P2PA):* an anyone-can-spend output that *cannot >> be created *unless the output's program is the hash of the prevout at >> the same index in that transaction. >> >> The final options involve new introspection opcodes (not exhaustive): >> 7. *OP_TXHASH*: a general introspection opcode that can push a hash that >> commits to one or more prevouts at specific indices. >> 8. *OP_CAT*: a simple opcode that enables introspection via complex >> script. >> >> I won't go into the pros and cons of each option, except to say that I >> think Option 5 strikes a nice balance between minimalism, pragmatism, and >> flexibility.[2] >> >> Mostly, I wanted to list what options I think exist. If I missed any, >> please let me know! >> >> Best, >> Josh >> >> *[1] Eliminating the 2x-delay problem in LN-Symmetry requires a >> contract-level relative timelock (CLRT) and a sibling-aware covenant. CLRT >> capabilities remain an active area of research and may not exist in the >> first iteration of LN-Symmetry.* >> >> *See: >> https://delvingbitcoin.org/t/contract-level-relative-timelocks-or-lets-talk-about-ancestry-proofs-and-singletons/1353 >> <https://delvingbitcoin.org/t/contract-level-relative-timelocks-or-lets-talk-about-ancestry-proofs-and-singletons/1353>* >> >> *[2] Option 5 (Next-Only) strikes me as a balanced option for several >> reasons:* >> *- Identical to TH in the common single-input use case.* >> *- Solves for the two-input sibling-aware covenant common to L2 >> protocols.* >> *- Leaves the door open to multi-input covenants with no sibling >> commitments.* >> *- Requires no additional pre-computation.* >> >> -- > You received this message because you are subscribed to a topic in the > Google Groups "Bitcoin Development Mailing List" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/bitcoindev/uyRpzE6IFOQ/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/c00f0fdf-950b-4ff8-a502-eeb1be02c510n%40googlegroups.com > <https://groups.google.com/d/msgid/bitcoindev/c00f0fdf-950b-4ff8-a502-eeb1be02c510n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. 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