CTV+CSFS: Can we reach consensus on a first step towards covenants?

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@jamesob

VERIFY is also important for upgradeability; if you don’t have the <32-byte-hash> parameter, you can’t make the opcode upgradeable.

Now maybe in a tapscript context that’s okay because you’ve got so much unused opcode space.

Good point, but you’re correct I’ve basically stopped thinking about these kinds of details because we have so many upgrade hooks. Let’s use them!

@jamesob

I’m just trying to figure out why you want it, since all the uses of CTV I’m familiar with are VERIFYs

The use-cases I’m thinking about that involve the CTV + CSFS combo means we can elide bringing the hash into the witness data, saving ~32WU. State channels, payment channels, statechains, pre-signed HTLC transactions, PTLC transactions. Probably more, but probably most of the CTV + CSFS intersection of functionality.

The tradeoff here is 1WU(?) in the tapscript CTV case, which would apply to things like Ark, Timeout Trees, settlement path in ln-symmetry(et al.), anywhere where authorization isn’t required, just precommitment. I don’t find this a compelling savings if we have to choose just one.

And if VERIFY behavior is still desired, you could still softfork a NOP, just in tapscript circumstances.

@jamesob

But I think the idea that it would replace CTV as-is is sort of a different proposal.

I’m much more interested in CTV + CSFS than CTV alone, so there lies some design bias.

@jamesob

Again, not trying to be glib here but is there a more specific reason than “each reviewer has to review about 15 marginal lines of not-substantially-novel code?” What about legacy is so complicated that it really moves the needle?

I’m thinking about it from another direction: Designing BIP119 from scratch, how should we build it? Legacy script (short-hand for non-segwit, not NOPs) is a dumpster fire, and it shouldn’t be touched unless necessary.

If it saves no vbytes, makes no operations safer, doesn’t make the changes easier to understand for reviewers, why would we build it this way?

@jamesob

Please grant me the goodwill to admit it’s a reasonable thought that if chainspace ever does become massively short, congestion control is a good escape hatch to have on hand - even outside of the use for miners today.

I think bare CTV in any form is one of the least motivated proposals I’ve seen in a long while, but if it’s going to happen, I want it to happen in the way that’s least damaging in terms of maintenance of Bitcoin script. I believe my proposal is one way to do it without changing any known capabilities from the original.