Brandon Black <free...@reardencode.com> writes: > On 2023-10-20 (Fri) at 14:10:37 +1030, Rusty Russell via bitcoin-dev wrote: >> I've done an exploration of what would be required (given >> OP_TX/OP_TXHASH or equivalent way of pushing a scriptPubkey on the >> stack) to usefully validate Taproot outputs in Bitcoin Script. Such >> functionality is required for usable vaults, at least. > > So you're proposing this direction as an alternative to the more > constrained OP_UNVAULT that replaces a specific leaf in the taptree in a > specific way? I think the benefits of OP_UNVAULT are pretty big vs. a > generic construction (e.g. ability to unvault multiple inputs sharing > the same scriptPubkey to the same output).
I would have to write the scripts exactly (and I'm already uncomfortable that I haven't actually tested the ones I wrote so far!) to properly evaluate. In general, script makes it hard to do N-input evaluation (having no iteration). It would be useful to attempt this though, as it might enlighted us as to OP_TXHASH input selection: for example, we might want to have an "all *but* one input" mode for this kind of usage. Dealing with satsoshi amounts is possible, but really messy (that's my next post). >> TL;DR: if we have OP_TXHASH/OP_TX, and add OP_MULTISHA256 (or OP_CAT), >> OP_KEYADDTWEAK and OP_LESS (or OP_CONDSWAP), and soft-fork weaken the >> OP_SUCCESSx rule (or pop-script-from-stack), we can prove a two-leaf >> tapscript tree in about 110 bytes of Script. This allows useful >> spending constraints based on a template approach. > > I agree that this is what is needed. I started pondering this in > response to some discussion about the benefits of OP_CAT or OP_2SHA256 > for BitVM. Given these examples, I think it's clear that OP_MULTISHA256 is almost as powerful as OP_CAT, without the stack limit problems. And OP_2SHA256 is not sufficient in general for CScriptNum generation, for example. > Personally I'd use OP_TAGGEDCATHASH that pops a tag (empty tag can be > special cased to plain sha256) and a number (n) of elements to hash, > then tagged-hashes the following 'n' elements from the stack. That's definitely a premature optimization to save two opcodes. Cheers, Rusty. _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
