From: Rusty Russell <rusty@rustcorp.com.au>
To: James O'Beirne <james.obeirne@gmail.com>, Bitcoin Protocol Discussion
 <bitcoin-dev@lists.linuxfoundation.org>
In-Reply-To: <CAPfvXfK7a5To=-n+TOY34KZn2T=Dkf5M1S3eFCNmug8xuE9rTw@mail.gmail.com>
References: <ZTtgFPG4tTeZMnYn@erisian.com.au> <87r0lfz6zp.fsf@rustcorp.com.au>
 <CAPfvXfK7a5To=-n+TOY34KZn2T=Dkf5M1S3eFCNmug8xuE9rTw@mail.gmail.com>
Date: Tue, 31 Oct 2023 12:54:27 +1030
Message-ID: <87v8anr0kk.fsf@rustcorp.com.au>
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Subject: Re: [bitcoin-dev] Examining ScriptPubkeys in Bitcoin Script
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"James O'Beirne" <james.obeirne@gmail.com> writes:
> On Sat, Oct 28, 2023 at 12:51=E2=80=AFAM Rusty Russell via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> But AFAICT there are multiple perfectly reasonable variants of vaults,
>> too.  One would be:
>>
>> 1. master key can do anything
>> 2. OR normal key can send back to vault addr without delay
>> 3. OR normal key can do anything else after a delay.
>>
>> Another would be:
>> 1. normal key can send to P2WPKH(master)
>> 2. OR normal key can send to P2WPKH(normal key) after a delay.
>>
>
> I'm confused by what you mean here. I'm pretty sure that BIP-345 VAULT
> handles the cases that you're outlining, though I don't understand your
> terminology -- "master" vs. "normal", and why we are caring about P2WPKH
> vs. anything else. Using the OP_VAULT* codes can be done in an arbitrary
> arrangement of tapleaves, facilitating any number of vaultish spending
> conditions, alongside other non-VAULT leaves.

I was thinking from a user POV: the "master" key is the one they keep
super safe in case of emergencies, the "normal" is the delayed spend
key.

OP_VAULT certainly can encapsulate this, but I have yet to do the kind
of thorough review that I'd need to evaluate the various design
decisions.

> Well, I found the vault BIP really hard to understand.  I think it wants
>> to be a new address format, not script opcodes.
>>
>
> Again confused here. This is like saying "CHECKLOCKTIMEVERIFY wants to be=
 a
> new address format, not a script opcode."

I mean in an ideal world, Bitcoin Script would be powerful enough to
implement vaults, and once a popular use pattern emerged we'd introduce
a new address type, defined to expand to that template.  Like P2WPK or
P2PKH.

Sadly, we're not in that world!  BIP 345 introduces a number of separate
mechanisms, such as limited script delegation, iteration and amount
arithmetic which are not expressible in Script (ok, amount arithmetic
kind of is, but ick!).

To form a real opinion, I need to consider all these elements, and
whether they should exist inside OP_VAULT, or as separate things.
That's a slow process, sorry :(

> That said, I'm sure some VAULT patterns could be abstracted into the
> miniscript/descriptor layer to good effect.

That would be very interesting, but hard.  Volunteers? :)

Cheers,
Rusty.