Subject: Re: [bitcoin-dev] Standardisation of an unstructured taproot annex

From: Joost Jager <[email-masked]>
Date: Tue, 20 Jun 2023 14:50:47 +0200

Hi Antoine,

On Sun, Jun 18, 2023 at 10:32 PM Antoine Riard <[email-masked]>
wrote:

> > * Opt-in annex (every input must commit to an annex even if its is
> empty) -> make sure existing multi-party protocols remain unaffected
>
> By requiring every input to commit to an annex even if it is empty, do you
> mean rejecting a transaction where the minimal annex with its 0x50 tag is
> absent ?
>

No what I meant, and what was mentioned by Greg in a previous email, is
that either none of the inputs have an annex, or all of them have one.

So if you're part of a multi-party transaction and you don't commit to an
annex, you can be sure that no version of that tx will appear where another
signer surprises you with a potentially large annex.

For future protocols that rely on the annex, everyone would need to opt-in
by committing to an annex (which can be empty just to signal opt-in).

Joost