Re: [bitcoin-dev] Test cases for Taproot signature message

From: Riccardo Casatta <riccardo.casatta@gmail•com>
To: Giacomo Caironi <giacomo.caironi@gmail•com>,
	 Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Test cases for Taproot signature message
Date: Fri, 17 Sep 2021 09:07:48 +0200	[thread overview]
Message-ID: <CADabwBB4jmwqyJAqfghWTGLiCHFYXset5ZvKB36Q2FkMomJCtQ@mail.gmail.com> (raw)
In-Reply-To: <CACHAfwcJrf8kc9+=2+ekjuPTPjW8T6qJS538QQ2DJedAn-XxKA@mail.gmail.com>

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Hi Giacomo,

I wrote the rust implementation of bitcoin signature messages and to
double-check I created some test vectors you can see at
https://github.com/rust-bitcoin/rust-bitcoin/blob/b7f984972ad6cb4942827c2b7c401f590588cdcf/src/util/sighash.rs#L689-L799.
These vectors have been created printing intermediate results from
https://github.com/bitcoin/bitcoin/blob/6401de0133e32a641ed9e78a85b3aa337c75d190/test/functional/feature_taproot.py

Il giorno gio 16 set 2021 alle ore 23:40 Giacomo Caironi via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> ha scritto:

> Hi,
> recently I have worked on a python implementation of bitcoin signature
> messages, and I have found that there was way better documentation about
> Segwit signature message than Taproot.
>
> 1) Segwit signature message got its own BIP, completed with test cases
> regarding only that specific function; Taproot on the other hand has the
> signature message function defined in BIP 341 and the test vectors in a
> different BIP (341). This is confusing. Shouldn't we create a different BIP
> only for Taproot signature message exactly like Segwit?
>
> 2) The test vectors for Taproot have no documentation and, most
> importantly, they are not atomic, in the sense that they do not target a
> specific part of the taproot code but all of it. This may not be a very big
> problem, but for signature verification it is. Because there are hashes
> involved, we can't really debug why a signature message doesn't pass
> validation, either it is valid or it is not. BIP 143 in this case is really
> good, because it provides hash preimages, so it is possible to debug the
> function and see where something went wrong. Because of this, writing the
> Segwit signature hash function took a fraction of the time compared to
> Taproot.
>
> If this idea is accepted I will be more than happy to write the test cases
> for Taproot.
>
> BTW this is the first time I contribute to Bitcoin, let me know if I was
> rude or did something wrong. Moreover english is not my first language, so
> I apologize if I wrote something awful above
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-- 
Riccardo Casatta - @RCasatta <https://twitter.com/RCasatta>

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