Date: Fri, 10 May 2019 05:38:52 +0000
To: Johnson Lau <jl2012@xbt.hk>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Message-ID: <-3ac1EW7T8KOkUw6DK2Ejq83DiawO15bwaZJ79kw1U81w6sPCCkS2pAcTXtmLr8eOkohU7T8JJbW0K8dj690UYC9ffIqAqzP8e7fjbOqG70=@protonmail.com>
In-Reply-To: <DBADD452-6DAE-46D4-9511-69F8EAA02FFB@xbt.hk>
References: <CAPg+sBg6Gg8b7hPogC==fehY3ZTHHpQReqym2fb4XXWFpMM-pQ@mail.gmail.com>
	<201905062017.11396.luke@dashjr.org>
	<sujR-1TPC3DI-bNyQD2U5c5E0qkkfi6WezKQOfB9YgP7UbLj3x-maV0ooIqvJ4C2V_yjkrq78F7QqIZ5LyoZuSKcpC08RFWapH2k-FF3_zc=@protonmail.com>
	<DBADD452-6DAE-46D4-9511-69F8EAA02FFB@xbt.hk>
Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>,
	Pieter Wuille <pieter.wuille@gmail.com>
Subject: Re: [bitcoin-dev] Taproot proposal
Precedence: list

Good morning Johnson,


> > > Some way to sign an additional script (not committed to by the witnes=
s
> > > program) seems like it could be a trivial addition.
> >
> > It seems to me the annex can be used for this, by having it contain bot=
h the script and the signature somehow concatenated.
>
> This is not possible since the whole annex is signed. It is possible if t=
he signed =E2=80=9Cscript=E2=80=9D does not require further input, like per=
-input lock-time, relative lock-time, check block hash

I understand, you are correct.

Possibly the correct way would be to use another leaf version.
The "script" of such a new leaf version would not actually be a script, but=
 a delegation key.
Then for this leaf version the actual script and signature from the delegat=
ion key attesting that script would be on top of the witness stack that wil=
l be used by the actual script.
This has the nice property that the existence of a delegation key is hidden=
 from the output, and that if an alternate script is in the MAST (as an alt=
ernative to the delegation), use of that alternate script does not reveal t=
hat delegation could have been possible.

Regards,
ZmnSCPxj