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From: Johnson Lau <jl2012@xbt.hk>
In-Reply-To: <201710010113.30518.luke@dashjr.org>
Date: Mon, 2 Oct 2017 05:32:56 +0800
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Message-Id: <30B31B43-B603-4793-BDFB-B7E25FD96D1B@xbt.hk>
References: <201710010113.30518.luke@dashjr.org>
To: Luke Dashjr <luke@dashjr.org>,
	bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Version 1 witness programs (first draft)
Precedence: list

So there are 3 proposals with similar goal but different designs. I try =
to summarise some questions below:

1. How do we allow further upgrade within v1 witness? Here are some =
options:
a. Minor version in witness. (Johnson / Luke) I prefer this way, but we =
may end up with many minor versions.
b. OP_RETURNTRUE (Luke). I proposed this in an earlier version of BIP114 =
but now I think it doesn=E2=80=99t interact well with signature =
aggregation, and I worry that it would have some other unexpected =
effects.
c. Generalised NOP method: user has to provide the returned value, so =
even VERIFY-type code could do anything

2. Do we want to allow signature-time commitment of extra scripts?
I think all proposals allow this, just with different way
a. Tail-call semantics with CHECKSIGFROMSTACK (Mark). I think this is =
too rigid as it works only with specially designed scriptPubKey
b. scriptWitCode: extra scripts are put in some fixed location in =
witness (Johnson). This makes sure static analysability.
c. Extra-data as script in OP_CHECKSIG (Luke)

3. Do we want to allow static analysis of sigop?
BIP114 and the related proposals are specifically designed to allow =
static analysis of sigop. I think this was one of the main reason of =
OP_EVAL not being accepted. This was also the main reason of Ethereum =
failing to do a DAO hacker softfork, leading to the ETH/ETC split. I=E2=80=
=99m not sure if we really want to give up this property. Once we do it, =
we have to support it forever.

=E2=80=94=E2=80=94
Johnson=