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From: Johnson Lau <jl2012@xbt.hk>
In-Reply-To: <878t1kcet7.fsf@gmail.com>
Date: Sat, 24 Nov 2018 16:13:46 +0800
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Message-Id: <9A562EB2-7041-48E5-9D77-4337B24C3C84@xbt.hk>
References: <CAPg+sBhuPG-2GXc+Bp0yv5ywry2fk56LPLT4AY0Kcs+YEoz4FA@mail.gmail.com>
	<87k1l6d6lb.fsf@gmail.com>
	<20181123060404.fu4eyzcynbppmjcy@erisian.com.au>
	<878t1kcet7.fsf@gmail.com>
To: Christian Decker <decker.christian@gmail.com>,
	bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Precedence: list


> On 23 Nov 2018, at 5:40 PM, Christian Decker via bitcoin-dev =
<bitcoin-dev@lists.linuxfoundation.org> wrote:
>=20
> Anthony Towns <aj@erisian.com.au> writes:
>> Commiting to just the sequence numbers seems really weird to me; it
>> only really prevents you from adding inputs, since you could still
>> replace any input that was meant to be there by almost any arbitrary
>> other transaction...
>=20
> It's a really roundabout way of committing to the inputs, I
> agree. I'm actually wondering if it makes sense to correct that
> additional blanked field in BIP118 at all since it seems there is no
> real use-case for NOINPUT that doesn't involve blanking the
> `hashSequence` as well.

I think we just make it as simple as this: Always commit to sequence of =
the same input. Commit to hashSequence if and only if all inputs and all =
outputs are signed.

The next-generation SIGHASH will introduce not only NOINPUT, but also =
signing of fees, previous scriptPubKey, and all input values, etc. So it =
won=E2=80=99t be a simple hack over BIP143. BIP118 might be better =
changed to be an informational BIP, focus on the rationale and examples =
of NOINPUT, and be cross-referenced with the consensus BIP.=