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From: Johnson Lau <jl2012@xbt.hk>
In-Reply-To: <34949746-c0c9-7f14-0e92-69d5a7d44b04@voskuil.org>
Date: Thu, 17 Nov 2016 23:40:05 +0800
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To: Eric Voskuil <eric@voskuil.org>,
	bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP30 and BIP34 interaction (was Re: [BIP
	Proposal] Buried Deployments)
Precedence: list


> On 17 Nov 2016, at 20:22, Eric Voskuil via bitcoin-dev =
<bitcoin-dev@lists.linuxfoundation.org> wrote:
>=20
>=20
> Given that hash collisions are unquestionably possible,=20

Everything you said after this point is irrelevant.

Having hash collision is **by definition** a consensus failure, or a =
hardfork. You could replace the already-on-chain tx with the collision =
and create 2 different versions of UTXOs (if the colliding tx is valid), =
or make some nodes to accept a fork with less PoW (if the colliding tx =
is invalid, or making the block invalid, such as being to big). To put =
it simply, the Bitcoin protocol is broken. So with no doubt, Bitcoin =
Core and any implementation of the Bitcoin protocol should assume SHA256 =
collision is unquestionably **impossible**. If some refuse to make such =
assumption, they should have introduced an alternative hash algorithm =
and somehow run it in parallel with SHA256 to prevent the consensus =
failure.

jl2012=