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From: Tier Nolan <tier.nolan@gmail.com>
Date: Thu, 17 Nov 2016 10:22:28 +0000
Message-ID: <CAE-z3OXfJa3Lewtrafm25bdfPa=eiarOAXBNbgc3ccTi7Qoe6A@mail.gmail.com>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary=001a1147a40414e97b05417c919e
Subject: Re: [bitcoin-dev] BIP30 and BIP34 interaction (was Re: [BIP
 Proposal] Buried Deployments)
Precedence: list

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On Thu, Nov 17, 2016 at 12:43 AM, Eric Voskuil <eric@voskuil.org> wrote:

> > This means that all future transactions will have different txids...
> rules do guarantee it.
>
> No, it means that the chance is small, there is a difference.
>

I think we are mostly in agreement then?  It is just terminology.

In terms of discussing the BIP, barring a hash collision, it does make
duplicate txids impossible.

Given that a hash collision is so unlikely, the qualifier should be added
to those making claims that require hash collisions rather than those who
assume that they aren't possible.

You could have said "However nothing precludes different txs from having
the same hash, but it requires a hash collision".

Thinking about it, a re-org to before the enforcement height could allow
it.  The checkpoints protect against that though.


> As such this is not something that a node
> can just dismiss.


The security of many parts of the system is based on hash collisions not
being possible.

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">On Thu, Nov 17, 2016 at 12:43 AM, Eric Voskuil <span dir=3D"ltr">&lt;<a=
 target=3D"_blank" href=3D"mailto:eric@voskuil.org">eric@voskuil.org</a>&gt=
;</span> wrote:<br><blockquote style=3D"margin:0px 0px 0px 0.8ex;border-lef=
t:1px solid rgb(204,204,204);padding-left:1ex" class=3D"gmail_quote">&gt; T=
his means that all future transactions will have different txids...<br>
rules do guarantee it.<br>
<br>
No, it means that the chance is small, there is a difference.<br></blockquo=
te><div><br></div><div>I think we are mostly in agreement then?=C2=A0 It is=
 just terminology.<br><br></div><div>In terms of discussing the BIP, barrin=
g a hash collision, it does make duplicate txids impossible.<br><br></div><=
div>Given that a hash collision is so unlikely, the qualifier should be add=
ed to those making claims that require hash collisions rather than those wh=
o assume that they aren&#39;t possible.<br><br></div><div>You could have sa=
id &quot;<span class=3D"gmail-im">However nothing precludes different txs f=
rom having the same hash</span>, but it requires a hash collision&quot;.<br=
><br></div><div>Thinking about it, a re-org to before the enforcement heigh=
t could allow it.=C2=A0 The checkpoints protect against that though.<br></d=
iv><div>=C2=A0<br></div><blockquote style=3D"margin:0px 0px 0px 0.8ex;borde=
r-left:1px solid rgb(204,204,204);padding-left:1ex" class=3D"gmail_quote">A=
s such this is not something that a node<br>
can just dismiss. </blockquote><div><br></div><div>The security of many par=
ts of the system is based on hash collisions not being possible.<br></div><=
/div></div></div>

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