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From: Hector Chu <hectorchu@gmail.com>
Date: Sat, 1 Aug 2015 09:43:56 +0100
Message-ID: <CAAO2FKH4txfNxz9H51YPm+5hMaZ+w16gBhpF5ztvbef4ar3K8w@mail.gmail.com>
To: Gregory Maxwell <gmaxwell@gmail.com>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Block size hard fork
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On 1 August 2015 at 01:17, Gregory Maxwell <gmaxwell@gmail.com> wrote:

> One can quite easily transact in a way to intentionally produce such a
> split to seperate the existance of your coins onto the seperate forks;
> just as anyone would need to do to perform a reorg-and-respend attack
> on a single blockchain.
>

Right. Why anyone would want to do this intentionally, however, is not
clear. The coins would be worth less as they wouldn't be fungible across
the chains anymore.

Additionally, new coins will be issued, along with fees, on both
> chains. These new outputs become spendable after 100 blocks, and any
> transaction spending them can exist exclusively on one chain.
>

This is something that hadn't entered my mind when I made my assertions. At
the moment I can't see any way to avoid this fact.

Also any transaction whos casual history extends from one of the above
> cases can exist only on one chain. This also means that someone who
> has single-chain coins (via a conflict or from coinbase outputs) can
> pay small amount to many users to get their wallets to consume them
> and make more of the transactions single chain only-- if they wanted
> the process to happen faster.
>

Wallets could detect this and notify the user. Due to Gresham's Law, I'll
admit the observation that these outputs would likely get spent in
preference (as they are less fungible), but whether the payee would be
happy to accept them is a different matter.

> Miners will migrate to the bigger chain in search of higher profits due
> to higher volume of fees
>
> The migration remark is a considerable oversimplification. Imagine if
> I released a version of the software programmed to reassign ownership
> of a million of the earliest created unmoved coins to me at block
> 400k, and then after that I made transaction to pay 5 coin/block in
> fees. Would miners move to this chain?  It pays more in fees!
>

Well in your example they wouldn't, because they know that your version
wouldn't be accepted by the economic majority. But it's not as clear cut
for the larger blocks case. They may move over gradually as they see the
new chain gain acceptance, demonstrated by the higher trading volume on it.

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On 1=
 August 2015 at 01:17, Gregory Maxwell <span dir=3D"ltr">&lt;<a href=3D"mai=
lto:gmaxwell@gmail.com" target=3D"_blank">gmaxwell@gmail.com</a>&gt;</span>=
 wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bor=
der-left:1px #ccc solid;padding-left:1ex">One can quite easily transact in =
a way to intentionally produce such a<br>
split to seperate the existance of your coins onto the seperate forks;<br>
just as anyone would need to do to perform a reorg-and-respend attack<br>
on a single blockchain.<br></blockquote><div><br></div><div>Right. Why anyo=
ne would want to do this intentionally, however, is not clear. The coins wo=
uld be worth less as they wouldn&#39;t be fungible across the chains anymor=
e.</div><div><br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 =
0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Additionally, new coins will be issued, along with fees, on both<br>
chains. These new outputs become spendable after 100 blocks, and any<br>
transaction spending them can exist exclusively on one chain.<br></blockquo=
te><div><br></div><div>This is something that hadn&#39;t entered my mind wh=
en I made my assertions. At the moment I can&#39;t see any way to avoid thi=
s fact.</div><div><br></div><blockquote class=3D"gmail_quote" style=3D"marg=
in:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Also any transaction whos casual history extends from one of the above<br>
cases can exist only on one chain. This also means that someone who<br>
has single-chain coins (via a conflict or from coinbase outputs) can<br>
pay small amount to many users to get their wallets to consume them<br>
and make more of the transactions single chain only-- if they wanted<br>
the process to happen faster.<br></blockquote><div><br></div><div>Wallets c=
ould detect this and notify the user. Due to Gresham&#39;s Law, I&#39;ll ad=
mit the observation that these outputs would likely get spent in preference=
 (as they are less fungible), but whether the payee would be happy to accep=
t them is a different matter.</div><div><br></div><blockquote class=3D"gmai=
l_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left=
:1ex"><span class=3D"">
&gt; Miners will migrate to the bigger chain in search of higher profits du=
e to higher volume of fees<br>
<br>
</span>The migration remark is a considerable oversimplification. Imagine i=
f<br>
I released a version of the software programmed to reassign ownership<br>
of a million of the earliest created unmoved coins to me at block<br>
400k, and then after that I made transaction to pay 5 coin/block in<br>
fees. Would miners move to this chain?=C2=A0 It pays more in fees!<br></blo=
ckquote><div><br></div><div>Well in your example they wouldn&#39;t, because=
 they know that your version wouldn&#39;t be accepted by the economic major=
ity. But it&#39;s not as clear cut for the larger blocks case. They may mov=
e over gradually as they see the new chain gain acceptance, demonstrated by=
 the higher trading volume on it.=C2=A0</div></div><br></div></div>

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