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In-Reply-To: <93649df9-27ab-abaf-00f3-da6c528344cc@purse.io>
From: Tier Nolan <tier.nolan@gmail.com>
Date: Tue, 15 Oct 2019 19:30:58 +0100
Message-ID: <CAE-z3OWRv1aw4_meRRon+5OA1rxerTr9=0DLWC5d7Xhyg8veBQ@mail.gmail.com>
To: Braydon Fuller via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="000000000000ad0d030594f7316c"
Subject: Re: [bitcoin-dev] Chain width expansion
Precedence: list

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On Tue, Oct 15, 2019 at 7:29 AM Braydon Fuller via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> So I don't think you can use the height in the coinbase for that
> purpose, as it's not possible to validate it without the previous
> headers. That's common for more than just the height.
>

It is a property of blockchains that the lowest digest for a chain
represents the total chainwork.

Estimate total hash count = N * (2^256) / (Nth lowest (i.e. strongest)
digest over all headers)

To produce a fake set of 10 headers that give a higher work estimate than
the main chain would require around the same effort as went into the main
chain in the first place.  You might as well completely build an
alternative chain.

Working backwards for one of those headers, you have to follow the actual
chain back to genesis.

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<div dir=3D"ltr"><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail=
_attr">On Tue, Oct 15, 2019 at 7:29 AM Braydon Fuller via bitcoin-dev &lt;<=
a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.l=
inuxfoundation.org</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote=
" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);=
padding-left:1ex">
So I don&#39;t think you can use the height in the coinbase for that<br>
purpose, as it&#39;s not possible to validate it without the previous<br>
headers. That&#39;s common for more than just the height.<br></blockquote><=
div><br></div><div>It is a property of blockchains that the lowest digest f=
or a chain represents the total chainwork.</div><div><br></div><div>Estimat=
e total hash count =3D N * (2^256) / (Nth lowest (i.e. strongest) digest ov=
er all headers)<br></div><div><br></div><div>To produce a fake set of 10 he=
aders that give a higher work estimate than the main chain would require ar=
ound the same effort as went into the main chain in the first place.=C2=A0 =
You might as well completely build an alternative chain.<br></div><div><br>=
</div><div>Working backwards for one of those headers, you have to follow t=
he actual chain back to genesis.</div></div></div>

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