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Date: Sat, 4 Jul 2015 18:58:46 +0100
Message-ID: <CAE-z3OXZDh=ww33Qr6yGxzm3rzquiP0LNo6yQzL1si+-dr3a_g@mail.gmail.com>
From: Tier Nolan <tier.nolan@gmail.com>
Cc: bitcoin-dev@lists.linuxfoundation.org
Content-Type: multipart/alternative; boundary=001a1140021690706f051a106c32
Subject: Re: [bitcoin-dev] Fork of invalid blocks due to BIP66 violations
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On Sat, Jul 4, 2015 at 5:01 PM, Justus Ranvier <
justus@openbitcoinprivacyproject.org> wrote:

> How do we know if a committed UTXO set is valid? If a majority of the
> hashing power is willing to extend an invalid branch, it's reasonable to
> assume they'd be willing to commit an invalid UTXO set as well.
>

You can prove that it wasn't updated correctly.

For each transaction, the UTXO tree root before and after is committed.

You show the root before, and the root after and show that the after root
is wrong.  You also need to include some merkle paths to prove the
transform.


> If items in the the proof tree are required to be sorted, then it's easy
> to proof that an item is missing.
>

Yes, you can mostly get short proofs for each step, but you have to make
sure your proofs are also provable.

It means going through everything that needs to be proved for a block to be
valid.

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">On Sat, Jul 4, 2015 at 5:01 PM, Justus Ranvier <span dir=3D"ltr">&lt;<a=
 href=3D"mailto:justus@openbitcoinprivacyproject.org" target=3D"_blank">jus=
tus@openbitcoinprivacyproject.org</a>&gt;</span> wrote:<br><blockquote clas=
s=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;pad=
ding-left:1ex"><span class=3D"">
</span>How do we know if a committed UTXO set is valid? If a majority of th=
e<br>
hashing power is willing to extend an invalid branch, it&#39;s reasonable t=
o<br>
assume they&#39;d be willing to commit an invalid UTXO set as well.<br></bl=
ockquote><div><br></div><div>You can prove that it wasn&#39;t updated corre=
ctly.<br><br></div><div>For each transaction, the UTXO tree root before and=
 after is committed.<br><br></div><div>You show the root before, and the ro=
ot after and show that the after root is wrong.=C2=A0 You also need to incl=
ude some merkle paths to prove the transform.<br></div><div>=C2=A0<br></div=
><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1=
px #ccc solid;padding-left:1ex"><span class=3D"">
</span>If items in the the proof tree are required to be sorted, then it=
9;s easy<br>
to proof that an item is missing.<br></blockquote><div><br></div><div>Yes, =
you can mostly get short proofs for each step, but you have to make sure yo=
ur proofs are also provable.<br><br></div><div>It means going through every=
thing that needs to be proved for a block to be valid.<br></div></div></div=
></div>

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