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From: Mike Hearn <mike@plan99.net>
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Subject: Re: [Bitcoin-development] Draft BIP for geutxos message
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I took the number out, it is now just "the getutxo bip" until a number is
assigned.


On Thu, Jul 10, 2014 at 4:29 PM, Mike Hearn <mike@plan99.net> wrote:

> I opened up a pull req for a draft BIP for getutxo.
>
>    https://github.com/bitcoin/bips/pull/88
>
> I include a rendering below for your reading convenience. If you'd like to
> comment on design/security/etc then please first familiarise yourself with
> the long discussions that were already had here:
>
>    https://github.com/bitcoin/bitcoin/pull/4351
>
>
>   BIP: 45
>   Title: getutxo message
>   Author: Mike Hearn <hearn@vinumeris.com>
>   Status: Draft
>   Type: Standards Track
>   Created: 2014-06-10
>
>  Table of Contents
>
>    - Abstract
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Abstract>
>       - Motivation
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Motivation>
>       - Specification
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Specification>
>       - Backward compatibility
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Backward_compatibility>
>       - Authentication
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Authentication>
>       - Implementation
>       <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#Implementation>
>
>
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#abstract>
> Abstract
>
> This document describes a small P2P protocol extension that performs UTXO
> lookups given a set of outpoints.
>
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#motivation>
> Motivation
>
> All full Bitcoin nodes maintain a database called the unspent transaction
> output set. This set is how double spending is checked for: to be valid a
> transaction must identify unspent outputs in this set using an identifier
> called an "outpoint", which is merely the hash of the output's containing
> transaction plus an index.
>
> The ability to query this can sometimes be useful for a lightweight/SPV
> client which does not have the full UTXO set at hand. For example, it can
> be useful in applications implementing assurance contracts to do a quick
> check when a new pledge becomes visible to test whether that pledge was
> already revoked via a double spend. Although this message is not strictly
> necessary because e.g. such an app could be implemented by fully
> downloading and storing the block chain, it is useful for obtaining
> acceptable performance and resolving various UI cases.
>
> Another example of when this data can be useful is for performing floating
> fee calculations in an SPV wallet. This use case requires some other
> changes to the Bitcoin protocol however, so we will not dwell on it here.
>
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#specification>
> Specification
>
> Two new messages are defined. The "getutxos" message has the following
> structure:
>
>  Field Size DescriptionData typeComments 1check mempoolbool Whether to
> apply mempool transactions during the calculation, thus exposing their
> UTXOs and removing outputs that they spend. ?outpointsvector The list of
> outpoints to be queried. Each outpoint is serialized in the same way it is
> in a tx message.
>
> The response message "utxos" has the following structure:
>
>  Field Size DescriptionData typeComments 4chain heightuint32 The height
> of the chain at the moment the result was calculated. 32chain tip hash
> uint256 Block hash of the top of the chain at the moment the result was
> calculated. ?hit bitmapbyte[] An array of bytes encoding one bit for each
> outpoint queried. Each bit indicates whether the queried outpoint was found
> in the UTXO set or not. ?result utxosresult[] A list of result objects
> (defined below), one for each outpoint that is unspent (i.e. has a bit set
> in the bitmap).
>
> The result object is defined as:
>
>  Field Size DescriptionData typeComments 4tx versionuint32 The version
> number of the transaction the UTXO was found in. 4heightuint256 The
> height of the block containing the defining transaction, or 0x7FFFFFFF if
> the tx is in the mempool. ?outputCTxOut The output itself, serialized in
> the same way as in a tx message.
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#backward-compatibility>Backward
> compatibility
>
> Nodes indicate support by advertising a protocol version above 70003 and
> by setting a new NODE_GETUTXO flag in their nServices field, which has a
> value of 2 (1
>
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#authentication>
> Authentication
>
> The UTXO set is not currently authenticated by anything. There are
> proposals to resolve this by introducing a new consensus rule that commits
> to a root hash of the UTXO set in blocks, however this feature is not
> presently available in the Bitcoin protocol. Once it is, the utxos message
> could be upgraded to include Merkle branches showing inclusion of the UTXOs
> in the committed sets.
>
> If the requesting client is looking up outputs for a signed transaction
> that they have locally, the client can partly verify the returned output by
> running the input scripts with it. Currently this verifies only that the
> script is correct. A future version of the Bitcoin protocol is likely to
> also allow the value to be checked in this way. It does not show that the
> output is really unspent or was ever actually created in the block chain
> however.
>
> If the requesting client has a mapping of chain heights to block hashes in
> the best chain e.g. obtained via getheaders, then they can obtain a proof
> that the output did at one point exist by requesting the block and
> searching for the output within it. When combined with Bloom filtering this
> can be reasonably efficient.
>
> Note that even when the outputs are being checked against something this
> protocol has the same security model as Bloom filtering: a remote node can
> lie through omission by claiming the requested UTXO does not exist / was
> already spent (they are the same, from the perspective of a full node).
> Querying multiple nodes and combining their answers can be a partial
> solution to this, although as nothing authenticates the Bitcoin P2P network
> a man in the middle could still yield incorrect results.
>
> <https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_path=35c7795#implementation>
> Implementation
>
> https://github.com/bitcoin/bitcoin/pull/4351/files
>

--e89a8ff1ce12abf25804fdd7db7b
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">I took the number out, it is now just &quot;the getutxo bi=
p&quot; until a number is assigned.</div><div class=3D"gmail_extra"><br><br=
><div class=3D"gmail_quote">On Thu, Jul 10, 2014 at 4:29 PM, Mike Hearn <sp=
an dir=3D"ltr">&lt;<a href=3D"mailto:mike@plan99.net" target=3D"_blank">mik=
e@plan99.net</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div>I opened up a pull req=
 for a draft BIP for getutxo.</div><div><br></div>=C2=A0 =C2=A0<a href=3D"h=
ttps://github.com/bitcoin/bips/pull/88" target=3D"_blank">https://github.co=
m/bitcoin/bips/pull/88</a><br>
<div><br></div><div>I include a rendering below for your reading convenienc=
e. If you&#39;d like to comment on design/security/etc then please first fa=
miliarise yourself with the long discussions that were already had here:</d=
iv>

<div><br></div><div>=C2=A0 =C2=A0<a href=3D"https://github.com/bitcoin/bitc=
oin/pull/4351" target=3D"_blank">https://github.com/bitcoin/bitcoin/pull/43=
51</a><br></div><div><br></div><div><br></div><div><pre style=3D"overflow:a=
uto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;=
font-size:13px;margin:15px auto;border:1px solid rgb(221,221,221);line-heig=
ht:19px;padding:10px 20px;border-top-left-radius:3px;border-top-right-radiu=
s:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wra=
p:normal;max-width:700px;color:rgb(51,51,51);background-color:rgb(248,248,2=
48)">
  BIP: 45
  Title: getutxo message
  Author: Mike Hearn &lt;<a href=3D"mailto:hearn@vinumeris.com" target=3D"_=
blank">hearn@vinumeris.com</a>&gt;
  Status: Draft
  Type: Standards Track
  Created: 2014-06-10
</pre><p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font=
-family:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,=
&#39;Segoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">

</p><table summary=3D"Contents" style=3D"border-collapse:collapse;border-sp=
acing:0px;margin:15px auto;width:700px;overflow:auto;display:block;max-widt=
h:700px;color:rgb(51,51,51);font-family:Helvetica,arial,freesans,clean,sans=
-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;li=
ne-height:27.200000762939453px">

<tbody><tr style=3D"border-top-width:1px;border-top-style:solid;border-top-=
color:rgb(204,204,204)"><td style=3D"padding:6px 13px;border:1px solid rgb(=
221,221,221)"><div>Table of Contents</div><ul style=3D"padding:0px 0px 0px =
30px;margin:15px 0px">

<ul style=3D"padding:0px 0px 0px 30px;margin:0px"><li><a href=3D"https://gi=
thub.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?sho=
rt_path=3D35c7795#Abstract" style=3D"color:rgb(65,131,196);text-decoration:=
none;background:transparent" target=3D"_blank">Abstract</a></li>

<li><a href=3D"https://github.com/mikehearn/bips/commit/6058b92f5d9804ee410=
4649f53afc2fa53248c81?short_path=3D35c7795#Motivation" style=3D"color:rgb(6=
5,131,196);text-decoration:none;background:transparent" target=3D"_blank">M=
otivation</a></li>
<li>
<a href=3D"https://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649=
f53afc2fa53248c81?short_path=3D35c7795#Specification" style=3D"color:rgb(65=
,131,196);text-decoration:none;background:transparent" target=3D"_blank">Sp=
ecification</a></li>

<li><a href=3D"https://github.com/mikehearn/bips/commit/6058b92f5d9804ee410=
4649f53afc2fa53248c81?short_path=3D35c7795#Backward_compatibility" style=3D=
"color:rgb(65,131,196);text-decoration:none;background:transparent" target=
=3D"_blank">Backward compatibility</a></li>

<li><a href=3D"https://github.com/mikehearn/bips/commit/6058b92f5d9804ee410=
4649f53afc2fa53248c81?short_path=3D35c7795#Authentication" style=3D"color:r=
gb(65,131,196);text-decoration:none;background:transparent" target=3D"_blan=
k">Authentication</a></li>

<li><a href=3D"https://github.com/mikehearn/bips/commit/6058b92f5d9804ee410=
4649f53afc2fa53248c81?short_path=3D35c7795#Implementation" style=3D"color:r=
gb(65,131,196);text-decoration:none;background:transparent" target=3D"_blan=
k">Implementation</a></li>

</ul></ul></td></tr></tbody></table><h2 style=3D"margin:15px auto;line-heig=
ht:1.7;font-size:2em;padding:0px;border-bottom-width:1px;border-bottom-styl=
e:solid;border-bottom-color:rgb(238,238,238);max-width:700px;color:rgb(51,5=
1,51);font-family:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI E=
moji&#39;,&#39;Segoe UI Symbol&#39;">

<a name=3D"14720ad957acd8bb_user-content-abstract" href=3D"https://github.c=
om/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_pat=
h=3D35c7795#abstract" style=3D"color:rgb(65,131,196);text-decoration:none;d=
isplay:block;padding-right:6px;padding-left:30px;background:transparent" ta=
rget=3D"_blank"></a><a name=3D"14720ad957acd8bb_user-content-Abstract" styl=
e=3D"color:rgb(65,131,196);background:transparent">Abstract</a></h2>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">This d=
ocument describes a small P2P protocol extension that performs UTXO lookups=
 given a set of outpoints.</p>

<h2 style=3D"margin:15px auto;line-height:1.7;font-size:2em;padding:0px;bor=
der-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,=
238,238);max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,fr=
eesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;"=
>

<a name=3D"14720ad957acd8bb_user-content-motivation" href=3D"https://github=
.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?short_p=
ath=3D35c7795#motivation" style=3D"color:rgb(65,131,196);text-decoration:no=
ne;display:block;padding-right:6px;padding-left:30px;background:transparent=
" target=3D"_blank"></a><a name=3D"14720ad957acd8bb_user-content-Motivation=
" style=3D"color:rgb(65,131,196);background:transparent">Motivation</a></h2=
>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">All fu=
ll Bitcoin nodes maintain a database called the unspent transaction output =
set. This set is how double spending is checked for: to be valid a transact=
ion must identify unspent outputs in this set using an identifier called an=
 &quot;outpoint&quot;, which is merely the hash of the output&#39;s contain=
ing transaction plus an index.</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">The ab=
ility to query this can sometimes be useful for a lightweight/SPV client wh=
ich does not have the full UTXO set at hand. For example, it can be useful =
in applications implementing assurance contracts to do a quick check when a=
 new pledge becomes visible to test whether that pledge was already revoked=
 via a double spend. Although this message is not strictly necessary becaus=
e e.g. such an app could be implemented by fully downloading and storing th=
e block chain, it is useful for obtaining acceptable performance and resolv=
ing various UI cases.</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">Anothe=
r example of when this data can be useful is for performing floating fee ca=
lculations in an SPV wallet. This use case requires some other changes to t=
he Bitcoin protocol however, so we will not dwell on it here.</p>

<h2 style=3D"margin:15px auto;line-height:1.7;font-size:2em;padding:0px;bor=
der-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,=
238,238);max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,fr=
eesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;"=
>

<a name=3D"14720ad957acd8bb_user-content-specification" href=3D"https://git=
hub.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?shor=
t_path=3D35c7795#specification" style=3D"color:rgb(65,131,196);text-decorat=
ion:none;display:block;padding-right:6px;padding-left:30px;background:trans=
parent" target=3D"_blank"></a><a name=3D"14720ad957acd8bb_user-content-Spec=
ification" style=3D"color:rgb(65,131,196);background:transparent">Specifica=
tion</a></h2>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">Two ne=
w messages are defined. The &quot;getutxos&quot; message has the following =
structure:</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px"></p>

<table style=3D"border-collapse:collapse;border-spacing:0px;margin:15px aut=
o;width:700px;overflow:auto;display:block;max-width:700px;color:rgb(51,51,5=
1);font-family:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoj=
i&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939=
453px">

<tbody><tr style=3D"border-top-width:1px;border-top-style:solid;border-top-=
color:rgb(204,204,204)"><th style=3D"padding:6px 13px;border:1px solid rgb(=
221,221,221)">Field Size</th><th style=3D"padding:6px 13px;border:1px solid=
 rgb(221,221,221)">

Description</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,221,=
221)">Data type</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,=
221,221)">Comments</th></tr><tr style=3D"border-top-width:1px;border-top-st=
yle:solid;border-top-color:rgb(204,204,204);background-color:rgb(248,248,24=
8)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">1</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">check mempool<=
/td><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">bool</=
td>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">Whether to=
 apply mempool transactions during the calculation, thus exposing their UTX=
Os and removing outputs that they spend.</td></tr><tr style=3D"border-top-w=
idth:1px;border-top-style:solid;border-top-color:rgb(204,204,204)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">?</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">outpoints</td>=
<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">vector</td=
>
<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">
The list of outpoints to be queried. Each outpoint is serialized in the sam=
e way it is in a tx message.</td></tr></tbody></table><p style=3D"margin:15=
px auto;max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,fre=
esans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;f=
ont-size:16px;line-height:27.200000762939453px">

The response message &quot;utxos&quot; has the following structure:</p><p s=
tyle=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-family:He=
lvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe=
 UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">

</p><table style=3D"border-collapse:collapse;border-spacing:0px;margin:15px=
 auto;width:700px;overflow:auto;display:block;max-width:700px;color:rgb(51,=
51,51);font-family:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI =
Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;line-height:27.20000076=
2939453px">

<tbody><tr style=3D"border-top-width:1px;border-top-style:solid;border-top-=
color:rgb(204,204,204)"><th style=3D"padding:6px 13px;border:1px solid rgb(=
221,221,221)">Field Size</th><th style=3D"padding:6px 13px;border:1px solid=
 rgb(221,221,221)">

Description</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,221,=
221)">Data type</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,=
221,221)">Comments</th></tr><tr style=3D"border-top-width:1px;border-top-st=
yle:solid;border-top-color:rgb(204,204,204);background-color:rgb(248,248,24=
8)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">4</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">chain height</=
td><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">uint32<=
/td>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">The height=
 of the chain at the moment the result was calculated.</td></tr><tr style=
=3D"border-top-width:1px;border-top-style:solid;border-top-color:rgb(204,20=
4,204)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">32</td><td=
 style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">chain tip has=
h</td><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">uint=
256</td>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">Block hash=
 of the top of the chain at the moment the result was calculated.</td></tr>=
<tr style=3D"border-top-width:1px;border-top-style:solid;border-top-color:r=
gb(204,204,204);background-color:rgb(248,248,248)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">?</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">hit bitmap</td=
><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">byte[]</t=
d>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">An array o=
f bytes encoding one bit for each outpoint queried. Each bit indicates whet=
her the queried outpoint was found in the UTXO set or not.</td></tr><tr sty=
le=3D"border-top-width:1px;border-top-style:solid;border-top-color:rgb(204,=
204,204)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">?</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">result utxos</=
td><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">result[=
]</td>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">A list of =
result objects (defined below), one for each outpoint that is unspent (i.e.=
 has a bit set in the bitmap).</td></tr></tbody></table><p style=3D"margin:=
15px auto;max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,f=
reesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;=
;font-size:16px;line-height:27.200000762939453px">

The result object is defined as:</p><p style=3D"margin:15px auto;max-width:=
700px;color:rgb(51,51,51);font-family:Helvetica,arial,freesans,clean,sans-s=
erif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;line=
-height:27.200000762939453px">

</p><table style=3D"border-collapse:collapse;border-spacing:0px;margin:15px=
 auto;width:700px;overflow:auto;display:block;max-width:700px;color:rgb(51,=
51,51);font-family:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI =
Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;line-height:27.20000076=
2939453px">

<tbody><tr style=3D"border-top-width:1px;border-top-style:solid;border-top-=
color:rgb(204,204,204)"><th style=3D"padding:6px 13px;border:1px solid rgb(=
221,221,221)">Field Size</th><th style=3D"padding:6px 13px;border:1px solid=
 rgb(221,221,221)">

Description</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,221,=
221)">Data type</th><th style=3D"padding:6px 13px;border:1px solid rgb(221,=
221,221)">Comments</th></tr><tr style=3D"border-top-width:1px;border-top-st=
yle:solid;border-top-color:rgb(204,204,204);background-color:rgb(248,248,24=
8)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">4</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">tx version</td=
><td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">uint32</t=
d>

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">The versio=
n number of the transaction the UTXO was found in.</td></tr><tr style=3D"bo=
rder-top-width:1px;border-top-style:solid;border-top-color:rgb(204,204,204)=
">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">4</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">height</td><td=
 style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">uint256</td><=
td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">

The height of the block containing the defining transaction, or 0x7FFFFFFF =
if the tx is in the mempool.</td></tr><tr style=3D"border-top-width:1px;bor=
der-top-style:solid;border-top-color:rgb(204,204,204);background-color:rgb(=
248,248,248)">

<td style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">?</td><td =
style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">output</td><td=
 style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">CTxOut</td><t=
d style=3D"padding:6px 13px;border:1px solid rgb(221,221,221)">

The output itself, serialized in the same way as in a tx message.</td></tr>=
</tbody></table><h2 style=3D"margin:15px auto;line-height:1.7;font-size:2em=
;padding:0px;border-bottom-width:1px;border-bottom-style:solid;border-botto=
m-color:rgb(238,238,238);max-width:700px;color:rgb(51,51,51);font-family:He=
lvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe=
 UI Symbol&#39;">

<a name=3D"14720ad957acd8bb_user-content-backward-compatibility" href=3D"ht=
tps://github.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa5324=
8c81?short_path=3D35c7795#backward-compatibility" style=3D"color:rgb(65,131=
,196);text-decoration:none;display:block;padding-right:6px;padding-left:30p=
x;background:transparent" target=3D"_blank"></a><a name=3D"14720ad957acd8bb=
_user-content-Backward_compatibility" style=3D"color:rgb(65,131,196);backgr=
ound:transparent">Backward compatibility</a></h2>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">Nodes =
indicate support by advertising a protocol version above 70003 and by setti=
ng a new NODE_GETUTXO flag in their nServices field, which has a value of 2=
 (1</p>

<h2 style=3D"margin:15px auto;line-height:1.7;font-size:2em;padding:0px;bor=
der-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,=
238,238);max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,fr=
eesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;"=
>

<a name=3D"14720ad957acd8bb_user-content-authentication" href=3D"https://gi=
thub.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?sho=
rt_path=3D35c7795#authentication" style=3D"color:rgb(65,131,196);text-decor=
ation:none;display:block;padding-right:6px;padding-left:30px;background:tra=
nsparent" target=3D"_blank"></a><a name=3D"14720ad957acd8bb_user-content-Au=
thentication" style=3D"color:rgb(65,131,196);background:transparent">Authen=
tication</a></h2>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">The UT=
XO set is not currently authenticated by anything. There are proposals to r=
esolve this by introducing a new consensus rule that commits to a root hash=
 of the UTXO set in blocks, however this feature is not presently available=
 in the Bitcoin protocol. Once it is, the utxos message could be upgraded t=
o include Merkle branches showing inclusion of the UTXOs in the committed s=
ets.</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">If the=
 requesting client is looking up outputs for a signed transaction that they=
 have locally, the client can partly verify the returned output by running =
the input scripts with it. Currently this verifies only that the script is =
correct. A future version of the Bitcoin protocol is likely to also allow t=
he value to be checked in this way. It does not show that the output is rea=
lly unspent or was ever actually created in the block chain however.</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">If the=
 requesting client has a mapping of chain heights to block hashes in the be=
st chain e.g. obtained via getheaders, then they can obtain a proof that th=
e output did at one point exist by requesting the block and searching for t=
he output within it. When combined with Bloom filtering this can be reasona=
bly efficient.</p>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px">Note t=
hat even when the outputs are being checked against something this protocol=
 has the same security model as Bloom filtering: a remote node can lie thro=
ugh omission by claiming the requested UTXO does not exist / was already sp=
ent (they are the same, from the perspective of a full node). Querying mult=
iple nodes and combining their answers can be a partial solution to this, a=
lthough as nothing authenticates the Bitcoin P2P network a man in the middl=
e could still yield incorrect results.</p>

<h2 style=3D"margin:15px auto;line-height:1.7;font-size:2em;padding:0px;bor=
der-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,=
238,238);max-width:700px;color:rgb(51,51,51);font-family:Helvetica,arial,fr=
eesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;"=
>

<a name=3D"14720ad957acd8bb_user-content-implementation" href=3D"https://gi=
thub.com/mikehearn/bips/commit/6058b92f5d9804ee4104649f53afc2fa53248c81?sho=
rt_path=3D35c7795#implementation" style=3D"color:rgb(65,131,196);text-decor=
ation:none;display:block;padding-right:6px;padding-left:30px;background:tra=
nsparent" target=3D"_blank"></a><a name=3D"14720ad957acd8bb_user-content-Im=
plementation" style=3D"color:rgb(65,131,196);background:transparent">Implem=
entation</a></h2>

<p style=3D"margin:15px auto;max-width:700px;color:rgb(51,51,51);font-famil=
y:Helvetica,arial,freesans,clean,sans-serif,&#39;Segoe UI Emoji&#39;,&#39;S=
egoe UI Symbol&#39;;font-size:16px;line-height:27.200000762939453px"><a hre=
f=3D"https://github.com/bitcoin/bitcoin/pull/4351/files" style=3D"color:rgb=
(65,131,196);text-decoration:none;background:transparent" target=3D"_blank"=
>https://github.com/bitcoin/bitcoin/pull/4351/files</a></p>

</div></div>
</blockquote></div><br></div>

--e89a8ff1ce12abf25804fdd7db7b--