From: Damian Williamson <willtech@live.com.au>
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Thread-Topic: [bitcoin-dev] Sign / Verify message against SegWit P2SH and
	Bech32 addresses
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Date: Tue, 13 Mar 2018 13:26:17 +0000
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Subject: [bitcoin-dev] Sign / Verify message against SegWit P2SH and Bech32
 addresses
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Current implementation of sign/verify is broken for SegWit and Bech32 addre=
sses.


Please add the following reference to the use cases:

---

# Does blockchain.info show balances for addresses that are in cold storage=
?

Yes.

>... is there any way for me in another country to confirm that what my col=
league views is actually accurate and correct?

Since they use Bitcoin Core, yes, there is a way to verify that they hold t=
he addresses that they claim. Have them sign a message with each address th=
at they claim to have the holdings on, using Bitcoin Core you can verify th=
at they indeed have those addresses and check them on blockchain.info to fi=
nd the current balance.

Only works in Bitcoin Core currently for addresses starting with a '1' (not=
 Segwit addresses starting with a '3' and not Bech32 addresses starting wit=
h 'bc1' - the developers are aware of this and I will remind them shortly.)

In Bitcoin Core, your transaction opposite goes to File -> Sign Message and=
 signs any message with one of the holding addresses. Copy the message, add=
ress and signature and send to you via probably plain text format email is =
the easiest. Repeat for each additional address holding the balance of BTC =
that they are offering to sell.

In Bitcoin Core, you go to File -> Verify Message and key the details provi=
ded EXACTLY - spaces, new lines and all characters must be an EXACT match. =
Click on verify and voil=E0.

I prefer the form of signed message as follows (don't key the top and botto=
m bar rows for the message, just the contents and you can check this yourse=
lf, the bottom row is the signature). I like to key the address used for ve=
rifying as a part of the message but that is not strictly necessary:

    ------------------------------
    Something that I want to sign.

    bitcoin:1PMUf9aaQ41M4bgVbCAPVwAeuKvj8CwxJg
    ------------------------------
    Signture:
    IGaXlQNRHHM6ferJ+Ocr3cN9dRJhIWxo+n9PGwgg1uPdOLVYIeCuaccEzDygVgYPJMXqmQe=
SaLaZVoG6FMHPJkg=3D

This contains all of the compact information necessary to verify the messag=
e.

Example of verified message:
![verified message][1]

[1]: https://i.stack.imgur.com/zv1xq.png

---

https://bitcoin.stackexchange.com/a/72281/75001



Solution seems to be straight-forward, as noted in Issue# [10542](https://g=
ithub.com/bitcoin/bitcoin/issues/10542#issuecomment-306584383)


>And it would in theory be possible to make signmessage work for a P2SH-P2W=
PKH address, in cases where the verifier knows the embedded pubkeyhash alre=
ady. But in that case you don't need "sign with a witness address" function=
ality - *you could just sign with the embedded key (see validateaddress), a=
nd have the verifier check that*.


>The point is to not further the misunderstanding that signmessage signs wi=
th an address - it never did. It signs with a keyhash, and verify with a ke=
yhash.


This is an important feature, there are few other ways to verify that an ad=
dress is held. Note that the linked issue is not currently labeld GUI and p=
robably could be - unless a new issue should also be opened?


Regards,

Damian Williamson


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<head>
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1">
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n-bottom:0;} --></style>
</head>
<body dir=3D"ltr">
<div id=3D"divtagdefaultwrapper" style=3D"font-size:12pt;color:#000000;font=
-family:Calibri,Helvetica,sans-serif;" dir=3D"ltr">
<p style=3D"margin-top:0;margin-bottom:0">Current implementation of sign/ve=
rify is broken for SegWit and Bech32 addresses.</p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p style=3D"margin-top:0;margin-bottom:0">Please add the following referenc=
e to the use cases:</p>
<p style=3D"margin-top:0;margin-bottom:0">---<br>
</p>
<p style=3D"margin-top:0;margin-bottom:0"></p>
<div>
<div># Does blockchain.info show balances for addresses that are in cold st=
orage?<br>
<br>
Yes.<br>
<br>
&gt;... is there any way for me in another country to confirm that what my =
colleague views is actually accurate and correct?<br>
<br>
Since they use Bitcoin Core, yes, there is a way to verify that they hold t=
he addresses that they claim. Have them sign a message with each address th=
at they claim to have the holdings on, using Bitcoin Core you can verify th=
at they indeed have those addresses
 and check them on blockchain.info to find the current balance.<br>
<br>
Only works in Bitcoin Core currently for addresses starting with a '1' (not=
 Segwit addresses starting with a '3' and not Bech32 addresses starting wit=
h 'bc1' - the developers are aware of this and I will remind them shortly.)=
<br>
<br>
In Bitcoin Core, your transaction opposite goes to File -&gt; Sign Message =
and signs any message with one of the holding addresses. Copy the message, =
address and signature and send to you via probably plain text format email =
is the easiest. Repeat for each additional
 address holding the balance of BTC that they are offering to sell.<br>
<br>
In Bitcoin Core, you go to File -&gt; Verify Message and key the details pr=
ovided EXACTLY - spaces, new lines and all characters must be an EXACT matc=
h. Click on verify and voil=E0.<br>
<br>
I prefer the form of signed message as follows (don't key the top and botto=
m bar rows for the message, just the contents and you can check this yourse=
lf, the bottom row is the signature). I like to key the address used for ve=
rifying as a part of the message
 but that is not strictly necessary:<br>
<br>
&nbsp;&nbsp;&nbsp; ------------------------------<br>
&nbsp;&nbsp;&nbsp; Something that I want to sign.<br>
&nbsp;&nbsp; &nbsp;<br>
&nbsp;&nbsp;&nbsp; bitcoin:1PMUf9aaQ41M4bgVbCAPVwAeuKvj8CwxJg<br>
&nbsp;&nbsp;&nbsp; ------------------------------<br>
&nbsp;&nbsp;&nbsp; Signture:<br>
&nbsp;&nbsp;&nbsp; IGaXlQNRHHM6ferJ&#43;Ocr3cN9dRJhIWxo&#43;n9PGwgg1uPdOLVY=
IeCuaccEzDygVgYPJMXqmQeSaLaZVoG6FMHPJkg=3D<br>
<br>
This contains all of the compact information necessary to verify the messag=
e.<br>
<br>
Example of verified message: &nbsp;<br>
![verified message][1]<br>
<br>
[1]: https://i.stack.imgur.com/zv1xq.png <br>
</div>
</div>
<p style=3D"margin-top:0;margin-bottom:0">---</p>
<p style=3D"margin-top:0;margin-bottom:0"><a href=3D"https://bitcoin.stacke=
xchange.com/a/72281/75001" class=3D"OWAAutoLink" id=3D"LPlnk231610" preview=
removed=3D"true">https://bitcoin.stackexchange.com/a/72281/75001</a></p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p></p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p style=3D"margin-top:0;margin-bottom:0">Solution seems to be straight-for=
ward, as noted in Issue# [10542](<a href=3D"https://github.com/bitcoin/bitc=
oin/issues/10542#issuecomment-306584383" class=3D"OWAAutoLink" id=3D"LPlnk6=
23905" previewremoved=3D"true">https://github.com/bitcoin/bitcoin/issues/10=
542#issuecomment-306584383</a>)</p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p style=3D"margin-top:0;margin-bottom:0">&gt;And it would in theory be pos=
sible to make
<code>signmessage</code> work for a P2SH-P2WPKH address, in cases where the=
 verifier knows the embedded pubkeyhash already. But in that case you don't=
 need &quot;sign with a witness address&quot; functionality - *you could ju=
st sign with the embedded key (see
<code>validateaddress</code>), and have the verifier check that*.</p>
<p><br>
</p>
<p>&gt;The point is to not further the misunderstanding that <code>signmess=
age</code> signs with an address - it never did. It signs with a keyhash, a=
nd verify with a keyhash.</p>
<p><br>
</p>
<p>This is an important feature, there are few other ways to verify that an=
 address is held. Note that the linked issue is not currently labeld GUI an=
d probably could be - unless a new issue should also be opened?</p>
<p><br>
</p>
<p>Regards,</p>
<p>Damian Williamson<br>
</p>
<br>
<p></p>
</div>
</body>
</html>

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