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From: Lucas Ontivero <lucasontivero@gmail.com>
Date: Tue, 23 May 2023 09:17:23 -0300
Message-ID: <CALHvQn29S2T=ehqGD1vCJQQuC0aD6rjUUPsb+n80EBPgc_G4JA@mail.gmail.com>
To: Ben Carman <benthecarman@live.com>, 
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Coinjoin with less steps using ALL|ANYONECANPAY
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Hi all,

In some coinjoin implementations inputs are registered first because in
that way, if the user fails or refuses to sign the transaction the input is
banned and denial of service is made a bit more expensive, in the sense
that an attacker needs more and more utxos to keep the attack going.

Your proposal can work if you find an alternative mechanism for mitigating
the DoS attacks or when DoS attacks are not a problem (I can imagine there
are scenarios where it is not really important).

Best

- Lucas


On Mon, May 22, 2023 at 7:53=E2=80=AFPM Ben Carman via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> The problem with using ALL|ANYONECANPAY is that you cannot verify
> beforehand that the other inputs are the inputs you want added to the
> transaction.
>
> Some examples of bad things that could happen:
>
>
>    - Coordinator adds its own inputs, you still get your outputs but
>    effectively paid fees for no privacy gain
>    - The inputs added could be paying at a lower fee rate than expected,
>    causing the tx to take longer than what you paid for
>    - Different input types or amount are added so you no longer have the
>    same uniformity across the inputs
>    - (if you care) An input from a sanctioned address is added, causing
>    you to get "tainted" coins.
>
> This is the code in ln-vortex that verifies the psbt on the client side i=
f
> you are curious
>
>
> https://github.com/ln-vortex/ln-vortex/blob/master/client/src/main/scala/=
com/lnvortex/client/VortexClient.scala#L616
>
>
> Best,
>
> benthecarman
>
> ------------------------------
> *From:* bitcoin-dev <bitcoin-dev-bounces@lists.linuxfoundation.org> on
> behalf of alicexbt via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org=
>
> *Sent:* Monday, May 22, 2023 7:51 AM
> *To:* Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
> *Subject:* [bitcoin-dev] Coinjoin with less steps using ALL|ANYONECANPAY
>
> Hi Bitcoin Developers,
>
> I recently experimented with different sighash flags, PSBTs and realized
> ALL|ANYONECANPAY could be used to reduce some steps in coinjoin.
>
> Steps:
>
> - Register outputs.
> - One user creates a signed PSBT with 1 input, all registered outputs and
> ALL|ANYONECANPAY sighash flag. Other participants keep adding their input=
s
> to PSBT.
> - Finalize and broadcast the transaction.
>
> Proof of Concept (Aice and Bob): https://gitlab.com/-/snippets/2542297
>
> Tx:
> https://mempool.space/testnet/tx/c6dd626591dca7e25bbd516f01b23171eb0f2b62=
3471fcf8e073c87c1179c492
>
> I plan to use this in joinstr if there are no major drawbacks and it can
> even be implemented by other coinjoin implementations.
>
> /dev/fd0
> floppy disk guy
>
> Sent with Proton Mail secure email.
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr"><div>Hi all,<br><br></div><div>In some coinjoin implementa=
tions inputs are registered first because in that way, if the user fails or=
 refuses to sign the transaction the input is banned and denial of service =
is made a bit more expensive, in the sense that an attacker needs more and =
more utxos to keep the attack going. <br></div><div><br></div><div>Your pro=
posal can work if you find an alternative mechanism for mitigating the DoS =
attacks or when DoS attacks are not a problem (I can imagine there are scen=
arios where it is not really important).<br><br></div><div>Best<br><br></di=
v><div>- Lucas<font style=3D"font-size:11pt;color:rgb(0,0,0)" face=3D"Calib=
ri, sans-serif"><br></font></div><div><br></div></div><br><div class=3D"gma=
il_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Mon, May 22, 2023 at 7:5=
3=E2=80=AFPM Ben Carman via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@l=
ists.linuxfoundation.org">bitcoin-dev@lists.linuxfoundation.org</a>&gt; wro=
te:<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"><div class=
=3D"msg3570622886445785554">




<div dir=3D"ltr">
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
The problem with using ALL|ANYONECANPAY is that you cannot verify beforehan=
d that the other inputs are the inputs you want added to the transaction.</=
div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
Some examples of bad things that could happen:</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<ul>
<li style=3D"list-style-type:&quot;- &quot;"><span>Coordinator adds its own=
 inputs, you still get your outputs but effectively paid fees for no privac=
y gain</span></li><li style=3D"list-style-type:&quot;- &quot;"><span>The in=
puts added could be paying at a lower fee rate than expected, causing the t=
x to take longer than what you paid for</span></li><li style=3D"list-style-=
type:&quot;- &quot;"><span>Different input types or amount are added so you=
 no longer have the same uniformity across the inputs</span></li><li style=
=3D"list-style-type:&quot;- &quot;"><span>(if you care) An input from a san=
ctioned address is added, causing you to get &quot;tainted&quot; coins.<br>
</span></li></ul>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
This is the code in ln-vortex that verifies the psbt on the client side if =
you are curious<br>
<br>
<a href=3D"https://github.com/ln-vortex/ln-vortex/blob/master/client/src/ma=
in/scala/com/lnvortex/client/VortexClient.scala#L616" id=3D"m_3570622886445=
785554LPNoLPOWALinkPreview" target=3D"_blank">https://github.com/ln-vortex/=
ln-vortex/blob/master/client/src/main/scala/com/lnvortex/client/VortexClien=
t.scala#L616</a>
<div></div>
<br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
Best,</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
benthecarman<br>
</div>
<div id=3D"m_3570622886445785554appendonsend"></div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color=
:rgb(0,0,0)">
<br>
</div>
<hr style=3D"display:inline-block;width:98%">
<div id=3D"m_3570622886445785554divRplyFwdMsg" dir=3D"ltr"><font style=3D"f=
ont-size:11pt;color:rgb(0,0,0)" face=3D"Calibri, sans-serif"><b>From:</b> b=
itcoin-dev &lt;<a href=3D"mailto:bitcoin-dev-bounces@lists.linuxfoundation.=
org" target=3D"_blank">bitcoin-dev-bounces@lists.linuxfoundation.org</a>&gt=
; on behalf of alicexbt via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@l=
ists.linuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.linuxfoundati=
on.org</a>&gt;<br>
<b>Sent:</b> Monday, May 22, 2023 7:51 AM<br>
<b>To:</b> Bitcoin Protocol Discussion &lt;<a href=3D"mailto:bitcoin-dev@li=
sts.linuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.linuxfoundatio=
n.org</a>&gt;<br>
<b>Subject:</b> [bitcoin-dev] Coinjoin with less steps using ALL|ANYONECANP=
AY</font>
<div>=C2=A0</div>
</div>
<div><font size=3D"2"><span style=3D"font-size:11pt">
<div>Hi Bitcoin Developers,<br>
<br>
I recently experimented with different sighash flags, PSBTs and realized AL=
L|ANYONECANPAY could be used to reduce some steps in coinjoin.<br>
<br>
Steps:<br>
<br>
- Register outputs.<br>
- One user creates a signed PSBT with 1 input, all registered outputs and A=
LL|ANYONECANPAY sighash flag. Other participants keep adding their inputs t=
o PSBT.<br>
- Finalize and broadcast the transaction.<br>
<br>
Proof of Concept (Aice and Bob):=C2=A0<a href=3D"https://gitlab.com/-/snipp=
ets/2542297" target=3D"_blank">https://gitlab.com/-/snippets/2542297</a><br=
>
<br>
Tx: <a href=3D"https://mempool.space/testnet/tx/c6dd626591dca7e25bbd516f01b=
23171eb0f2b623471fcf8e073c87c1179c492" target=3D"_blank">
https://mempool.space/testnet/tx/c6dd626591dca7e25bbd516f01b23171eb0f2b6234=
71fcf8e073c87c1179c492</a><br>
<br>
I plan to use this in joinstr if there are no major drawbacks and it can ev=
en be implemented by other coinjoin implementations.
<br>
<br>
/dev/fd0<br>
floppy disk guy<br>
<br>
Sent with Proton Mail secure email.<br>
_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
target=3D"_blank">https://lists.linuxfoundation.org/mailman/listinfo/bitcoi=
n-dev</a><br>
</div>
</span></font></div>
</div>

_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
</div></blockquote></div>

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