From: "Kenshiro []" <tensiam@hotmail.com>
To: "bitcoin-dev@lists.linuxfoundation.org"
	<bitcoin-dev@lists.linuxfoundation.org>
Thread-Topic: Payjoin privacy with the receiver of the transaction
Thread-Index: AQHU3Xi3TuLQzioN20KrtFTwOE2knQ==
Date: Mon, 18 Mar 2019 10:55:34 +0000
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Subject: [bitcoin-dev] Payjoin privacy with the receiver of the transaction
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Hi,

I think Payjoin can be a very good privacy solution for Bitcoin, but I have=
 a question about it:

- If a user has 1 BTC in a single address and make a payjoin payment to oth=
er person of 0.1 BTC using that address as input, the other person can see =
in a blockchain explorer the change address with an amount of 0.9 BTC. That=
's a serious privacy leak. I would like to know what will be the standard s=
olution to this issue. An easy fix could be that the user wallet check if a=
ny address contains a BTC amount higher than a "safe" amount like 0.01 BTC =
or less. If some address exceed that amount the wallet could automatically =
make 1 payment to itself to split the amount in several addresses. In this =
way nobody receiving a payment from a user will ever know that he has a bit=
coin balance higher than the "safe" amount.

What do you think?

Regards,

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<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Diso-8859-=
1">
<style type=3D"text/css" style=3D"display:none;"> P {margin-top:0;margin-bo=
ttom:0;} </style>
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<body dir=3D"ltr">
<div style=3D"font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;=
 color: rgb(0, 0, 0);">
<span>Hi,<br>
</span>
<div><br>
</div>
<div>I think Payjoin can be a very good privacy solution for Bitcoin, but I=
 have a question about it:<br>
</div>
<div><br>
</div>
<div>- If a user has 1 BTC in a single address and make a payjoin payment t=
o other person of 0.1 BTC using that address as input, the other person can=
 see in a blockchain explorer the change address with an amount of 0.9 BTC.=
 That's a serious privacy leak.
 I would like to know what will be the standard solution to this issue. An =
easy fix could be that the user wallet check if any address contains a BTC =
amount higher than a &quot;safe&quot; amount like 0.01 BTC or less. If some=
 address exceed that amount the wallet could
 automatically make 1 payment to itself to split the amount in several addr=
esses. In this way nobody receiving a payment from a user will ever know th=
at he has a bitcoin balance higher than the &quot;safe&quot; amount.<br>
</div>
<div><br>
</div>
<div>What do you think?<br>
</div>
<div><br>
</div>
<span>Regards,</span><br>
</div>
</body>
</html>

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