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From: "Kenshiro []" <tensiam@hotmail.com>
To: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	"rhavar@protonmail.com" <rhavar@protonmail.com>
Thread-Topic: [bitcoin-dev] Payjoin privacy with the receiver of the
	transaction
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Date: Fri, 22 Mar 2019 10:23:24 +0000
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Subject: Re: [bitcoin-dev] Payjoin privacy with the receiver of the
 transaction
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>I'm not really sure the problem you're describing, but it sounds like some=
thing that affects normal bitcoin transactions as well.

Yeah, it affects normal transactions too. But I'm focused in Payjoin becaus=
e it should allow private transactions. The problem I see is that Payjoin s=
houldn't allow that the sender or the receiver of the transaction can get i=
nformation about the bitcoin balance of each other. A person could have his=
 savings in btc in a single address, use Payjoin to send/receive a payment =
thinking it's private and leaking to the receptor he has a high amount of b=
tc. But an automatic splitting to itself in the background could solve the =
problem (maybe 100$ amounts) or so.

>There's certainly some interesting about the idea of "pre-fragmenting" you=
r wallet utxo so you can make (or in payjoin: receive) payments with better=
 privacy aspects.However, it's pretty unlikely to be practical for normal u=
sers, as it'll generally result in pretty big and cost-ineffective transact=
ions.

For users that really want privacy it should not be a problem. When a walle=
t receive a high amount of btc (+100$ or another amount defined by the user=
) it can automatically make a transaction to itself splitting the amount in=
 several addresses. The amounts that are already small don't need to be spl=
itted again. Small amount addresses + Payjoin could give real privacy to bi=
tcoin users. Users that don't want privacy could disable the "Private" mode=
 in the wallet and disable the auto-splitting feature.

i.e.: you receive 1000$ in btc and the wallet make an automatic transaction=
 to itself to 10 addresses, 100$ each.

I would prefer wait some time and have privacy than the opposite.

Regards

________________________________
From: rhavar@protonmail.com <rhavar@protonmail.com>
Sent: Thursday, March 21, 2019 17:52
To: Kenshiro \[\]; Bitcoin Protocol Discussion
Subject: Re: [bitcoin-dev] Payjoin privacy with the receiver of the transac=
tion

I'm not really sure the problem you're describing, but it sounds like somet=
hing that affects normal bitcoin transactions as well.

There's certainly some interesting about the idea of "pre-fragmenting" your=
 wallet utxo so you can make (or in payjoin: receive) payments with better =
privacy aspects.However, it's pretty unlikely to be practical for normal us=
ers, as it'll generally result in pretty big and cost-ineffective transacti=
ons.

In general though, there's like a 1000 different things you can do with coi=
n selection, utxo management (and payjoin contributed input selection) but =
more often than not you are just making just making 1 trade off for another=
 and good solutions will be wildly different depending on how you use your =
wallet.


-Ryan


=1B$B!>!>!>!>!>!>!>=1B(B Original Message =1B$B!>!>!>!>!>!>!>=1B(B
On Monday, March 18, 2019 3:55 AM, Kenshiro \[\] via bitcoin-dev <bitcoin-d=
ev@lists.linuxfoundation.org> wrote:

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,


--_000_DB6PR10MB1832829D9C812F50C66BD11CA6430DB6PR10MB1832EURP_
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<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Diso-2022-=
jp">
<style type=3D"text/css" style=3D"display:none;"> P {margin-top:0;margin-bo=
ttom:0;} </style>
</head>
<body dir=3D"ltr">
<div style=3D"font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;=
 color: rgb(0, 0, 0);">
<span style=3D"color: rgb(51, 51, 51); font-family: &quot;Segoe UI&quot;, &=
quot;Segoe UI Web (West European)&quot;, &quot;Segoe UI&quot;, -apple-syste=
m, BlinkMacSystemFont, Roboto, &quot;Helvetica Neue&quot;, sans-serif; back=
ground-color: rgb(255, 255, 255); display: inline !important">&gt;I'm not r=
eally
 sure the problem you're describing, but it sounds like something that affe=
cts normal bitcoin transactions as well.</span><br>
</div>
<div style=3D"font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;=
 color: rgb(0, 0, 0);">
<span style=3D"color: rgb(51, 51, 51); font-family: &quot;Segoe UI&quot;, &=
quot;Segoe UI Web (West European)&quot;, &quot;Segoe UI&quot;, -apple-syste=
m, BlinkMacSystemFont, Roboto, &quot;Helvetica Neue&quot;, sans-serif; back=
ground-color: rgb(255, 255, 255); display: inline !important"><br>
</span></div>
<div style=3D"font-size: 12pt;">Yeah, it affects normal transactions too. B=
ut I'm focused in Payjoin because it should allow private transactions. The=
 problem I see is that Payjoin shouldn't allow that the sender or the recei=
ver of the transaction can get information
 about the bitcoin balance of each other. A person could have his savings i=
n btc in a single address, use Payjoin to send/receive a payment thinking i=
t's private and leaking to the receptor he has a high amount of btc. But an=
 automatic splitting to itself in
 the background could solve the problem (maybe 100$ amounts) or so.&nbsp;</=
div>
<div style=3D"font-size: 12pt;"><br>
</div>
<div style=3D"font-size: 12pt;"><span style=3D"font-family: &quot;Segoe UI&=
quot;, &quot;Segoe UI Web (West European)&quot;, &quot;Segoe UI&quot;, -app=
le-system, BlinkMacSystemFont, Roboto, &quot;Helvetica Neue&quot;, sans-ser=
if; background-color: rgb(255, 255, 255); display: inline !important">&gt;T=
here's
 certainly some interesting about the idea of &quot;pre-fragmenting&quot; y=
our wallet utxo so you can make (or in payjoin: receive) payments with bett=
er privacy aspects.However, it's pretty unlikely to be practical for normal=
 users, as it'll generally result in pretty
 big and cost-ineffective transactions.</span><br>
</div>
<div style=3D"font-size: 12pt;"><span style=3D"font-family: &quot;Segoe UI&=
quot;, &quot;Segoe UI Web (West European)&quot;, &quot;Segoe UI&quot;, -app=
le-system, BlinkMacSystemFont, Roboto, &quot;Helvetica Neue&quot;, sans-ser=
if; background-color: rgb(255, 255, 255); display: inline !important"><br>
</span></div>
<div style=3D"font-size: 12pt;">For users that really want privacy it shoul=
d not be a problem. When a wallet receive a high amount of btc (&#43;100$ o=
r another amount defined by the user) it can automatically make a transacti=
on to itself splitting the amount in several
 addresses. The amounts that are already small don't need to be splitted ag=
ain. Small amount addresses &#43; Payjoin could give real privacy to bitcoi=
n users. Users that don't want privacy could disable the &quot;Private&quot=
; mode in the wallet and disable the auto-splitting
 feature.&nbsp;</div>
<div style=3D"font-size: 12pt;"><br>
</div>
<div style=3D"font-size: 12pt;">i.e.: you receive 1000$ in btc and the wall=
et make an automatic transaction to itself to 10 addresses, 100$ each.</div=
>
<div style=3D"font-size: 12pt;"><br>
</div>
<div style=3D"font-size: 12pt;">I would prefer wait some time and have priv=
acy than the opposite.</div>
<div style=3D"font-size: 12pt;"><br>
</div>
<div style=3D"font-size: 12pt;">Regards</div>
<div>
<div id=3D"appendonsend"></div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif; font-size:12pt; col=
or:rgb(0,0,0)">
<br>
</div>
<hr tabindex=3D"-1" style=3D"display:inline-block; width:98%">
<div id=3D"divRplyFwdMsg" dir=3D"ltr"><font face=3D"Calibri, sans-serif" co=
lor=3D"#000000" style=3D"font-size:11pt"><b>From:</b> rhavar@protonmail.com=
 &lt;rhavar@protonmail.com&gt;<br>
<b>Sent:</b> Thursday, March 21, 2019 17:52<br>
<b>To:</b> Kenshiro \[\]; Bitcoin Protocol Discussion<br>
<b>Subject:</b> Re: [bitcoin-dev] Payjoin privacy with the receiver of the =
transaction</font>
<div>&nbsp;</div>
</div>
<div>
<div>I'm not really sure the problem you're describing, but it sounds like =
something that affects normal bitcoin transactions as well.<br>
</div>
<div><br>
</div>
<div>There's certainly some interesting about the idea of &quot;pre-fragmen=
ting&quot; your wallet utxo so you can make (or in payjoin: receive) paymen=
ts with better privacy aspects.However, it's pretty unlikely to be practica=
l for normal users, as it'll generally result
 in pretty big and cost-ineffective transactions.<br>
</div>
<div><br>
</div>
<div>In general though, there's like a 1000 different things you can do wit=
h coin selection, utxo management (and payjoin contributed input selection)=
 but more often than not you are just making just making 1 trade off for an=
other and good solutions will be
 wildly different depending on how you use your wallet.<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div class=3D"x_protonmail_signature_block">
<div class=3D"x_protonmail_signature_block-user">
<div>-Ryan<br>
</div>
</div>
<div class=3D"x_protonmail_signature_block-proton x_protonmail_signature_bl=
ock-empty">
<br>
</div>
</div>
<div><br>
</div>
<div>=1B$B!>!>!>!>!>!>!>=1B(B Original Message =1B$B!>!>!>!>!>!>!>=1B(B<br>
</div>
<div>On Monday, March 18, 2019 3:55 AM, Kenshiro \[\] via bitcoin-dev &lt;b=
itcoin-dev@lists.linuxfoundation.org&gt; wrote:<br>
</div>
<div><br>
</div>
<blockquote class=3D"x_protonmail_quote" type=3D"cite">
<div style=3D"font-family:Calibri,Helvetica,sans-serif; font-size:12pt; col=
or:rgb(0,0,0)">
<div><span>Hi,<br>
</span></div>
<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>
<div><span>Regards,</span><br>
</div>
</div>
</blockquote>
<div><br>
</div>
</div>
</div>
</body>
</html>

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