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
Thread-Index: AQHU3Xi3TuLQzioN20KrtFTwOE2knaYWUg2AgAEejBiAABTNWQ==
Date: Fri, 22 Mar 2019 11:15:26 +0000
Message-ID: <DB6PR10MB1832FFFFD06F26525522E826A6430@DB6PR10MB1832.EURPRD10.PROD.OUTLOOK.COM>
References: <DB6PR10MB1832253A8D022C4A91573D49A6470@DB6PR10MB1832.EURPRD10.PROD.OUTLOOK.COM>,
	<LUvvLGfixy2VQURUSkwxavfcxnQeLsUGvjm3o9iKW6EPOj0HIEeIlyhTUVIvaTcL_9NAY8k7CizkoKvSrQMq8b9fjDwxSzFvuAisboJ5jkQ=@protonmail.com>,
	<DB6PR10MB1832829D9C812F50C66BD11CA6430@DB6PR10MB1832.EURPRD10.PROD.OUTLOOK.COM>
In-Reply-To: <DB6PR10MB1832829D9C812F50C66BD11CA6430@DB6PR10MB1832.EURPRD10.PROD.OUTLOOK.COM>
Accept-Language: en-US, es-ES
Content-Language: en-US
Content-Type: multipart/alternative;
	boundary="_000_DB6PR10MB1832FFFFD06F26525522E826A6430DB6PR10MB1832EURP_"
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-Network-Message-Id: f61813a1-d7be-4758-6b87-08d6aeb7af81
X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Mar 2019 11:15:26.5666 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Internet
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1EUR02HT221
X-Spam-Status: No, score=-1.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,FREEMAIL_REPLY,HTML_MESSAGE,
	RCVD_IN_DNSWL_NONE autolearn=no version=3.3.1
X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on
	smtp1.linux-foundation.org
X-Mailman-Approved-At: Fri, 22 Mar 2019 13:41:33 +0000
Subject: Re: [bitcoin-dev] Payjoin privacy with the receiver of the
 transaction
X-BeenThere: bitcoin-dev@lists.linuxfoundation.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Bitcoin Protocol Discussion <bitcoin-dev.lists.linuxfoundation.org>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/bitcoin-dev>,
	<mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/bitcoin-dev/>
List-Post: <mailto:bitcoin-dev@lists.linuxfoundation.org>
List-Help: <mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>,
	<mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=subscribe>
X-List-Received-Date: Fri, 22 Mar 2019 11:15:31 -0000

--_000_DB6PR10MB1832FFFFD06F26525522E826A6430DB6PR10MB1832EURP_
Content-Type: text/plain; charset="iso-2022-jp"
Content-Transfer-Encoding: quoted-printable

They Payjoin protocol could include the possibility of receive "safe" amoun=
ts (i.e.: 0.025 btc) to several addresses so every user using Payjoin alrea=
dy have a splitted balance. Only people receiving a regular public transact=
ion should need the extra splitting transaction.

Regards

________________________________
From: Kenshiro []
Sent: Friday, March 22, 2019 11:23
To: Bitcoin Protocol Discussion; rhavar@protonmail.com
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 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_DB6PR10MB1832FFFFD06F26525522E826A6430DB6PR10MB1832EURP_
Content-Type: text/html; charset="iso-2022-jp"
Content-Transfer-Encoding: quoted-printable

<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);">
They Payjoin protocol could include the possibility of receive &quot;safe&q=
uot; amounts (i.e.:&nbsp;0.025 btc) to several addresses so every user usin=
g Payjoin already have a splitted balance. Only people receiving a regular =
public transaction should need the extra splitting
 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);">
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> Kenshiro []<br>
<b>Sent:</b> Friday, March 22, 2019 11:23<br>
<b>To:</b> Bitcoin Protocol Discussion; rhavar@protonmail.com<br>
<b>Subject:</b> Re: [bitcoin-dev] Payjoin privacy with the receiver of the =
transaction</font>
<div>&nbsp;</div>
</div>
<div dir=3D"ltr">
<div style=3D"font-family:Calibri,Helvetica,sans-serif; font-size:12pt; col=
or:rgb(0,0,0)">
<span style=3D"color:rgb(51,51,51); background-color:rgb(255,255,255); disp=
lay:inline!important">&gt;I'm not really sure the problem you're describing=
, but it sounds like something that affects normal bitcoin transactions as =
well.</span><br>
</div>
<div style=3D"font-family:Calibri,Helvetica,sans-serif; font-size:12pt; col=
or:rgb(0,0,0)">
<span style=3D"color:rgb(51,51,51); background-color:rgb(255,255,255); disp=
lay:inline!important"><br>
</span></div>
<div style=3D"font-size:12pt">Yeah, it affects normal transactions too. But=
 I'm focused in Payjoin because it should allow private transactions. The p=
roblem I see is that Payjoin shouldn't allow that the sender or the receive=
r 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"background-color:rgb(255,255,2=
55); display:inline!important">&gt;There's certainly some interesting about=
 the idea of &quot;pre-fragmenting&quot; 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 users, as=
 it'll generally result in pretty big and cost-ineffective transactions.</s=
pan><br>
</div>
<div style=3D"font-size:12pt"><span style=3D"background-color:rgb(255,255,2=
55); display:inline!important"><br>
</span></div>
<div style=3D"font-size:12pt">For users that really want privacy it should =
not be a problem. When a wallet receive a high amount of btc (&#43;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 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 wallet=
 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 privac=
y than the opposite.</div>
<div style=3D"font-size:12pt"><br>
</div>
<div style=3D"font-size:12pt">Regards</div>
<div>
<div id=3D"x_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"x_divRplyFwdMsg" dir=3D"ltr"><font face=3D"Calibri, sans-serif" =
color=3D"#000000" style=3D"font-size:11pt"><b>From:</b> rhavar@protonmail.c=
om &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_x_protonmail_signature_block">
<div class=3D"x_x_protonmail_signature_block-user">
<div>-Ryan<br>
</div>
</div>
<div class=3D"x_x_protonmail_signature_block-proton x_x_protonmail_signatur=
e_block-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_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>
</div>
</div>
</body>
</html>

--_000_DB6PR10MB1832FFFFD06F26525522E826A6430DB6PR10MB1832EURP_--