From: Damian Williamson <willtech@live.com.au>
To: "bitcoin-dev@lists.linuxfoundation.org"
	<bitcoin-dev@lists.linuxfoundation.org>
Thread-Topic: feature: Enhance privacy by change obfuscation
Thread-Index: AQHTvlhNAdeVyrmKfEykHDGYNxE3lg==
Date: Sun, 18 Mar 2018 01:34:20 +0000
Message-ID: <PS2P216MB0179FCA8077AAE946BFA2D069DD50@PS2P216MB0179.KORP216.PROD.OUTLOOK.COM>
Accept-Language: en-AU, en-US
Content-Language: en-AU
x-ms-exchange-messagesentrepresentingtype: 1
x-tmn: [6Le4IxGD/iX2mh37463V+vl2P34ll1Is]
x-ms-publictraffictype: Email
x-microsoft-exchange-diagnostics: 1; PU1APC01HT133;
	6:5quRDahvHXin26E2PAHRf8WRYnoBt68QJqD4ZDOjOCTsBKQmWad2BnVb7Z4b9FmbX/dsWJng9mlBxxlMlsC24Nix8qVQ29HjM2JG0aFejjsOgCM9aMj/XQkYbqvBpyjnkpYYnu2pW4gQ6TN7vWAHiF8w+eGS+vmP5OXYU8MkOz8S/FTHOvz8/HUHof17xmbOqVmMrFhGHxrRPnPoN+f/bHeWKtGv2yPiTszLSetopFPDTjagSwtxeXxL6uFY1V0PToEQBnocb6IYR8u8jqTgLsMUSmRrF211umAMaoSX4+AQf9S5N62eO6rmHYEP82LstncU/sRyIbGUh/Hoe5aCNkADIeVH1tdrWQu84xgfUs4=;
	5:8zWa3KSEfyqZwOErIbciIyxAy9zmLpDVcltC17zSqI9pdmV17ytmqqV3+zWDBFN+HwszM8MtpxyZtAltzc3H6WR89LyxNvke5sHrBNij7/nzEWbTyR+MbLVlQ1JUzr1G3THc57mME+AHdLasvkWx1qb0Kkm7xSPnvcZdoYXbyzI=;
	24:yCoP/BkDxYz/cRmAw4r1icediu1u5QR7dJpNxYVj8/o1WTYIt5MSQtrowE95MmRJAJFh5kfuggwirwKRnau+YSgQpVfhLMEt75yN22IwxAg=;
	7:DlB0r4pcBjI75CZ1eyEX6TbzavuuUrQRnRRpakLm2N7nYqaiVJHeGxvK92naWAcJISB5Br5yEL4ZHW99aSyGjhSq9CN81Prm64tUCAY7tf0loGA2OY8TrNwwsiLvmtEZnqSbYhBCLy9CLnVW5aAWibzstEjo2mxMaAeDk8f0UokrSGInb1qNGLIsT98vlxQmvKeles7h/3Ib4a45x+EpLf/OdqLAX9KoeZu4itFdLfU9rCTYCNPLG+wtMDQ/2g26
x-incomingheadercount: 44
x-eopattributedmessage: 0
x-microsoft-antispam: UriScan:; BCL:0; PCL:0;
	RULEID:(7020095)(201702061078)(5061506573)(5061507331)(1603103135)(2017031320274)(2017031324274)(2017031323274)(2017031322404)(1601125374)(1603101448)(1701031045);
	SRVR:PU1APC01HT133; 
x-ms-traffictypediagnostic: PU1APC01HT133:
x-ms-office365-filtering-correlation-id: ac8eae55-94cf-4d6b-4b9d-08d58c705f6d
x-exchange-antispam-report-cfa-test: BCL:0; PCL:0; RULEID:(444000031);
	SRVR:PU1APC01HT133; BCL:0; PCL:0; RULEID:; SRVR:PU1APC01HT133; 
x-forefront-prvs: 06157D541C
x-forefront-antispam-report: SFV:NSPM; SFS:(7070007)(98901004); DIR:OUT;
	SFP:1901; SCL:1; SRVR:PU1APC01HT133;
	H:PS2P216MB0179.KORP216.PROD.OUTLOOK.COM; FPR:; SPF:None; LANG:;
x-microsoft-antispam-message-info: VobkqUGJFSBDCT4NDehL5B4vW79hnYCcym5PWWIOXnmYQsY2V1RDc9HQTOZ5nKsqNZesKlwFv5vHki6/1VXgOVw99RXNfhwIe/TYxNo4GKm9Fc5wVCIdl00FLqWJeyruzDlIIQhS8R21UWKuVRRcrKMdJECv+2mCr88gphyvFu6gBrWGQ3XBSJ3jFEt2PerZ
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: multipart/alternative;
	boundary="_000_PS2P216MB0179FCA8077AAE946BFA2D069DD50PS2P216MB0179KORP_"
MIME-Version: 1.0
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: ac8eae55-94cf-4d6b-4b9d-08d58c705f6d
X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Mar 2018 01:34:20.7236 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Internet
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PU1APC01HT133
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID, HTML_MESSAGE, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1
X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on
	smtp1.linux-foundation.org
X-Mailman-Approved-At: Sun, 18 Mar 2018 01:43:18 +0000
Subject: [bitcoin-dev] feature: Enhance privacy by change obfuscation
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: Sun, 18 Mar 2018 01:34:24 -0000

--_000_PS2P216MB0179FCA8077AAE946BFA2D069DD50PS2P216MB0179KORP_
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

Application: Bitcoin Core

Feature: Enhanced privacy by change obfuscation

Operation: Provide a user selectable 'Enhanced privacy' option for transact=
ion creation, when true the transaction randomly distributes change across =
up to twenty output addresses (minimum five?), provided each output is not =
dust.

Suggestions: Perhaps limit the total random number of addresses to distribu=
te to by change amount. Optionally: If necessary, additional inputs can be =
selected if available to increase change although consider if this may even=
tually result in a decrease in obfuscation in some cases when the outputs a=
re spent.

Issues: Transaction cost will be higher for the initial spend with the chan=
ge due to increased outputs and, possibly for later spending the change dep=
ending on the future spend amount(s) and the number of inputs required.

Argument: If transaction linkage is possible, it is still possible with the=
 obfuscated change but, it is far more difficult to guess what was retained=
 by the owner of the originating utxo's unless the new change outputs are s=
pent together in the same transaction.


Regards,

Damian Williamson

--_000_PS2P216MB0179FCA8077AAE946BFA2D069DD50PS2P216MB0179KORP_
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<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;margi=
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"></p>
<div>Application: Bitcoin Core<br>
<br>
Feature: Enhanced privacy<span>&nbsp;by change obfuscation</span><br>
<br>
Operation: Provide a user selectable 'Enhanced privacy' option for transact=
ion creation, when true the transaction randomly distributes change across =
up to twenty output addresses (minimum five?), provided each output is not =
dust.<br>
<br>
Suggestions: Perhaps limit the total random number of addresses to distribu=
te to by change amount.
<span>Optionally: If necessary, additional inputs can be selected if availa=
ble to increase change although consider if this may eventually result in a=
 decrease in obfuscation in some cases when the outputs are spent.</span><b=
r>
<br>
Issues: Transaction cost will be higher for the initial spend with the chan=
ge due to increased outputs and, possibly for later spending the change dep=
ending on the future spend amount(s) and the number of inputs required.<br>
<br>
Argument: If transaction linkage is possible, it is still possible with the=
 obfuscated change but, it is far more difficult to guess what was retained=
 by the owner of the originating utxo's unless the new change outputs are s=
pent together in the same transaction.<br>
</div>
<p></p>
<p style=3D"margin-top:0;margin-bottom:0"><br>
</p>
<p style=3D"margin-top:0;margin-bottom:0">Regards,</p>
<p style=3D"margin-top:0;margin-bottom:0">Damian Williamson<br>
</p>
</div>
</body>
</html>

--_000_PS2P216MB0179FCA8077AAE946BFA2D069DD50PS2P216MB0179KORP_--