From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 2A30D19EA for ; Fri, 22 Mar 2019 16:05:21 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40133.protonmail.ch (mail-40133.protonmail.ch [185.70.40.133]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 3EECB91A for ; Fri, 22 Mar 2019 16:05:20 +0000 (UTC) Date: Fri, 22 Mar 2019 16:05:13 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1553270717; bh=0ETG1HYJ3FaNm4GED54Z7GU+C7XR7mkhXXCWDQevsYE=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References: Feedback-ID:From; b=cU0870ZGrCEwYtYFJJL8DOib37lUbzdhkX4g3x/8rk17t6hy929EZws66ufwK9j4T wkSYd7Lhx7JC9NFYg0etIlknVWNa7HRSEKKcWiH1W/5LYTkdOJkwnNxlYfeUqveG6j nd1QzLMlIX0hIf9Fy0jL9LATmf/rhEnhLkSfUc9Q= To: "Kenshiro \\[\\]" , Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: <8lijztpZXhFjjVzlRV1LGtSulNfgYNiZzRmzpO7epoZRjwswnAtqne9TsEpGOqNxL6NTTH-G4xUrusKRjG-Rl7Y5cAOCtvEXiC5QDbWne7U=@protonmail.com> In-Reply-To: References: Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, FROM_LOCAL_NOVOWEL, RCVD_IN_DNSWL_LOW 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: Fri, 22 Mar 2019 17:09:35 +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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 22 Mar 2019 16:05:21 -0000 Good morning, > >There's certainly some interesting about the idea of "pre-fragmenting" 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 transa= ctions. > > For users that really want privacy it should not be a problem. When a wal= let receive a high amount of btc (+100$ or another amount defined by the us= er) 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 s= plitted again. Small amount addresses + Payjoin could give real privacy to = bitcoin users. Users that don't want privacy could disable the "Private" mo= de in the wallet and disable the auto-splitting feature.=C2=A0 > > i.e.: you receive 1000$ in btc and the wallet make an automatic transacti= on to itself to 10 addresses, 100$ each. > It seems to me, to interact somewhat with ZeroLink. Under ZeroLink, post-mix UTXOs must not be combined. (Basic Post-Mix Wallet Requirement: "Post-mix wallet MUST prevent joining i= nputs together.") The upshot of this, for practical use, is that as payments are done by the = user, available coins become smaller and smaller. And the maximum amount the user can pay with, is limited by the largest pos= t-mix coin they have. If a ZeroLink post-mix wallet were to split its UTXOs as soon as it got the= m from the mix, then it would immediately find itself limiting the maximum = amount the user could pay. I suppose if the ZeroLink post-mix wallet had multiple post-mix coins, it c= ould split one of them for the same purpose as above. Another thought, is if a ZeroLink post-mix wallet could support a Payjoin, = as either receiver or sender. Naively, it seems to me to improve privacy to do so, as long as the ZeroLin= k post-mix wallet only provides a single UTXO to the Payjoin, whether as re= ceiver or sender. For a ZeroLink post-mix wallet to a ZeroLink post-mix wallet Payjoin, this = would typically result in a two-input, two-output transaction, with both pa= rticipants having one input and one output each in the transaction, but dif= ficult (?) for third parties to determine which input/output belongs to whi= ch. Now, if we suppose that both ZeroLink and Payjoin become commonly used, the= n it is likely that two users using the same Chaumian CoinJoin mix transact= ion will find that one needs to pay the other. Thus hopefully it may become common for a Chaumian CoinJoin mix transaction= to have outputs that (directly or indirectly) merge into Payjoin two-input= two-output transactions. This can then be used to allow a ZeroLink post-mix wallet some limited amou= nt of merging its post-mix UTXOs. For instance, if a ZeroLink post-mix wallet has a 0.25BTC and a 0.15BTC coi= n, and needs to pay 0.3 BTC, it may very well simulate a Payjoin to itself,= and create a transaction (0.25, 0.15) -> (0.35, 0.05). Then it can use the 0.35BTC output to pay the 0.3 BTC. Possibly, anyway. Regards, ZmnSCPxj