Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 400A92371 for ; Wed, 30 Jan 2019 08:34:55 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40135.protonmail.ch (mail-40135.protonmail.ch [185.70.40.135]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 980B75D4 for ; Wed, 30 Jan 2019 08:34:54 +0000 (UTC) Date: Wed, 30 Jan 2019 08:34:46 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1548837292; bh=H+16a8rbk8ix4xEzpI2ARRW1b/0lWni4oVEI3zqMGac=; h=Date:To:From:Reply-To:Subject:In-Reply-To:References:Feedback-ID: From; b=Ak2n2Rmrl29U9Hnwt+3S9CogwqOnQR91uNfJsVGeVW5+5VNWsrpDIYsgmKCqqI3EI PpahLZmHb0IaT10JpuNAUQCB6Qu4TzaFyuTWhhj9tTxxHrcfbPKsXOcXitXWir1Wow RdjYVKpuR5YBpbxKFFlSt7jUZ1lMe+LqKVvpH9ZU= To: Adam Gibson , Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: <226c43d8-1fad-9d90-ba47-9230118e447d@gmail.com> References: <-yZhdFkKfKAEz1_4GKKSpTxjvR8EDSsH_5-TTh_4X5qwa79igXKR14rh6JASrald-F97o1htWY_kcBQ7IVr7ZH9zOQlOEwzhkWDjTq0d7F4=@protonmail.com> <-NShvd5jVPHb7_QmmjQMHX4f-O53noLWK8DKl37mJGcNlIvGoGbBrJVAwly9cHtLrB1tSz8FVL_wSMvaj2uAA760Sgr4Mg6M4VQuKZx0m7w=@protonmail.com> <226c43d8-1fad-9d90-ba47-9230118e447d@gmail.com> 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: Wed, 30 Jan 2019 08:57:48 +0000 Subject: Re: [bitcoin-dev] bustapay BIP :: a practical sender/receiver coinjoin protocol 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: Wed, 30 Jan 2019 08:34:55 -0000 Good morning Adam, > And I'm reminded that a related point is made by belcher in the gist > comment thread iirc (after we discussed it on IRC): over time a > "PayJoin-only" merchant doing the simplest thing - using a single utxo > over and over again, will concentrate more and more funds into it, and > inevitably violating UIH2 in an increasingly dramatic fashion > (contributing a 100BTC utxo to a 0.1BTC payment etc.). Suggesting it's > better if there's a mix of payjoin/non-payjoin. To be pedantic: as I understand bustapay, it would still not violate UIH2 (= unless I misunderstand UIH2). Suppose the original transaction is: (0.05 payer, 0.07 payer) -> (0.1 payee= , 0.02 payer) Then bustapay with such a PayJoin-only merchant with 100BTC UTXO would give= : (100 payee, 0.05 payer, 0.07 payer) -> (100.1 payee, 0.02 payer). As I understand it, this technically does not violate UIH2. It would still conceivably be interpreted as a payment of 100.1 BTC, from a= payer who happens to have massively lopsided UTXOs being owned, but still = does not violate UIH2. However, if that 100.1 UTXO is subsequently used to pay a 100.3 payment, th= en that is used to pay a 100.7 payment, that strongly suggests such a naive= PayJoin-only merchant. Perhaps a simple heuristic against this would be: 1. For every UTXO you own, flip a coin. If all of them come up heads, do not payjoin; just broadcast the origin= al transaction. 2. Else, randomly select a UTXO (value not care?) and payjoin with that UT= XO. However, I have no proper analysis of the blockchain, so -- Regards, ZmnSCPxj