From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-4.v43.ch3.sourceforge.com ([172.29.43.194] helo=mx.sourceforge.net) by sfs-ml-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1TJ5UC-0005iN-51 for bitcoin-development@lists.sourceforge.net; Tue, 02 Oct 2012 16:38:20 +0000 Received-SPF: pass (sog-mx-4.v43.ch3.sourceforge.com: domain of gmail.com designates 74.125.82.53 as permitted sender) client-ip=74.125.82.53; envelope-from=mh.in.england@gmail.com; helo=mail-wg0-f53.google.com; Received: from mail-wg0-f53.google.com ([74.125.82.53]) by sog-mx-4.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1TJ5UB-0003Bz-05 for bitcoin-development@lists.sourceforge.net; Tue, 02 Oct 2012 16:38:20 +0000 Received: by wgbdr1 with SMTP id dr1so3938773wgb.10 for ; Tue, 02 Oct 2012 09:38:12 -0700 (PDT) MIME-Version: 1.0 Received: by 10.180.86.202 with SMTP id r10mr23112038wiz.12.1349195892790; Tue, 02 Oct 2012 09:38:12 -0700 (PDT) Sender: mh.in.england@gmail.com Received: by 10.216.159.131 with HTTP; Tue, 2 Oct 2012 09:38:12 -0700 (PDT) Date: Tue, 2 Oct 2012 18:38:12 +0200 X-Google-Sender-Auth: ZXyFbB1lHOAYhlhC6MqqyM3cONg Message-ID: From: Mike Hearn To: Bitcoin Dev Content-Type: text/plain; charset=UTF-8 X-Spam-Score: -1.5 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (mh.in.england[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1TJ5UB-0003Bz-05 Subject: [Bitcoin-development] Payment protocol thoughts X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 02 Oct 2012 16:38:20 -0000 I've been thinking about the requirements for a payment protocol lately. It seems we have consensus that we need one of these. Pieter has a gist on the topic here: https://gist.github.com/1237788 IMHO we'll want to move away from "send X BTC to address Y" and more towards "upload to me transactions that send X BTC to outputs A,B....F,G". In this context by output I mean the obvious interpretation of script+value. The reasons are privacy and security. Privacy: you don't want people to find out if you have an unexpectedly large balance (from the block chain). Example worst case scenarios - in a hypothetical Bitcoin-using country, as most people receive income exactly once a month from their employer, you could potentially find out other peoples salaries. Drama ensues. - business partners could find out their counterparty has an unexpectedly good financial position, messing up negotiations Security: - some of the outputs could be in a hot wallet, others in cold wallets, helping you maintain correct balances between them in real time - the outputs can be multi-sig scripts Wallets would then craft a series of transactions to try and somewhat balance the size of inputs vs outputs. Because they are separate transactions and all the keys are fresh, there's no way to link them together into a single payment, especially not if they're broadcast in random order with some jitter. The upside of this is better privacy. The downside is obviously more transactions and therefore more overhead. In theory the sum of tx outputs would end up converging to a reasonable "coin size" for the recipients, eg, businesses might be happy to receive a lot of money in a single output, individuals less, children or very poor people maybe much less. Let's call payment requests invoices. Here is a brainstorm on other features that may be desirable. I'm not suggesting they're all in v1, just that we think about them a bit to ensure we don't paint ourselves into a corner. - Optional list of {signature, certificate} pairs. SSL certs can be embedded into the payment request file itself so they can be checked instantly for wallets that want to show a verified identity, but you can also provide other certificates issued outside the regular SSL CA system. For example maybe MtGox issues you a "trusted vendor" certificate. Maybe the better business bureau issues you a cert, etc. - Optional expiry time (from sipas gist) so outputs that were never sent to can be recycled - Upload target (URI), where to send the created transactions - Optional message and branding image/icon that a wallet can display to make the transaction history a bit prettier - Opaque token that the wallet is supposed to copy into the payment. The merchant can use to link invoice with payment. It's technically redundant, the output set would identify the invoice too, as could a token in the upload target URL, but it may be simpler for some merchant implementations - Ability to specify payment amount[s] in terms of other currencies. If the amount is specified statically it can just be recorded in the wallet for informational purposes. If there's a URL provided also, it is an endpoint where quotes can be obtained. This allows merchants to make long-lived invoices which are protected against FX volatility. Downside: complicates wallets. Upsides: invoices can be kept around for longer. - Web/human-usable URL for the order so users can, eg, send messages to the merchant specific to an order, post a review of the merchant, etc - Support for setting up 2-of-3 dispute mediation. Invoices should be able to name a list of acceptable mediators and the wallet software can intersect this with a list of mediators acceptable to the user, to find one that works best. The whole mechanism by which merchants and users agree on mediators isn't designed yet but we can at least think about it now. It may be there's a simple design everyone agrees on already. - Support for requesting recurring payments. Eg, I should be able to provide N sets of M outputs, one set for each payment with a payment schedule. Wallets can then ensure they run at the appropriate times to keep up the subscription. - Suggested tip/service charge. Wallet would give a simple UI to adjust this up/down by X percentage points - Request to sign inputs with SIGHASH_ANYONECANPAY, allowing the payment to be a pledge for an assurance contract - Ability to specify minimum confirmation level of coins that will be spent. Some merchants may be OK with you immediately re-spending unconfirmed coins. Other merchants will care more and might want you to take on the burden of getting your transactions into the chain. On the payment upload side: - An optional signature under a stable user key that lets users optionally link their payments across merchants. In this way a user can build cross-market reputation which may help them in future, by relaxing confirmation requirements or reducing the chance of being asked to enter dispute mediation. Needs more thought. - Optionally, an invoice for a refund if the merchant chooses to refund the money in the absence of dispute mediation. - A list of Bitcoin transactions that make payments to the outputs requested in the invoice - The opaque token provided in the invoice Re: format. I would (surprise) strongly suggest protocol buffers over JSON. I cannot think of any justification for using JSON (for anything) but especially not for data structures that mostly contain binary data like hashes or keys. Protobufs are easier to work with in code, have a more efficient encoding, can be printed/parsed from ASCII if you need to (eg for debugging purposes) and have fewer sharp edges than JSON does.