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Thu, 20 Aug 2020 15:37:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=riseup.net; s=squak; t=1597963058; bh=CQn60KWBktj/pVgb7XhJQxmVHGjfQjA/0orOXD5j2X8=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=VVX8OQ52GVWWmSa88c7hOd78o3sC1mFgh3GDCbpVXOOSixuKgcXwm0RH5H27VpEjM 0QZXyT0rdT6hLBQwL8PY8FW2MBbqlS2OaxPI9GdyObYMKP9gc5NdCEHXsmLrbzERPk 3ywM72XdZFDoTu156zG9mOUdHfaBBPcrOOO///CQ= X-Riseup-User-ID: 2C5906B5EE1BE43464637A30D0BE79FAA63D2F091D1ED82A6391E3B5122C814C Received: from [127.0.0.1] (localhost [127.0.0.1]) by bell.riseup.net (Postfix) with ESMTPSA id 4BXffn0M0KzJnm7; Thu, 20 Aug 2020 15:37:36 -0700 (PDT) To: ZmnSCPxj , Nadav Kohen References: <813e51a1-4252-08c0-d42d-5cef32f684bc@riseup.net> From: Chris Belcher Autocrypt: addr=belcher@riseup.net; prefer-encrypt=mutual; keydata= xsFNBFPk74oBEACzBLjd+Z5z7eimqPuObFTaJCTXP7fgZjgVwt+q94VQ2wM0ctk/Ft9w2A92 f14T7PiHaVDjHxrcW+6sw2VI2f60T8Tjf+b4701hIybluWL8DntG9BW19bZLmjAj7zkgektl YNDUrlYcQq2OEHm/MGk6Ajt2RA56aRKqoz22e+4ZA89gDgamxUAadul7AETSsgqOEUDI0FKR FODzoH65w1ien/DLkG1f76jd0XA6AxrESJVO0JzvkTnJGElBcA37rYaMmDi4DhG2MY4u63VE 8h6DyUXcRhmTZIAj+r+Ht+KMDiuiyQcKywCzzF/7Ui7YxqeAgjm5aPDU2E8X9Qd7cqHQzFM7 ZCqc9P6ENAk5a0JjHw0d0knApboSvkIJUB0j1xDIS0HaRlfHM4TPdOoDgnaXb7BvDfE+0zSz WkvAns9oJV6uWdnz5kllVCjgB/FXO4plyFCHhXikXjm1XuQyL8xV88OqgDFXwVhKrDL9Pknu sTchYm3BS2b5Xq1HQqToT3I2gRGTtDzZVZV0izCefJaDp1mf49k2cokDEfw9MroEj4A0Wfht 0J64pzlBYn/9zor5cZp/EAblLRDK6HKhSZArIiDR1RC7a6s7oTzmfn0suhKDdTzkbTAnDsPi Dokl58xoxz+JdYKjzVh98lpcvMPlbZ+LwIsgbdH4KZj7mVOsJwARAQABzR9DaHJpcyBCZWxj aGVyIDxmYWxzZUBlbWFpbC5jb20+wsF+BBMBAgAoBQJT5O+KAhsDBQkSzAMABgsJCAcDAgYV CAIJCgsEFgIDAQIeAQIXgAAKCRDvc06md/MRKS8jD/9P9fSYSIVjltL9brAMfIu7wJn0H0lX TbcuCM2uQitJ3BNxI3c7aq5dEby27u5Ud54otncDJuRPQVDKs6H7t1rInitgJ1MTQ9/aQGFA btKcgtVIMFbeClzTTfWr4W7fE45NI7E9EANgk5JfmWh3U+KINYLF5RtqynYocrsP6zOV+G9A HCpBemd9TN60CoMLMyMzTHEW1oQffaVAXY8DgthEYO/odWYIod7VTmEm0zU1aSysPqMwPWNm 8XIl0f8SfKQyZlAU8e1eCFVCenkE44FKC5qQNYc2UxexEYtfCWChTGc4oHKxIyYmTCCefsQF LvgwtvlNHRXHSDKSPSNcRcpl8DFpNEKrmMlkJ8Mx+YR05CydlTQ0bI3FBohJC+UHrjD5I3hA wJUC1o+yVSOEd+zN3cG1EECIwkEQSmBgG5t/le2RdzfXOdpf9ku2/zoBpq00R54JxUKlfRM7 OPTv7X+1AKHkxOySdCZwGgvdh2Whuqs4kTvtco00gCFM9fBd5oi1RJuHtxHsj8+/XU15UItb jeo96CIlM5YUeoRLPT5mxZYWgYAARFeSFReNq/Tuwq9d8EokUrtAyrPayznliy53UJfWDVzl 925c0Cz0HWaP2fWj+uFcj/8K0bhptuWJQy0Poht1z3aJC1UjEgr1Xz8I7jeSJmIlA9plcJw2 k4dhWc7BTQRT5O+KARAAyFxAM28EQwLctr0CrQhYWZfMKzAhCw+EyrUJ+/e4uiAQ4OyXifRr ZV6kLRul3WbTB1kpA6wgCShO0N3vw8fFG2Cs6QphVagEH8yfQUroaVxgADYOTLHMOb7INS8r KI/uRNmE6bXTX27oaqCEXLMycqYlufad7hr42S/T8zNh5m2vl6T/1Poj2/ormViKwAxM+8qf xd8FNI4UKmq2zZE9mZ5PiSIX0qRgM0yCvxV39ex/nhxzouTBvv4Lb1ntplR/bMLrHxsCzhyM KDgcX7ApGm+y6YEsOvzw9rRCRuJpE4lth8ShgjTtNTHfklBD6Ztymc7q7bdPWpKOEvO5lDQ6 q8+KfENv862cOLlWLk7YR2+mHZ1PXGhWC7ggwEkfGJoXo0x8X+zgUKe2+9Jj4yEhfL0IbFYC z2J5d+cWVIBktI3xqkwLUZWuAbE3vgYA4h8ztR6l18NTPkiAvpNQEaL4ZRnAx22WdsQ8GlEW dyKZBWbLUdNcMmPfGi5FCw2nNvCyN6ktv5mTZE12EqgvpzYcuUGQPIMV9KTlSPum3NLDq8QI 6grbG8iNNpEBxmCQOKz2/BuYApU2hwt2E44fL8e6CRK3ridcRdqpueg75my6KkOqm8nSiMEc /pVIHwdJ9/quiuRaeC/tZWlYPIwDWgb8ZE/g66z35WAguMQ+EwfvgAUAEQEAAcLBZQQYAQIA DwUCU+TvigIbDAUJEswDAAAKCRDvc06md/MRKaZwD/9OI3o3gVmst/mGx6hVQry++ht8dFWN IiASPBvD3E5EWbqWi6mmqSIOS6CxjU0PncxTBPCXtzxo/WzuHGQg/xtNeQ0T8b2lBScZAw93 qm1IcHXLUe5w/Tap6YaDmSYCIZAdtbHzYfPW4JK7cmvcjvF8jhTFOBEOFVQkTi19G7caVot0 +wL1e2DRHDXAe5CinEpaLBlwHeEu/5j6wc3erohUZlK9IbAclj4iZTQbaq3EyqUXl59dBOON xmL5edJxzVishIYQGIyA9WP1SylXt+kO82NEqZG2OxdXAlzjuJ8C2pAG+nbLtDo4hcsiN/MA aX9/JB7MXclT5ioerF4yNgKEdfq7LmynsTUd8w/Ilyp7AD+BWoujyO94i8h9eKvjf9PvSwxQ uAjRpxne7ZJD8vCsMNXBHSbeEK2LiwStHL/w473viXpDD53J6OLxX6a5RummR+rixbMH7dgK MJQ7FlyDphm3or6CSkGEir1KA0y1vqQNFtHhguFapAWMDKaJjQQNgvZUmOo6hbZqmvUF1OWc d6GA6j3WOUe3fDJXfbq6P9Jmxq64op887dYKsg7xjQq/7KM7wyRcqXXcbBdgvNtVDP+EnzBN HyYY/3ms4YIHE5JHxQ9LV4yPcWkYTvb1XpNIFVbrSXAeyGHVNT+SO6olFovbWIC3Az9yesaM 1aSoTg== Message-ID: Date: Thu, 20 Aug 2020 23:37:35 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Detailed protocol design for routed multi-transaction CoinSwap X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Aug 2020 22:37:39 -0000 Hello Nadav and ZmnSCPxj, On 20/08/2020 22:38, ZmnSCPxj wrote: > Good morning Nadav, > >> Hey Chris and all, >> >> Looking good :) I have one major concern though >> >>>     q = EC privkey generated by maker >>>     Q = q.G = EC pubkey published by maker >>> >>>     p = nonce generated by taker >>>     P = p.G = nonce point calculated by taker >>> >>>     R = Q + P = pubkey used in bitcoin transaction >>>       = (q + p).G >> >> If I'm understanding this correctly (which I'm not sure I ame), it seems like the plan is to put R on-chain as the key to an output? As stated this is completely insecure as Q is known in advance so the taker can always choose a nonce p but then claim that their nonce point is p.G - Q so that the key that goes on-chain is (p.G - Q + Q) = p.G allowing them to steal the funds. > > My reading from this is that nonce `p` has to be given by the taker to the maker outright. > In original post: > >> Taker sends unsigned transaction which pays to multisig using pubkey Q, >> and also sends nonce p. > > Thus, taker provides a proof-of-knowledge, i.e. the actual `p` scalar itself (not zero-knowledge, but what the maker needs is proof-of-knowledge, and could not care less if the proof is zero-knowledge or not). Yes this looks right. In hindsight my text could be clarified by changing the relevant lines to: p = nonce generated by taker, sent to maker P = p.G = nonce point calculated by taker R = Q + P = pubkey used in bitcoin transaction, calculated by taker = (q + p).G = same pubkey, calculated by maker I don't think the key subtraction attack described by Nadav will work here...? > On the other hand, I do not see the point of this tweak if you are going to use 2p-ECDSA, since my knowledge is that 2p-ECDSA uses the pubkey that is homomorphic to the product of the private keys. > And that pubkey is already tweaked, by the fresh privkey of the maker (and the maker is buying privacy and wants security of the swap, so is incentivized to generate high-entropy temporary privkeys for the actual swap operation). > > Not using 2p-ECDSA of some kind would remove most of the privacy advantages of CoinSwap. > You cannot hide among `2 2 OP_CHECKMULTISIG` scripts of Lightning, because: > > * Lightning channel closes tend to be weeks at least after the funding outpoint creation, whereas CoinSwap envisions hours or days. > * Lightning mutual channel closes have a very high probability of spending to two P2WPKH addresses. > > You need to hide among the much larger singlesig anonymity set, which means using a single signature (created multiparty by both participants), not two signatures (one from each participant). > > Or is this intended for HTLCs in open-coded SCRIPTs `OP_DUP OP_IF OP_HASH160 OP_EQUAL OP_ELSE