From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: <decker.christian@gmail.com> Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 19CA7157B; Tue, 1 Oct 2019 14:27:45 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ed1-f43.google.com (mail-ed1-f43.google.com [209.85.208.43]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 41BD98B0; Tue, 1 Oct 2019 14:27:44 +0000 (UTC) Received: by mail-ed1-f43.google.com with SMTP id r9so12104339edl.10; Tue, 01 Oct 2019 07:27:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:in-reply-to:references:date:message-id :mime-version; bh=4bcIOqXq+ghsT6pL6ZqCbizZzP1HfcLNnkhCGqw7pfo=; b=NBtw7TvICRlBa5T7cTFLpc/T29rwkK4TOJ/nTo7aMabYE4/SGo9FumCWZ4tuGb3Uhn yFPckx28nqKQPOYqwGbAfhz1sYqQiwrHvpKE3gpQrZPWFLq5aYaxGKqwLSxAYAhhfWQv J3VK8VGhysRCV2K7eN1mnb+kvnrg4esoP/zjl2Jt3fb3bKXxHuqW7K2+mfYYuhADzzhK j4742dkKq/jjYJPSK74f+axuihz4bPnnnBwUL4szf9En4A7Pf07dL0GnfnFcwLiilf9z 55XomKjT+0RE4W3t8p+/0UMSiTYOgnuLmJIfddFMSHKyJD9EZ2NWyGbcyA7/MQglyE+N wLPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=4bcIOqXq+ghsT6pL6ZqCbizZzP1HfcLNnkhCGqw7pfo=; b=rFLrncC2EpseEbE9e8oJR5UGfgFt6mJcWIWoP1yu3oR+J0kPyzmrJJI+uM6CM0Y6Yo ENMFQLyaS/8HQILziDZ3eFSEyD/6DpN7bdfRkvXlGvEY650SZW7NGzKLAABax7WIw0CR C7qBbu7JfMwr5FKyCWrZwt6pfqhu6U/UMS09z0xO5c11uyoHKHbUZMndev2aAYv1XkXi 4N6HIWPn4aCvlxl4AKiaKsu4ur27ZFTM6so0DIKTBzm8s+xiNvVFmFNyp4gbXtcgXPid biZGSYGBK4VH/weI/aFZUHZdAyANSM/GpNbG/7g0MVvlkD6dgpGwoodZJgdpAjWtMIt/ oquA== X-Gm-Message-State: APjAAAWkyMthx/klPN7vq02cC6FqDJVhLIyJsOUW2ViTkn6gMpN7LgoK Bwup9hd7h3RDnahf2V7ecDJLtHA/t4I= X-Google-Smtp-Source: APXvYqynx5pZc1pdHRTMM9qDylTFdcbETn+SPKjR7KDWtyDk7Tp/IDXfpbFi4h1AO4Eoj5oQyhirJQ== X-Received: by 2002:a17:906:3108:: with SMTP id 8mr24176551ejx.11.1569940062713; Tue, 01 Oct 2019 07:27:42 -0700 (PDT) Received: from localhost ([2a02:aa16:1102:5480:dde:e0b1:d1a1:c9fa]) by smtp.gmail.com with ESMTPSA id k14sm1860366ejp.89.2019.10.01.07.27.41 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 01 Oct 2019 07:27:42 -0700 (PDT) From: Christian Decker <decker.christian@gmail.com> To: ZmnSCPxj <ZmnSCPxj@protonmail.com>, Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org> In-Reply-To: <-5H29F71ID9UFqUGMaegQxPjKZSrF1mvdgfaaYtt_lwI7l1OTmN_8OgcooyoMt2_XuyZ5aDljL6gEup9C7skF8iuP_NbMW_81h0tJIGbJno=@protonmail.com> References: <87wodp7w9f.fsf@gmail.com> <-5H29F71ID9UFqUGMaegQxPjKZSrF1mvdgfaaYtt_lwI7l1OTmN_8OgcooyoMt2_XuyZ5aDljL6gEup9C7skF8iuP_NbMW_81h0tJIGbJno=@protonmail.com> Date: Tue, 01 Oct 2019 16:20:25 +0200 Message-ID: <87tv8s7djq.fsf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, 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 Cc: "lightning-dev@lists.linuxfoundation.org" <lightning-dev@lists.linuxfoundation.org> Subject: Re: [bitcoin-dev] Continuing the discussion about noinput / anyprevout 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: Tue, 01 Oct 2019 14:27:45 -0000 ZmnSCPxj <ZmnSCPxj@protonmail.com> writes: > I rather strongly oppose output tagging. > > The entire point of for example Taproot was to reduce the variability > of how outputs look like, so that unspent Taproot outputs look exactly > like other unspent Taproot outputs regardless of the SCRIPT (or lack > of SCRIPT) used to protect the outputs. That is the reason why we > would prefer to not support P2SH-wrapped Taproot even though > P2SH-wrapping was intended to cover all future uses of SegWit, > including SegWit v1 that Taproot will eventually get. That is a bit reductive if you ask me. Taproot brings a number of improvements such as the reduction of on-chain footprint in the collaborative spend case, the hiding of complex logic in that case, and yes, the uniformity of UTXOs that you mentioned. I do agree that it'd be to make everything look identical to the outside observer, but saying that separating outputs into two coarse-grained domains is equivalent to throwing the baby out with the bath-water :-) That being said, I should clarify that I would prefer not having to make special accomodations on top of the raw sighash_noinput proposal, for some perceived, but abstract danger that someone might shoot themselves in the foot. I think we're all old enough not to need too much handholding :-) Output tagging is my second choice, since it minimizes the need for people to get creative to work around other proposals, and minimizes the on-chain footprint, and finally chaperone signatures are my least preferred option due to its heavy-handed nature and the increased cost. > Indeed, if it is output tagging that gets into Bitcoin base layer, I > would strongly suggest the below for all Decker-Russell-Osuntokun > implementations: > > * A standard MuSig 2-of-2 bip-schnorr SegWit v1 Funding Transaction Output, confirmed onchain > * A "translator transaction" spending the above and paying out to a SegWit v16 output-tagged output, kept offchain. > * Decker-Russell-Osuntokun update transaction, signed with `SIGHASH_NOINPUT` spending the translator transaction output. > * Decker-Russell-Osuntokun state transaction, signed with `SIGHASH_NOINPUT` spending the update transaction output. That is very much how I was planning to implement it anyway, using a trigger transaction to separate timeout start and the actual update/settlement pairs (cfr. eltoo paper Section 4.2). So for eltoo there shouldn't be an issue here :-) > The point regarding use of a commonly-known privkey to work around > chaperone signatures is appropriate to the above, incidentally. In > short: this is a workaround, plain and simple, and one wonders the > point of adding *either* chaperones *or* output tagging if we will, in > practice, just work around them anyway. Exactly, why introduce the extra burden of chaperone signatures or output tagging if we're just going to sidestep it? > Again, the *more* important point is that special blockchain > constructions should only be used in the "bad" unilateral close case. > In the cooperative case, we want to use simple plain > bip-schnorr-signed outputs getting spent to further bip-schnor/Taproot > SegWit v1 addresses, to increase the anonymity set of all uses of > Decker-Russell-Osuntokun and other applications that might use > `SIGHASH_NOINPUT` in some edge case (but which resolve down to simple > bip-schnorr-signed n-of-n cases when the protocol is completed > successfully by all participants). While I do agree that we should keep outputs as unidentifiable as possible, I am starting to question whether that is possible for off-chain payment networks since we are gossiping about the existence of channels and binding them to outpoints to prove their existence anyway. Not the strongest argument I know, but there's little point in talking ideal cases when we need to weaken that later again. >> Open questions >> >> --------------- >> >> The questions that remain to be addressed are the following: >> >> 1. General agreement on the usefulness of noinput / anyprevoutanyscript / >> anyprevout. While at the CoreDev meeting I think everybody agreed that >> these proposals a useful, also beyond eltoo, not everybody could be >> there. I'd therefore like to elicit some feedback from the wider community. > > I strongly agree that `NOINPUT` is useful, and I was not able to attend CoreDev (at least, not with any human fleshbot already known to you --- I checked). Great, good to know that I'm not shouting into the void, and that I'm not just that crazy guy trying to get his hairbrained scheme to work :-) >> 2. Is there strong support or opposition to the chaperone signatures >> introduced in anyprevout / anyprevoutanyscript? I think it'd be best to >> formulate a concrete set of pros and contras, rather than talk about >> abstract dangers or advantages. > > No opposition, we will just work around this by publishing a common > known private key to use for all chaperone signatures, since all the > important security is in the `NOINPUT` signature anyway. > >> >> 3. The same for output tagging / explicit opt-in. What are the advantages and >> disadvantages? > > Strongly oppose, see above about my argument. > >> >> 4. Shall we merge BIP-118 and bip-anyprevout. This would likely reduce the >> confusion and make for simpler discussions in the end. > > Ambivalent, mildly support. > >> >> 5. Anything I forgot to mention :-) > > Cats are very interesting creatures, and are irrelevant to `SIGHASH_NOINPUT` discussion, but are extremely cute nonetheless. Definitely agreed :+1: