Return-Path: Received: from smtp3.osuosl.org (smtp3.osuosl.org [IPv6:2605:bc80:3010::136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 95557C0012; Wed, 8 Dec 2021 17:41:50 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id 7CF6F607FE; Wed, 8 Dec 2021 17:41:50 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org X-Spam-Flag: NO X-Spam-Score: -4.199 X-Spam-Level: X-Spam-Status: No, score=-4.199 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id SO5kHufgKHmv; Wed, 8 Dec 2021 17:41:49 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) by smtp3.osuosl.org (Postfix) with ESMTPS id 98412607B4; Wed, 8 Dec 2021 17:41:49 +0000 (UTC) Received: from mail-lf1-f52.google.com (mail-lf1-f52.google.com [209.85.167.52]) (authenticated bits=0) (User authenticated as jlrubin@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 1B8HfkAZ006824 (version=TLSv1/SSLv3 cipher=AES128-GCM-SHA256 bits=128 verify=NOT); Wed, 8 Dec 2021 12:41:47 -0500 Received: by mail-lf1-f52.google.com with SMTP id t26so7019083lfk.9; Wed, 08 Dec 2021 09:41:47 -0800 (PST) X-Gm-Message-State: AOAM530idVY7PtRyKY4wkcSB5ZvnwDgrwsOtUsyLVn1gdyQ6BgicTqeG NYW15+owjcjKaFbuwSNlnpqDrdBWU3GdsYJSwAM= X-Google-Smtp-Source: ABdhPJzhq8GNu1Y1GX3f4EduOHr94nxcgGgqDugqLuhKKN1PfaDcNL1QTMS4WISyAzdT5RLlC7X9KS/mEUPtbKjb7GU= X-Received: by 2002:a05:6512:1287:: with SMTP id u7mr870907lfs.226.1638985306278; Wed, 08 Dec 2021 09:41:46 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Jeremy Date: Wed, 8 Dec 2021 09:41:34 -0800 X-Gmail-Original-Message-ID: Message-ID: To: Ruben Somsen Content-Type: multipart/alternative; boundary="000000000000f90f7e05d2a600d4" Cc: Bitcoin Protocol Discussion , lightning-dev Subject: Re: [bitcoin-dev] [Lightning-dev] Take 2: Removing the Dust Limit 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: Wed, 08 Dec 2021 17:41:50 -0000 --000000000000f90f7e05d2a600d4 Content-Type: text/plain; charset="UTF-8" IMO this is not a big problem. The problem is not if a 0 value ever enters the mempool, it's if it is never spent. And even if C2/P1 goes in, C1 still can be spent. In fact, it increases it's feerate with P1's confirmation so it's somewhat likely it would go in. C2 further has to be pretty expensive compared to C1 in order to be mined when C2 would not be, so the user trying to do this has to pay for it. If we're worried it might never be spent again since no incentive, it's rational for miners *and users who care about bloat* to save to disk the transaction spending it to resurrect it. The way this can be broken is if the txn has two inputs and that input gets spent separately. That said, I think if we can say that taking advantage of keeping the 0 value output will cost you more than if you just made it above dust threshold, it shouldn't be economically rational to not just do a dust threshold value output instead. So I'm not sure the extent to which we should bend backwards to make 0 value outputs impossible v.s. making them inconvenient enough to not be popular. ------------------------------------- Consensus changes below: ------------------------------------- Another possibility is to have a utxo with drop semantics; if UTXO X with some flag on it is not spent in the block it is created, it expires and can never be spent. This is essentially an inverse timelock, but severely limited to one block and mempool evictions can be handled as if a conflict were mined. These types of 0 value outputs could be present just for attaching fee in the mempool but be treated like an op_return otherwise. We could add two cases for this: one bare segwit version (just the number, no data) and one that's equivalent to taproot. This covers OP_TRUE anchors very efficiently and ones that require a signature as well. This is relatively similar to how Transaction Sponsors works, but without full tx graph de-linkage... obviously I think if we'll entertain a consensus change, sponsors makes more sense, but expiring utxos doesn't change as many properties of the tx-graph validation so might be simpler. --000000000000f90f7e05d2a600d4 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
IMO this is not a big = problem. The problem is not if a 0 value ever enters the mempool, it's = if it is never spent. And even if C2/P1 goes in, C1 still can be spent. In = fact, it increases it's feerate with P1's confirmation so it's = somewhat likely it would go in. C2 further has to be pretty expensive compa= red to C1 in order to be mined when C2 would not be, so the user trying to = do this has to pay for it.

If we're worried it might never = be spent again since no incentive, it's rational for miners *and users = who care about bloat* to save to disk the transaction spending it to resurr= ect it. The way this can be broken is if the txn has two inputs and that in= put gets spent separately.

That said, I think if we can say tha= t taking advantage of keeping the 0 value output will cost you more than if= you just made it above dust threshold, it shouldn't be economically ra= tional to not just do a dust threshold value output instead.

So= I'm not sure the extent to which we should bend backwards to make 0 va= lue outputs impossible v.s. making them inconvenient enough to not be popul= ar.



-------------------------------------
Consensus changes below:
-------------------------------------

Another possibility is to have a utxo with drop semantics; if UTXO X wit= h some flag on it is not spent in the block it is created, it expires and c= an never be spent. This is essentially an inverse timelock, but severely li= mited to one block and mempool evictions can be handled as if a conflict we= re mined.

These types of 0 value outputs could be present just = for attaching fee in the mempool but be treated like an op_return otherwise= . We could add two cases for this: one bare segwit version (just the number= , no data) and one that's equivalent to taproot. This covers OP_TRUE an= chors very efficiently and ones that require a signature as well.

This is relatively similar to how Transaction Sponsors works, but withou= t full tx graph de-linkage... obviously I think if we'll entertain a co= nsensus change, sponsors makes more sense, but expiring utxos doesn't c= hange as many properties of the tx-graph validation so might be simpler.




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