From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 366DBC0733 for ; Tue, 14 Jul 2020 09:37:46 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id DB71D23449 for ; Tue, 14 Jul 2020 09:37:44 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TnHtlOUTKG5D for ; Tue, 14 Jul 2020 09:37:43 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from azure.erisian.com.au (cerulean.erisian.com.au [139.162.42.226]) by silver.osuosl.org (Postfix) with ESMTPS id 9BA92204EF for ; Tue, 14 Jul 2020 09:37:42 +0000 (UTC) Received: from aj@azure.erisian.com.au (helo=sapphire.erisian.com.au) by azure.erisian.com.au with esmtpsa (Exim 4.89 #1 (Debian)) id 1jvHNZ-0000wl-1z for ; Tue, 14 Jul 2020 19:37:39 +1000 Received: by sapphire.erisian.com.au (sSMTP sendmail emulation); Tue, 14 Jul 2020 19:37:30 +1000 Date: Tue, 14 Jul 2020 19:37:30 +1000 From: Anthony Towns To: Bitcoin Protocol Discussion Message-ID: <20200714093730.myvls2jfpwyi3ap3@erisian.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: NeoMutt/20170113 (1.7.2) X-Spam-Score-int: -18 X-Spam-Bar: - Subject: [bitcoin-dev] Thoughts on soft-fork activation 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: Tue, 14 Jul 2020 09:37:46 -0000 Hi, I've been trying to figure out a good way to activate soft forks in future. I'd like to post some thoughts on that. So: I think there's two proposals that are roughly plausible. The first is Luke's recent update to BIP 8: https://github.com/bitcoin/bips/blob/master/bip-0008.mediawiki It has the advantage of being about as simple as possible, and (in my opinion) is an incremental improvement on how segwit was activated. Its main properties are: - signalling via a version bit - state tansitions based on height rather than median time - 1 year time frame - optional mandatory activation at the end of the year - mandatory signalling if mandatory activation occurs - if the soft fork activates on the most work chain, nodes don't risk falling out of consensus depending on whether they've opted in to mandatory activation or not I think there's some fixable problems with that proposal as it stands (mostly already mentioned in the comments in the recently merged PR, https://github.com/bitcoin/bips/pull/550 ) The approach I've been working on is based on the more complicated and slower method described by Matt on this list back in January. I've got a BIP drafted at: https://github.com/ajtowns/bips/blob/202007-activation-dec-thresh/bip-decthresh.mediawiki The main difference with the mechanism described in January is that the threshold gradually decreases during the secondary period -- it starts at 95%, gradually decreases until 50%, then mandatorily activates. The idea here is to provide at least some potential reward for miners signalling in the secondary phase: if 8% of hashpower had refused to signal for a soft-fork, then there would have been no chance of activating until the very end of the period. This way, every additional percentage of hashpower signalling brings the activation deadline forward. The main differences between the two proposals is that the BIP 8 approach has a relatively short time frame for users to upgrade if we want mandatory activation without a supermajority of hashpower enforcing the rules; while the "decreasing threshold" approach linked above provides quite a long timeline. In addition, there is always the potential to introduce a BIP 91/148 style soft-fork after the fact where either miners or users coordinate to have mandatory signalling which then activates a pre-existing deployment attempt. I think the design constraints we want are: * if everyone cooperates and no one objects, we activate pretty quickly * there's no obvious exploits, and we have plausible contingency plans in place to discourage people from try to use the attempt to deploy a new soft fork as a way of attacking bitcoin, either via social disruption or by preventing bitcoin from improving * we don't want to ship code that causes people to fall out of consensus in the (hopefully unlikely) event that things don't go smoothly [0] In light of that, I think I'm leaning towards: * use BIP 8 with mandatory activation disabled in bitcoin core -- if you want to participate in enforcing mandatory activation, you'll need to recompile, or use a fork like bitcoin knots; however if mandatory activation occurs on the longest chain, you'll still follow that chain and enforce the rules. * be prepared to update the BIP 8 parameters to allow mandatory activation in bitcoin core if, after 9 months say, it's apparent that there aren't reasonable objections, there's strong support for activation, the vast majority of nodes have already updated to enforce the rules upon activation, and there's strong support for mandatory activation * change the dec-threshold proposal to be compatible with BIP 8, and keep it maintained so that it can be used if there seems to be widespread consensus for activation, but BIP 8 activation does not seem certain -- ie, as an extra contingency plan. * be prepared to support miners coordinating via BIP 91 either to bring activation forward in either BIP 8 or "decreasing threshold" or de-risk BIP 8 mandatory activation -- ie, an alternative contingency plan. This is more appropriate if we've found that users/miners have upgraded so that activation is safe; so it's a decision we can make later when we have more data, rather than having to make the decision early when we don't have enough information to judge whether it's safe or not. * (also, improve BIP 8 a bit more before deploying it -- I'm hoping for some modest changes, which is why "decreasing threshold" isn't already compatible with BIP 8) * (continue to ensure the underlying soft fork makes sense and is well implemented on its own merits) * (continue to talk to as many people as we can about the underlying changes and make sure people understand what's going on and that we've addressed any reasonable objections) I'm hopeful activating taproot will go smoothly, but I'm not 100% sure of it, and there are potentially many different ways in which things go wrong; so starting with something simple and being ready to adapt if/when we see things starting to go weird seems like a good approach to me. Cheers, aj [0] At least, that's how I'm phrasing some of the concerns that were expressed in, eg, https://github.com/bitcoin/bitcoin/pull/10428#issuecomment-303098925 https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-April/014152.html