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([2600:380:7045:ddda:2dc5:cf82:3470:54a0]) by smtp.gmail.com with ESMTPSA id x12sm8507291pff.48.2020.08.23.10.49.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 23 Aug 2020 10:49:36 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Eric Voskuil Mime-Version: 1.0 (1.0) Date: Sun, 23 Aug 2020 10:49:35 -0700 Message-Id: <27FE83C7-0269-4DEB-82E4-486FAFFA0DE5@voskuil.org> References: In-Reply-To: To: Matt Corallo X-Mailer: iPhone Mail (17G80) X-Mailman-Approved-At: Sun, 23 Aug 2020 17:51:05 +0000 Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Generalizing feature negotiation when new p2p connections are setup 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: Sun, 23 Aug 2020 17:49:38 -0000 > On Aug 21, 2020, at 15:16, Matt Corallo wrote: >=20 > =EF=BB=BFHmm, could that not be accomplished by simply building this into n= ew messages? eg, send "betterprotocol", if you see a verack and no "betterpr= otocol" from your peer, send "worseprotocol" before you send a "verack". >=20 > Matt >=20 >> On 8/21/20 5:17 PM, Jeremy wrote: >> As for an example of where you'd want multi-round, you could imagine a sc= enario where you have a feature A which gets bugfixed by the introduction of= feature B, and you don't want to expose that you support A unless you first= negotiate B. Or if you can negotiate B you should never expose A, but for o= ld nodes you'll still do it if B is unknown to them. This seems to imply a security benefit (I can=E2=80=99t discern any other ra= tionale for this complexity). It should be clear that this is no more than t= rivially weak obfuscation and not worth complicating the protocol to achieve= . >> An example of this would be (were it not already out without a feature ne= gotiation existing) WTXID/TXID relay. >> The SYNC primitve simply codifies what order messages should be in and wh= en you're done for a phase of negotiation offering something. It can be done= without, but then you have to be more careful to broadcast in the correct o= rder and it's not clear when/if you should wait for more time before respond= ing. >> On Fri, Aug 21, 2020 at 2:08 PM Jeremy > wrote: >> Actually we already have service bits (which are sadly limited) which a= llow negotiation of non bilateral feature >> support, so this would supercede that. >> -- >> @JeremyRubin