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[103.168.172.148]) by gmr-mx.google.com with ESMTPS id d9443c01a7336-2a3e4776e6bsi2035555ad.10.2026.01.08.00.30.21 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jan 2026 00:30:21 -0800 (PST) Received-SPF: pass (google.com: domain of sjors@sprovoost.nl designates 103.168.172.148 as permitted sender) client-ip=103.168.172.148; Received: from phl-compute-03.internal (phl-compute-03.internal [10.202.2.43]) by mailfout.phl.internal (Postfix) with ESMTP id 222E5EC00C4; Thu, 8 Jan 2026 03:30:21 -0500 (EST) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Thu, 08 Jan 2026 03:30:21 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefgedrtddtgddutdehgeekucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurheptggguffhjgffvefgkfhfvffosehtqhhmtdhhtddvnecuhfhrohhmpefujhhorhhs ucfrrhhovhhoohhsthcuoehsjhhorhhssehsphhrohhvohhoshhtrdhnlheqnecuggftrf grthhtvghrnhepueegffektddutdfgvdfhjeehveefjeffuefghfdtteefieekvdfhtefg jeeiteejnecuffhomhgrihhnpehgihhthhhusgdrtghomhdpshhtrggtkhgvgigthhgrnh hgvgdrtghomhdptdehqdhmihhnihhnghdqphhrohhtohgtohhlrdhmugdpuggvlhhvihhn ghgsihhttghoihhnrdhorhhgpdgsihhttghoihhnrdhithenucevlhhushhtvghrufhiii gvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpehsjhhorhhssehsphhrohhvohhoshht rdhnlhdpnhgspghrtghpthhtohepfedpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtoh eprghnthhoihhnvgdrrhhirghrugesghhmrghilhdrtghomhdprhgtphhtthhopegsihht tghoihhnuggvvhesghhoohhglhgvghhrohhuphhsrdgtohhmpdhrtghpthhtohepuggrrh hoshhiohhrsehprhhothhonhhmrghilhdrtghomh X-ME-Proxy: Feedback-ID: ie5e042df:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 8 Jan 2026 03:30:18 -0500 (EST) Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.300.41.1.7\)) Subject: Re: [bitcoindev] Addressing remaining points on BIP 54 From: Sjors Provoost In-Reply-To: <05f5b0ee-b487-4733-9860-ac0705b6b901n@googlegroups.com> Date: Thu, 8 Jan 2026 15:30:05 +0700 Cc: Bitcoin Development Mailing List , Antoine Poinsot Message-Id: <9C946151-D6DD-4CB7-B524-15FD9F625D9D@sprovoost.nl> References: <05f5b0ee-b487-4733-9860-ac0705b6b901n@googlegroups.com> To: Antoine Riard X-Mailer: Apple Mail (2.3864.300.41.1.7) X-Original-Sender: sjors@sprovoost.nl X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@sprovoost.nl header.s=fm3 header.b=oAaJvJl+; dkim=pass header.i=@messagingengine.com header.s=fm2 header.b=gbj2vrXE; spf=pass (google.com: domain of sjors@sprovoost.nl designates 103.168.172.148 as permitted sender) smtp.mailfrom=sjors@sprovoost.nl; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=sprovoost.nl Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -0.8 (/) Hello Riard, > Thanks for the update. If I'm understanding correctly Luke's concern, > currently the coinbase's scriptSig is used to store an extranonce. One > has to observe first there is no consensus limit on the size of a > transaction, which holds for the coinbase tx too, a fortiori there is > no limit on the extranonce size a miner could fit in the scriptSig. The coinbase scriptSig is limited to 100 bytes [0]. Some speculation as to why [1]. The main issue I see is complexity of implementation. The nLockTime is always the last 4 bytes of a transaction, so an ASIC can roll it without having to understand anything about serialisation. The scriptSig OTOH is variable length, so it needs to read the length byte in order to figure out which 4 bytes are at the end. The pool or proxy then also needs to ensure those 4 bytes are pre-initialised*. The approach suggested by Towns [4] of appending a 0-sat OP_RETURN output with padding so a 4-byte nonce lands in the final 64-byte SHA256 chunk is probably better, but not because like nLockTime it has a small hashing midstate benefit. It's easier to implement. Compared to varying the end of the scriptSig, this can be easier for an ASIC because it can update a fixed 4-byte field at a known offset from the end, rather than having to parse variable-length fields (notably the scriptSig length) to locate the bytes to roll. I think that extra complexity is doable and justifiable, but I've never built an ASIC. Note that today Stratum v1 simply splits the scriptSig [5] into two parts, as does Stratum v2 [3], but presumably that's all done by the control board and it makes sense to want to push rolling functionally into the ASIC silicon, where even simple concatenation might be too involved - but updating bytes at known positions is easy. > The point being made is that the nLocktime field of the coinbase > transaction could be used as a more efficient extra nonce due to > the positional location of nLocktime in a serialized coinbase being > one of the latest message block to be processed [0]. > > Nothing prevent a miner in already doing this and draw a speed advantage > from the diminished computational work. I have not looked into CGminer code > or one of its derivative forks, if there is an implemented option to do that, > but yes there could be non-published existing mining firmware doing it. IIUC, > BIP54 would nullify this theoretical "speed advantage" for all miners. I don't think there's currently a speed advantage, so I wouldn't expect to observe this behaviour in the wild just yet. The combination of rolling nVersion (BIP310) [2] and updating nTime every second, works fine up to 280 TH/s. Beyond that an ASIC will need to touch the coinbase. - Sjors [0] https://github.com/bitcoin/bitcoin/blob/v30.1/src/consensus/tx_check.cpp#L47-L51 [1] https://bitcoin.stackexchange.com/questions/35455/why-bother-having-limitations-on-bitcoin-coinbase-transaction-scriptsigs [2] https://github.com/bitcoin/bips/blob/master/bip-0310.mediawiki [3] https://github.com/stratum-mining/sv2-spec/blob/main/05-Mining-Protocol.md#511-standard-job [4] https://delvingbitcoin.org/t/great-consensus-cleanup-revival/710/88?u=sjors [5] https://en.bitcoin.it/wiki/Stratum_mining_protocol#mining.notify * = otherwise the ASIC needs to know how to extend it, know that it can't be more than 100 bytes, and that it can't touch the BIP34 part, or really any subsequent bytes that a future soft fork might constrain -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/9C946151-D6DD-4CB7-B524-15FD9F625D9D%40sprovoost.nl.