From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id C2C55A71 for ; Fri, 10 Nov 2017 01:32:08 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from ozlabs.org (ozlabs.org [103.22.144.67]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 3A78D196 for ; Fri, 10 Nov 2017 01:32:07 +0000 (UTC) Received: by ozlabs.org (Postfix, from userid 1011) id 3yY2ZX63xyz9t2R; Fri, 10 Nov 2017 12:32:04 +1100 (AEDT) From: Rusty Russell To: Date: Fri, 10 Nov 2017 12:01:14 +1030 Message-ID: <87lgjex6l9.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-2.3 required=5.0 tests=RCVD_IN_DNSWL_MED, RP_MATCHES_RCVD autolearn=disabled version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Christian Decker , Russell O'Connor Subject: [bitcoin-dev] Covenants through merkelized txids. X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 10 Nov 2017 01:32:08 -0000 Hi all, This is an alternative to jl2012's BIPZZZ (OP_PUSHTXDATA[1]). It riffs on the (ab)use of OP_CHECKSIGFROMSTACK that Russell[2] used to implement covenants[3]. I've been talking about it to random people for a while, but haven't taken time to write it up. The idea is to provide a OP_TXMERKLEVERIFY that compares the top stack element against a merkle tree of the current tx constructed like so[4]: TXMERKLE = merkle(nVersion | nLockTime | fee, inputs & outputs) inputs & outputs = merkle(inputmerkle, outputmerkle) input = merkle(prevoutpoint, nSequence | inputAmount) output = merkle(nValue, scriptPubkey) Many variants are possible, but if we have OP_CAT, this makes it fairly easy to test a particular tx property. A dedicated OP_MERKLE would make it even easier, of course. If we one day HF and add merklized TXIDs[5], we could also use this method to inspect the tx *being spent* (which was what I was originally trying to do). Thanks for reading! Rusty. [1] https://github.com/jl2012/bips/blob/vault/bip-0ZZZ.mediawiki [2] Aka Dr. "Not Rusty" O'Connor. Of course both of us in the same thread will probably break the internet. [3] https://blockstream.com/2016/11/02/covenants-in-elements-alpha.html [4] You could put every element in a leaf, but that's less compact to use: cheaper to supply the missing parts with OP_CAT than add another level. [5] Eg. use the high nVersion bit to say "make my txid a merkle".