Return-Path: Received: from smtp4.osuosl.org (smtp4.osuosl.org [IPv6:2605:bc80:3010::137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 59894C0032 for ; Mon, 2 Oct 2023 15:10:22 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 2E47F41E41 for ; Mon, 2 Oct 2023 15:10:22 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp4.osuosl.org 2E47F41E41 X-Virus-Scanned: amavisd-new at osuosl.org X-Spam-Flag: NO X-Spam-Score: -1.902 X-Spam-Level: X-Spam-Status: No, score=-1.902 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id IXfmEMUSCjH1 for ; Mon, 2 Oct 2023 15:10:18 +0000 (UTC) Received: from cerulean.erisian.com.au (azure.erisian.com.au [172.104.61.193]) by smtp4.osuosl.org (Postfix) with ESMTPS id 7015E41ADE for ; Mon, 2 Oct 2023 15:10:18 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp4.osuosl.org 7015E41ADE Received: from aj@azure.erisian.com.au by cerulean.erisian.com.au with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1qnKYm-0006fh-H7; Tue, 03 Oct 2023 01:10:15 +1000 Received: by email (sSMTP sendmail emulation); Tue, 03 Oct 2023 01:10:08 +1000 Date: Tue, 3 Oct 2023 01:10:08 +1000 From: Anthony Towns To: Johan =?iso-8859-1?Q?Tor=E5s?= Halseth , Bitcoin Protocol Discussion Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam_score: -0.0 X-Spam_bar: / Subject: Re: [bitcoin-dev] MATT: [demo] Optimistic execution of arbitrary programs 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: Mon, 02 Oct 2023 15:10:22 -0000 On Fri, Sep 29, 2023 at 03:14:25PM +0200, Johan Torås Halseth via bitcoin-dev wrote: > TLDR; Using the proposed opcode OP_CHECKCONTRACTVERIFY and OP_CAT, we > show to trace execution of the program `multiply` [1] and challenge > this computation in O(n logn) on-chain transactions: "O(n log n)" sounds wrong? Isn't it O(P + log(N)) where P is the size of the program, and N is the number of steps (rounded up to a power of 2)? You say: > node = h( start_pc|start_i|start_x|end_pc|end_i|end_x|h( h(sub_node1)|h(sub_node2) ) But I don't think that works -- I think you want to know h(sub_node1) and h(sub_node2) directly, so that you can compare them to the results you get if you run the computation, and choose the one that's incorrect. Otherwise you've got a 50/50 chance of choosing the subnode that's actually correct, and you'll only be able to prove a mistake with 1/2**N odds? Not a big change, it just becomes 32B longer (and drops some h()s): node = start_pc|start_i|start_x|end_pc|end_i|end_x|h(sub_node1)|h(sub_node2) leaf = start_pc|start_i|start_x|end_pc|end_i|end_x|null I'm not seeing what forces the prover to come up with a balanced state tree -- if they don't have to have a balanced tree, then I think there are many possible trees for the same execution trace, and again it would become easy to hide an error somewhere the challenger can't find. Adding a "start_stepcount" and "end_stepcount" would probably remedy that? There seems to be an error in the "what this would look like for 4 state transitions" diagram -- the second node should read "0|0|2 -> 0|1|4" (combining its two children), not "0|0|2 -> 1|0|2" matching its left child. I'm presuming that the counterparty verifies they know the program (ie, all the leaves in the contract taptree) before agreeing to the contract in the first place. I think that's fine. Cheers, aj