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 77100ACD for ; Sun, 6 Oct 2019 08:47:06 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40136.protonmail.ch (mail-40136.protonmail.ch [185.70.40.136]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 8982A27B for ; Sun, 6 Oct 2019 08:47:04 +0000 (UTC) Date: Sun, 06 Oct 2019 08:46:59 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1570351621; bh=Bueb3/oO+DK2pt6F0p29BaQTcY1NUIK/0qtI0cUElQg=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References: Feedback-ID:From; b=jJMlrWgb7kFbQGNYDgrDPaAwglU0Lce6qTcXK/8nJLhDRQEW0GpYHOFjli31Atxlx twGJVvIsMZDSge563nSwd6Ss6853QJ19EohmJpRO7V7NbpCymbH3KNX2V55jr//Pbv XkXyqh4Tj6rjlaDv6YD3jknI3HQc9eaonAqZO6dk= To: Peter Todd From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: <20191005154902.ck236q65xha25ore@petertodd.org> References: <87wodp7w9f.fsf@gmail.com> <20191001155929.e2yznsetqesx2jxo@erisian.com.au> <20191004111536.w7snbgpoe27xutfu@petertodd.org> <20191005154902.ck236q65xha25ore@petertodd.org> Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DOS_RCVD_IP_TWICE_B, FREEMAIL_FROM, FROM_LOCAL_NOVOWEL, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Bitcoin Protocol Discussion , "lightning-dev@lists.linuxfoundation.org" Subject: Re: [bitcoin-dev] [Lightning-dev] OP_CAT was Re: Continuing the discussion about noinput / anyprevout 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: Sun, 06 Oct 2019 08:47:06 -0000 Good morning Peter, Jeremy, and lists, > On Fri, Oct 04, 2019 at 11:40:53AM -0700, Jeremy wrote: > > > Interesting point. > > The script is under your control, so you should be able to ensure that = you > > are always using a correctly constructed midstate, e.g., something like= : > > scriptPubKey: <-1> OP_SHA256STREAM DEPTH OP_SHA256STREAM <-2> > > OP_SHA256STREAM > > OP_EQUALVERIFY > > would hash all the elements on the stack and compare to a known hash. > > How is that sort of thing weak to midstateattacks? > > Obviously with care you can get the computation right. But at that point = what's > the actual advantage over OP_CAT? > > We're limited by the size of the script anyway; if the OP_CAT output size= limit > is comparable to that for almost anything you could use SHA256STREAM on y= ou > could just as easily use OP_CAT, followed by a single OP_SHA256. Theoretically, `OP_CAT` is less efficient. In cases where the memory area used to back the data cannot be resized, new= backing memory must be allocated elsewhere and the existing data copied. This leads to possible O( n^2 ) behavior for `OP_CAT` (degenerate case wher= e we add 1 byte per `OP_CAT` and each time find that the memory area curren= tly in use is exactly fitting the data and cannot be resized in-place). `OP_SHASTREAM` would not require new allocations once the stream state is i= n place and would not require any copying. This may be relevant in considering the cost of executing `OP_CAT`. Admittedly a sufficiently-limited maximum `OP_CAT` output would be helpful= in reducing the worst-case `OP_CAT` behavior. The question is what limit would be reasonable. 64 bytes feels too small if one considers Merkle tree proofs, due to mentio= ned issues of lack of typechecking. Regards, ZmnSCPxj > > -------------------------------------------------------------------------= ---------------------------------------------------------------------------= ---------------------------------------------------------------------------= ---------------------------------------------------------------------------= ---------------------------------------- > > https://petertodd.org 'peter'[:-1]@petertodd.org > > Lightning-dev mailing list > Lightning-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev