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 DB3018B1 for ; Wed, 17 Aug 2016 03:02:56 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from erelay3.ox.registrar-servers.com (erelay3.ox.registrar-servers.com [192.64.117.2]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 4F9B8126 for ; Wed, 17 Aug 2016 03:02:56 +0000 (UTC) Received: from localhost (unknown [127.0.0.1]) by erelay1.ox.registrar-servers.com (Postfix) with ESMTP id 8EB0722088F4; Wed, 17 Aug 2016 03:02:55 +0000 (UTC) Received: from erelay1.ox.registrar-servers.com ([127.0.0.1]) by localhost (erelay.ox.registrar-servers.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id ONIstY8794iZ; Tue, 16 Aug 2016 23:02:54 -0400 (EDT) Received: from MTA-07.privateemail.com (unknown [10.20.150.170]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by erelay1.ox.registrar-servers.com (Postfix) with ESMTPS id 14B8F22088F3; Tue, 16 Aug 2016 23:02:54 -0400 (EDT) Received: from APP-06 (unknown [10.20.147.156]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by MTA-07.privateemail.com (Postfix) with ESMTPSA id 9984760034; Wed, 17 Aug 2016 03:02:53 +0000 (UTC) Date: Tue, 16 Aug 2016 23:02:53 -0400 (EDT) From: Johnson Lau Reply-To: Johnson Lau To: Gregory Maxwell , Russell O'Connor , Bitcoin Protocol Discussion , pete@petertodd.org Message-ID: <976728541.94211.1471402973613@privateemail.com> In-Reply-To: References: <1736097121.90204.1471369988809@privateemail.com> <201608161937.20748.luke@dashjr.org> <20160816194332.GA5888@fedora-21-dvm> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Medium X-Mailer: Open-Xchange Mailer v7.8.1-Rev18 X-Originating-Client: open-xchange-appsuite X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,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 Subject: Re: [bitcoin-dev] New BIP: Dealing with OP_IF and OP_NOTIF malleability in P2WSH 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: Wed, 17 Aug 2016 03:02:57 -0000 > On August 16, 2016 at 8:27 PM Russell O'Connor via bitcoin-dev wrote: > > Okay. > > I'm not really opposed to this BIP, but I am worried that fighting script malleability is a battle that can never be won; even leaving one avenue of malleability open is probably just as bad as having many avenues of malleability, so it just doesn't seem worthwhile to me. Not really. I think the goal is to protect as many common scripts as possible. For example: 1) BIP146 (Low S values signatures) will eliminate all malleability for P2WPKH 2) BIP146 + null dummy value for CHECKMULTISIG ("NULLDUMMY") will eliminate all malleability for simple multi-sig in P2WSH. This is particularly interesting since without NULLDUMMY, attackers are able to replace the dummy value with anything. 3) BIP146 + NULLDUMMY + minimal IF argument ("MINIMALIF") will eliminate malleability for any Lightening Network scripts that I'm aware of. With 3), 99.99% of segwit transactions in foreseeable future should be fully protected. The plan is to implement MINIMALIF as a relay policy first, and enforce the softfork after further risks assessment. This BIP serves as a warning to users for not using incompatible script. Peter Todd: > Having said that, a better approach may be a separate CHECKBOOLVERIFY opcode that fails unless the top item on the stack is a minimally encoded true or false value, to allow script writers to opt into this behavior; it's not always ideal. I believe all Lightening Network scripts (the only real users of IF/NOTIF in foreseeable future) are already compatible with MINIMALIF. It may not be a good idea for them to spend 1 more byte to get protected. If people want to have the original OP_IF behaviour, a simple way would be using "0NOTEQUAL IF". However, this works only if the argument is a valid number (also beware of MINIMALDATA rule in BIP62). To completely replicate the original behaviour, one may use: "DEPTH TOALTSTACK IFDUP DEPTH FROMALTSTACK NUMNOTEQUAL IF 2DROP {if script} ELSE DROP {else script} ENDIF" This is because we don't have a simple OP_CASTTOBOOL, and IFDUP is 1 of the 4 codes that perform CastToBool on top stack item (the others are VERIFY, IF, and NOTIF; and VERIFY can't be used here since it terminates the script with a False).