Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1Xds7W-0002BR-C7 for bitcoin-development@lists.sourceforge.net; Tue, 14 Oct 2014 02:45:54 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.213.179 as permitted sender) client-ip=209.85.213.179; envelope-from=gmaxwell@gmail.com; helo=mail-ig0-f179.google.com; Received: from mail-ig0-f179.google.com ([209.85.213.179]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1Xds7V-0001Dc-F5 for bitcoin-development@lists.sourceforge.net; Tue, 14 Oct 2014 02:45:54 +0000 Received: by mail-ig0-f179.google.com with SMTP id h18so12896805igc.12 for ; Mon, 13 Oct 2014 19:45:47 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.50.73.168 with SMTP id m8mr3286553igv.49.1413254747344; Mon, 13 Oct 2014 19:45:47 -0700 (PDT) Received: by 10.107.159.3 with HTTP; Mon, 13 Oct 2014 19:45:47 -0700 (PDT) In-Reply-To: References: Date: Tue, 14 Oct 2014 02:45:47 +0000 Message-ID: From: Gregory Maxwell To: Pieter Wuille Content-Type: text/plain; charset=UTF-8 X-Spam-Score: -1.6 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (gmaxwell[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1Xds7V-0001Dc-F5 Cc: Bitcoin Dev Subject: Re: [Bitcoin-development] Malleable booleans X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 14 Oct 2014 02:45:54 -0000 On Tue, Oct 14, 2014 at 2:34 AM, Pieter Wuille wrote: > Hi all, > > while working on a BIP62 implementation I discovered yet another type > of malleability: the interpretation of booleans. > > Any byte array with non-zero bytes in it (ignoring the highest bit of > the last byte, which is the sign bit when interpreting as a number) is > interpreted as true, anything else as false. Other than numbers, > they're not even restricted to 4 bytes. Worse, the code for dealing > with booleans is not very consistent: OP_BOOLAND and OP_BOOLOR first > interpret their arguments as numbers, and then compare them to 0 to > turn them into boolean values. > > This means that scripts that use booleans as inputs will be inherently > malleable. Given that that seems actually useful (passing in booleans > to guide some OP_IF's during execution of several alternatives), I > would like to change BIP62 to also state that interpreted booleans > must be of minimal encoded size (in addition to numbers). > > Any opinions for or against? An argument against is that you can currently do something like this: OP_DUP OP_IF OP_HASH160 PUSH OP_EQUALVERIFY OP_ELSE OP_CHECKSIGVERIFY OP_ENDIF E.g. if your input is non-zero you're giving a hash, if it's zero you're skipping that and running another branch. Of course you could just encode your script another way... but by that same logic you can 1 OP_QUALVERIFY to bool-ize any input in the true path. The inconsistency in handling makes it more likely that script authors will screw up with bad (for them) consequences, however. [I just asked pieter out of band to clarify if he means "minimal encoded size", or must be 0 or 1 minimally encoded... as the former doesn't fix the malleability, but the later is more disruptive]