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 1UsEpj-0003DT-Ak for bitcoin-development@lists.sourceforge.net; Thu, 27 Jun 2013 16:14:07 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.215.41 as permitted sender) client-ip=209.85.215.41; envelope-from=gmaxwell@gmail.com; helo=mail-la0-f41.google.com; Received: from mail-la0-f41.google.com ([209.85.215.41]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UsEph-0007VL-Im for bitcoin-development@lists.sourceforge.net; Thu, 27 Jun 2013 16:14:07 +0000 Received: by mail-la0-f41.google.com with SMTP id fn20so1059099lab.14 for ; Thu, 27 Jun 2013 09:13:58 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.152.87.234 with SMTP id bb10mr4580028lab.55.1372349638847; Thu, 27 Jun 2013 09:13:58 -0700 (PDT) Received: by 10.112.160.104 with HTTP; Thu, 27 Jun 2013 09:13:58 -0700 (PDT) In-Reply-To: <51CC6259.3060003@inf.ethz.ch> References: <51CC12A6.3090100@inf.ethz.ch> <51CC6259.3060003@inf.ethz.ch> Date: Thu, 27 Jun 2013 09:13:58 -0700 Message-ID: From: Gregory Maxwell To: Arthur Gervais Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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: 1UsEph-0007VL-Im Cc: Ghassan Karame , bitcoin-development@lists.sourceforge.net, Hubert Ritzdorf Subject: Re: [Bitcoin-development] Double-Spending Fast Payments in Bitcoin due to Client versions 0.8.1 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: Thu, 27 Jun 2013 16:14:07 -0000 On Thu, Jun 27, 2013 at 9:03 AM, Arthur Gervais wrote: > affecting the same Bitcoin version. However we think it is > complementary, since our reported problem has nothing to do with fees, > dust, nor is it necessary to send the two double-spending transaction at > the same time. In our setting, double-spending still works if the second > transaction is sent after minutes (and the first transaction has not yet > been included into a block). It works just the same for dust based or any other criteria that makes transactions non-standard=E2=80=94 including the double spending working if the second transaction is sent minutes after. Exactly the same code is executed and the same behavior observed for any case of a non-standard transaction being used to achieve inconsistent forwarding. > Our only intention is to raise the awareness for merchants who have to > accept zero-confirmation transactions. That is great and I'm certainly glad to see people doing that. Though take care it that your focus on signature encoding differences doesn't create a misunderstanding. This isn't only an issue with these particular versions: There is always mining and relay behavior inhomogeneity in the network. The level of inhomogeneity changes over time=E2=80=94 I believe its greatest when new reference client software tha= t changes IsStandard but it is never zero as there are large miners with customized acceptance rules (also mempool state also creates inhomogeneity). The greater inhomogeneity results in higher success rates which may be important since some service could conceivable only be profitable exploited with a high enough success rate.