From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-1.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1Qp4DH-0003da-Aa for bitcoin-development@lists.sourceforge.net; Thu, 04 Aug 2011 20:08:15 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.216.182 as permitted sender) client-ip=209.85.216.182; envelope-from=gmaxwell@gmail.com; helo=mail-qy0-f182.google.com; Received: from mail-qy0-f182.google.com ([209.85.216.182]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1Qp4DF-000119-69 for bitcoin-development@lists.sourceforge.net; Thu, 04 Aug 2011 20:08:15 +0000 Received: by qyk9 with SMTP id 9so1294717qyk.13 for ; Thu, 04 Aug 2011 13:08:07 -0700 (PDT) MIME-Version: 1.0 Received: by 10.229.2.155 with SMTP id 27mr994740qcj.216.1312488487761; Thu, 04 Aug 2011 13:08:07 -0700 (PDT) Received: by 10.229.3.141 with HTTP; Thu, 4 Aug 2011 13:08:07 -0700 (PDT) In-Reply-To: <201108042042.55214.andyparkins@gmail.com> References: <201108041423.14176.andyparkins@gmail.com> <201108041922.16956.andyparkins@gmail.com> <1312483196.3109.38.camel@Desktop666> <201108042042.55214.andyparkins@gmail.com> Date: Thu, 4 Aug 2011 16:08:07 -0400 Message-ID: From: Gregory Maxwell To: Andy Parkins 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: 1Qp4DF-000119-69 Cc: bitcoin-development@lists.sourceforge.net Subject: Re: [Bitcoin-development] Double spend detection to speed up transaction trust 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, 04 Aug 2011 20:08:15 -0000 On Thu, Aug 4, 2011 at 3:42 PM, Andy Parkins wrote: > On Thursday 04 August 2011 19:39:56 Matt Corallo wrote: > >> But why? It results in slightly more network traffic which is exactly >> what we don't want, and it adds yet another message people have to know >> about. > > "Slightly" is an understatement. =C2=A0It add more network traffic for ev= ery > double spend attempt. =C2=A0Which don't happen very often. But they can be trivially generated on demand, and potentially result in unbounded flooding. Even if you carefully don't duplicate an announcement I can easily generate an unlimited number of double-spends for the network to flood. The normal anti-DDOS logic doesn't work because there can be no additional proof-of-workish costs for the double spend (they'd share whatever anti-ddos fees the first txn had). This is somewhat soluble, I guess. Rather than NAK the transaction the way it would work is propagating conflicts on each of the conflicted inputs. "I've seen at least two transactions recently trying to spend input X, here is proof: (two txn IDs)". Even if there are more spends of that input you don't need to hear about them, knowing about two spends of an input is enough to consider that input (and perhaps all inputs with an identical script to that one) temporarily suspect. Though it would have to be done input by input. This might be an interesting feature if not for the fact that the software already waits a fair number of confirms before considering something confirmed. Of course, a sybil can just filter these messages diminishing their usefulness. I suppose I could add this as a (7) to this list: https://bitcointalk.org/index.php?topic=3D28565.msg359948#msg359948