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-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1VdnbF-0006Ac-J6 for Bitcoin-development@lists.sourceforge.net; Tue, 05 Nov 2013 20:51:45 +0000 Received: from tapuz.safe-mail.net ([213.8.161.230]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76) id 1Vdnb4-0007aX-0m for Bitcoin-development@lists.sourceforge.net; Tue, 05 Nov 2013 20:51:45 +0000 Received: by tapuz.safe-mail.net with Safe-mail (Exim 4.63) (envelope-from ) id 1Vdnau-0004Vf-5i for Bitcoin-development@lists.sourceforge.net; Tue, 05 Nov 2013 15:51:24 -0500 Received: from pc ([37.221.160.203]) by Safe-mail.net with https Date: Tue, 5 Nov 2013 15:51:24 -0500 From: colj@Safe-mail.net To: Bitcoin-development@lists.sourceforge.net X-SMType: Regular X-SMRef: N1-9eAtMHauq2 Message-Id: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-SMSignature: lw8fbDC924d2oC6n83J8tMlQ+NXG+UjHuVS6sDBhKlYlciw5BIXz54FX1msnmgVX JCpzftsuvVvcn+gJ0jJWVh+Q22K2ULriaAfnDlWcqhbfWqUo8n/cnHco3kJRViih 67epjLLhP14YmWxShs1ZZ3NJvDmdNBFb4JS0cWdvsBs= X-Spam-Score: -0.1 (/) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (colj[at]safe-mail.net) -0.0 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [URIs: safe-mail.net] 0.0 MIME_QP_LONG_LINE RAW: Quoted-printable line longer than 76 chars -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: 1Vdnb4-0007aX-0m Subject: [Bitcoin-development] Possible Solution To SM Attack 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, 05 Nov 2013 20:51:45 -0000 Preliminary: Alice has the ability to hear of a block before all other miners do. The Problem: Say Alice built a block, A1, from previous block 0. She doesn't let other miners = know about it. She then works on A2 with previous block A1. Bob on the other = hand is still working on B1 with previous block 0. Bob now finds a block and = he broadcasts it. The assumption here is Alice will be the first miner to hear = of this block and she will send her previously mined block, A1, to all other = miners. By the time Bobs block arrives to other miners majority of them will = already have received Block A1 and Bobs block will most likely be orphaned. = Alice revealed her block, A1, only when Bob broadcast his block. This means = she has been mining on block A2 with previous block A1 for longer than any = other miner thus gaining an advantage without increasing her hash rate. What We Know: Alice has gained an advantage with time. She mines longer on the valid block. In order for this attack to work Alice must reveal her previously mined block = as late as possible, gaining her the most time spent working on the valid block. = Since she has such good view of the Bitcoin network she can wait until a miner = finds a block to release her previously mined block. The most obvious sign of this attack taking place is the timing. A miner will = receive a block and very quickly hear of another block both built from the = same previous block. The block that a miner hears first is the one which will be mined on. Possible Solution: If N amount of blocks built of the same previous block are received within = a time frame of T mine on the block with the lowest hash. Logic: In order for Alice to pull of this attack she not only has to propagate her = blocks first she must also ensure her blocks are of the smallest hash. Alice would now have to decrease her target to pull of this attack. Since she = has a lower target it will take her longer to find a valid block negating her = time advantage. colj