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-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1VdL78-0001aW-78 for bitcoin-development@lists.sourceforge.net; Mon, 04 Nov 2013 14:26:46 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of petertodd.org designates 62.13.148.111 as permitted sender) client-ip=62.13.148.111; envelope-from=pete@petertodd.org; helo=outmail148111.authsmtp.net; Received: from outmail148111.authsmtp.net ([62.13.148.111]) by sog-mx-1.v43.ch3.sourceforge.com with esmtp (Exim 4.76) id 1VdL76-0003ms-GX for bitcoin-development@lists.sourceforge.net; Mon, 04 Nov 2013 14:26:46 +0000 Received: from mail-c235.authsmtp.com (mail-c235.authsmtp.com [62.13.128.235]) by punt8.authsmtp.com (8.14.2/8.14.2) with ESMTP id rA4EQWJ5000477; Mon, 4 Nov 2013 14:26:32 GMT Received: from petertodd.org (petertodd.org [174.129.28.249]) (authenticated bits=128) by mail.authsmtp.com (8.14.2/8.14.2/) with ESMTP id rA4EQLBS063523 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO); Mon, 4 Nov 2013 14:26:24 GMT Date: Mon, 4 Nov 2013 09:26:21 -0500 From: Peter Todd To: Mike Hearn , Ittay Eyal Message-ID: <20131104142621.GA2190@petertodd.org> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="a8Wt8u1KmwUX3Y2C" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Server-Quench: 15d8f42b-455d-11e3-b802-002590a15da7 X-AuthReport-Spam: If SPAM / abuse - report it at: http://www.authsmtp.com/abuse X-AuthRoute: OCd2Yg0TA1ZNQRgX IjsJECJaVQIpKltL GxAVKBZePFsRUQkR aQdMdgYUFloCAgsB AmUbWlBeUlt7W2Y7 ag1VcwRfa1RMVxto VEFWR1pVCwQmQ20F c39iIHpycQZDen0+ ZE9kVnQVXUEufRB5 QBxJEWgDMXphaTUc TRJQdwFJcANIexZF O1F6ACIKLwdSbGoL NQ4vNDcwO3BTJTpY RgYVKF8UXXNDNyMg QFUNEDMiB0QZSil7 Kh0gJ0RUFk8aMU81 N1ZJ X-Authentic-SMTP: 61633532353630.1023:706 X-AuthFastPath: 0 (Was 255) X-AuthSMTP-Origin: 174.129.28.249/587 X-AuthVirus-Status: No virus detected - but ensure you scan with your own anti-virus system. 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[URIs: petertodd.org] X-Headers-End: 1VdL76-0003ms-GX Cc: Bitcoin Dev Subject: Re: [Bitcoin-development] Auto-generated miner backbone 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: Mon, 04 Nov 2013 14:26:46 -0000 --a8Wt8u1KmwUX3Y2C Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Nov 04, 2013 at 12:26:30PM +0100, Mike Hearn wrote: > W.R.T. this paper and the oft-discussed miner backbone, >=20 > http://arxiv.org/pdf/1311.0243v1.pdf >=20 > I'm wondering about an alternative protocol change that perhaps has less > subtle implications than their suggested change. Rather than address the > problem by assuming the network is full of sybil nodes and changing the > rules for selecting the chain to build on, how about if we wrote code to > automatically build a miner backbone by having IP addresses of nodes > embedded into coinbases, then having any bitcoind that is creating work > automatically connect to IPs that appeared in enough recent blocks? >=20 > It feels like this should be achievable with a few days of solid coding a= nd > a couple of new command line flags, and the impact is much easier to reas= on > about than a fundamental rule change like the one proposed by the paper. Actually on further reflection this idea will make the attack described in the paper easier to carry out, rather than harder. I think where you're misunderstanding originates is the description of this attack as requiring a sybil attack on the network - you see this underlying sybil as one of numerical advantage, when it's actually one of *informational* advantage. Remember that the selfish miner strategy outlined in the paper is essentially a way to use knowledge of what blocks miners will be mining on, from the "first seen" rule, and the ability to broadcast blocks you have mined more widely than other miners. That knowledge and ability is then used in conjunction with a small lead (obtainable by chance) to outpace the rest of the network. By making all miners easily identifiable you make gaining that informational and broadcast capability easier to obtain rather than harder. The attacker now only needs to connect to every identified miner with especially fast nodes. With judicious use of DoS attacks and low latency they can still gain the informational and broadcast "upper hand" over other miners and carry out the attack. Where the paper goes wrong is they don't recognize the fundemental nature of the strategy being based on an informational advantage. Their "pick a random side of the fork" strategy may work to some extent, but it's incomplete and isn't necessarily rational for the miners individually. The correct, and rational, approach for a miner is to always mine to extend the block that the majority of hashing power is trying to extend. The current relay rules don't give you that information at all, but they can if we do two things: 1) Relay all blocks that meet the PoW target. (as suggested in the paper) 2) Relay block headers that nearly meet the PoW target. Mining strategy is now to mine to extend the first block you see, on the assumption that the earlier one probably propagated to a large portion of the total hashing power. But as you receive "near-blocks" that are under the PoW target, use them to estimate the hashing power on each fork, and if it looks like you are not on the majority side, switch. This very effectively defeats the paper's selfish-miner strategy, as all miners will very quickly be mining on the block that truly has the majority of hashing power trying to extend it. This is also a better overall outcome, because it puts the 51% attack threshhold back at 51% --=20 'peter'[:-1]@petertodd.org 0000000000000004ee9bb13b022c412d75692b5e85454013c53f89e5d6fa8c69 --a8Wt8u1KmwUX3Y2C Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQEcBAEBCAAGBQJSd66NAAoJEBmcgzuo5/CFAIcH/2M7X68XC4hQj77H6yPslS03 lYcShJL1P8Ya5WyPgDuxF5coICDlI6EN0au+peNqr1Vby5jVfFrYByVeVWWH16vf b5yLYwfV9YglGr8Oavnq7ywMvWGW1luoZrOI+qVH6crdHiD7N2DG3XG8NHd0n/+h 1VziCoXgeoHq9MX3HyRzqh+igTgS1KzGskG/e10TTG0txjbrEsA08zETkALfdx8W 8VBbeYMmrxgaQb2MsJc9lsyBQtE//lgue03Eiab2y3XHmRvtUy3rFaRvTRoa9VLt CLEWXCk8+5rDgIQTmo/CgRK8Q62jbMnZya1LLCd5JZxLkZHhIY0OomSNr13u82w= =MSPd -----END PGP SIGNATURE----- --a8Wt8u1KmwUX3Y2C--