From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-2.v43.ch3.sourceforge.com ([172.29.43.192] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1Z25Np-0005f7-TV for bitcoin-development@lists.sourceforge.net; Mon, 08 Jun 2015 22:19:05 +0000 Received-SPF: pass (sog-mx-2.v43.ch3.sourceforge.com: domain of petertodd.org designates 62.13.148.154 as permitted sender) client-ip=62.13.148.154; envelope-from=pete@petertodd.org; helo=outmail148154.authsmtp.co.uk; Received: from outmail148154.authsmtp.co.uk ([62.13.148.154]) by sog-mx-2.v43.ch3.sourceforge.com with esmtp (Exim 4.76) id 1Z25No-0004FN-DM for bitcoin-development@lists.sourceforge.net; Mon, 08 Jun 2015 22:19:05 +0000 Received: from mail-c235.authsmtp.com (mail-c235.authsmtp.com [62.13.128.235]) by punt15.authsmtp.com (8.14.2/8.14.2/) with ESMTP id t58MIufZ051033; Mon, 8 Jun 2015 23:18:56 +0100 (BST) Received: from muck (bas3-cooksville17-1176329630.dsl.bell.ca [70.29.93.158]) (authenticated bits=128) by mail.authsmtp.com (8.14.2/8.14.2/) with ESMTP id t58MIox1007838 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO); Mon, 8 Jun 2015 23:18:53 +0100 (BST) Date: Mon, 8 Jun 2015 18:18:43 -0400 From: Peter Todd To: "Raystonn ." Message-ID: <20150608221843.GA4275@muck> References: <5574E39C.3090904@thinlink.com> <7E7DF414-6DDB-48A6-9199-D6883209B67D@newcastle.ac.uk> <20150608214443.GC19826@muck> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Q68bSM7Ycu6FN28Q" Content-Disposition: inline In-Reply-To: X-Server-Quench: 5a0627b5-0e2c-11e5-b396-002590a15da7 X-AuthReport-Spam: If SPAM / abuse - report it at: http://www.authsmtp.com/abuse X-AuthRoute: OCd2Yg0TA1ZNQRgX IjsJECJaVQIpKltL GxAVKBZePFsRUQkR aQdMdgoUEkAaAgsB AmMbWVdeUVV7XGY7 bApPbwxDa0lQXgBi T01BRU1TWkFtCWF4 WVYfUhl1fwZONnxw bUJmEHUKXEJ4chR4 X04BFz4bZGY1bX1N U0leagNUcgZDfk5E bwQuUz1vNG8XDQg5 AwQ0PjZ0MThBJSBS WgQAK04nCWAGAXY1 WwwLFjZnHEEIQTky IR0rJhYVGkpZKkIu PF09WFscUVcJDQlD A0BKBk5VKkIKXSsh AA8IFWIEFyVFTCsZ HgchJARBCSBTXSwQ H1NMTlkGFz9MWyoA QTlUUys2EBA1J09I ei4bNgoyABwsRlJJ DBgTWiMh X-Authentic-SMTP: 61633532353630.1023:706 X-AuthFastPath: 0 (Was 255) X-AuthSMTP-Origin: 70.29.93.158/587 X-AuthVirus-Status: No virus detected - but ensure you scan with your own anti-virus system. 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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 SPF_PASS SPF: sender matches SPF record -0.0 AWL AWL: Adjusted score from AWL reputation of From: address X-Headers-End: 1Z25No-0004FN-DM Cc: Bitcoin Dev , "Patrick Mccorry \(PGR\)" Subject: Re: [Bitcoin-development] New attack identified and potential solution described: Dropped-transaction spam attack against the blocksize limit 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, 08 Jun 2015 22:19:05 -0000 --Q68bSM7Ycu6FN28Q Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jun 08, 2015 at 03:01:34PM -0700, Raystonn . wrote: > >There will always be a blocksize limit based on technological > >considerations - the network has a finite bandwidth limit. >=20 > A bandwidth limit is not the same as a blocksize limit. Bandwidth > is unique to every individual. Miners in China have different > bandwidth and connectivity than miners in the U.S., for example. > But the block size limit is dictated for eveyone. They are not > comparable. Bitcoin is a global consensus system - if you're bandwidth isn't sufficient to keep up you are not part of the consensus. The blocksize limit *is* what determines the minimum bandwidth required to stay in consensus. > >Without a blocksize limit the attacker would just flood the > >network until the bandwidth usage became so great that consensus > >would fail, rendering Bitcoin both worthless, and insecure. >=20 > No, with no blocksize limit, a spammer would would flood the network > with transactions until they ran out of money. Meanwhile, everyone > would jump on board trying to mine the blocks to collect the fees > from the spammers. It could be one of the greatest transfers of > wealth ever. Bitcoin infrastructure would build up to handle the > required bandwidth, paid for by the very entity spamming the > network. Bitcoin would flourish, growing wildly as long as the fees > kept coming. This is antifragility at its best. Again, in your scenario if the bandwidth consumed by those transactions was sufficiently high, the network would collapse because consensus would fail. Why wouldn't that bandwidth be high enough to cause that collapse? Because of the blocksize limit! (combined with an intelligent mempool that increases the minimum fee/KB appropriately - we don't have that yet) > >The worst an attacker flooding the network with transactions with > >a blocksize limit can do is raise costs, without harming security. >=20 > No, at attacker flooding the network with transactions with a > blocksize limit can keep their fees high enough that perhaps 1% of > transactions coming from real end-users go through. At this point > everyone would give up on Bitcoin as it would become completely > unusable. The BTCUSD market would tank, making it even easier to > pay the transaction fees to keep real transactions out of blocks, as > it would continue to become cheaper and eventually cost-free to > obtain the bitcoin fees through market purchase. I already did the math for you on that: the maximum transaction fee you'd see in that kind of attack is around $2.5 USD/tx. That definitely is not high enough to make Bitcoin non-viable - I personally could easily afford fees like that for about 90% of my transactions this year by value, as I mainly use Bitcoin to get paid by my clients around the world. In fact, just today O'Reilly paid $15 USD to send me a wire transfer for expenses related to a conference I was invited too. A much more realistic transaction flood scenario - one that didn't raise serious questions about whether or not the attacker could afford to 51% attack Bitcoin - would raise tx fees to something more like $0.25/tx --=20 'peter'[:-1]@petertodd.org 0000000000000000127ab1d576dc851f374424f1269c4700ccaba2c42d97e778 --Q68bSM7Ycu6FN28Q Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- iQGrBAEBCACVBQJVdhTAXhSAAAAAABUAQGJsb2NraGFzaEBiaXRjb2luLm9yZzAw MDAwMDAwMDAwMDAwMDAxMjdhYjFkNTc2ZGM4NTFmMzc0NDI0ZjEyNjljNDcwMGNj YWJhMmM0MmQ5N2U3NzgvFIAAAAAAFQARcGthLWFkZHJlc3NAZ251cGcub3JncGV0 ZUBwZXRlcnRvZC5vcmcACgkQwIXyHOf0udyd1wf+KvozUrU/wVjTMISz/JTpJD86 B6C72QrFJOkqEuraVLGwtYpl3aSOF4Cc6abiyzqg7TYnyTgI8tf0BZM0ZxHPV0Wb yqBklusrCj7kIuSoHGmaYHPkK+d9KxqmROuM1NtKqZNcVoxemyheQ55HeH8umj/I RjlE5UsjmYaVCM+/A6z0qwoG4DOQBVlJ4UPgOITlbYbrw0Rbko9D2kyP6lXUIdyY RTPCAZHr/oQxBE42BzD7EYzgsxanh38xeTE81+W7WIzQdBGsIHY9LQBWNZOHQRJo W5/wiaur40kXXjoS5rSDLThgAztN9tmEU0kJOly7JUrxhpjunbGf/Qk/DwEhBg== =Edzm -----END PGP SIGNATURE----- --Q68bSM7Ycu6FN28Q--