From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-3.v43.ch3.sourceforge.com ([172.29.43.193] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1RTCdn-0001ti-OG for bitcoin-development@lists.sourceforge.net; Wed, 23 Nov 2011 13:13:31 +0000 Received-SPF: pass (sog-mx-3.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.214.47 as permitted sender) client-ip=209.85.214.47; envelope-from=andyparkins@gmail.com; helo=mail-bw0-f47.google.com; Received: from mail-bw0-f47.google.com ([209.85.214.47]) by sog-mx-3.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1RTCdk-0003X7-0F for bitcoin-development@lists.sourceforge.net; Wed, 23 Nov 2011 13:13:31 +0000 Received: by bkbzs2 with SMTP id zs2so1582875bkb.34 for ; Wed, 23 Nov 2011 05:13:21 -0800 (PST) Received: by 10.204.154.1 with SMTP id m1mr24009362bkw.107.1322054001645; Wed, 23 Nov 2011 05:13:21 -0800 (PST) Received: from dvr.localnet (mail.360visiontechnology.com. [92.42.121.178]) by mx.google.com with ESMTPS id f14sm12840279bkv.3.2011.11.23.05.13.13 (version=TLSv1/SSLv3 cipher=OTHER); Wed, 23 Nov 2011 05:13:17 -0800 (PST) From: Andy Parkins To: bitcoin-development@lists.sourceforge.net Date: Wed, 23 Nov 2011 13:13:12 +0000 User-Agent: KMail/1.13.6 (Linux/3.0.0-1-686-pae; KDE/4.6.3; i686; ; ) References: <201111231035.48690.andyparkins@gmail.com> In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart1771003.jepphUgMgD"; protocol="application/pgp-signature"; micalg=pgp-sha1 Content-Transfer-Encoding: 7bit Message-Id: <201111231313.12534.andyparkins@gmail.com> 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 (andyparkins[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 0.0 AWL AWL: From: address is in the auto white-list X-Headers-End: 1RTCdk-0003X7-0F Subject: Re: [Bitcoin-development] Addressing rapid changes in mining power 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: Wed, 23 Nov 2011 13:13:31 -0000 --nextPart1771003.jepphUgMgD Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: quoted-printable On 2011 November 23 Wednesday, Christian Decker wrote: > The current block generation with a fixed difficulty was chosen because it > it clear when to adjust and to what target difficulty it has to be > adjusted. If we were to use synchronized time windows and select the > hardest block it gets incredibly complicated as synchronization is not > possible in distributed systems. Even the smallest drift would allow for > forks in the chain all over the place. Furthermore the delay in propagati= on > will also cause forks. >=20 > If 1/2 of the network see one block as the hardest, and for the rest of t= he > network it came too late then we'll have a fork that stays with us quite a > while. >=20 > The block chain is described as a timestamp server in the paper, but it is > more of a proof-of-existence before, as the contained timestamp cannot be > trusted anyway. These are reasonable objections. My counter is this: Let's view block difficulty as a measure of time, not time itself. The=20 timestamp is merely a convenience for the block. You cannot fake the=20 computing power needed for a particular difficulty; so the hardest chain=20 always wins (note: hardest chain). If I am a miner, I have two choices: (a) try to replace the top block on the current hardest chain (b) try to append to the current hardest chain Either of these is acceptable; but in case (a) I have to generate a more=20 difficult block to replace it; in case (b), at the start of the window, any= =20 difficulty is acceptable (however, I'm competing with other miners, so _any= _=20 difficulty won't beat them). The rule then is that you're trying to win the one block reward that is=20 available every 10 minutes; and your peers will be rejecting blocks with=20 timestamps that are lies. Perhaps an example... - I (a node), download the blockchain - The blockchain has N potential heads. Each of those heads has a time, t and a sum_of_difficulty. - The next block reward is going to go to the highest difficulty with t < timestamp < (t + T) _and_ verified timestamp (i.e. not received more than, say 5 minutes, from its claimed timestamp). - I can choose any head to start generating from, but given that it's the highest difficulty chain that's going to win the next reward (not the=20 highest difficulty block), I will surely pick the most difficult? - A rogue miner then issues a block with a fake timestamp; it actually generated at (t + T + 5) but claims (t + 5). Should I start using that block as my new head? Obviously not, because my peers might decide that it is a lie and reject it because it was received too late, making = my work useless. It is in my interest to pick a head that is honest. Resolving forks is easy: - 50 coins every ten minutes only - most difficult chain wins I'm certainly not saying it's a simple change. There are certainly areas I= =20 haven't thought about, and could be game-overs; but I do like the idea of=20 there being no target difficulty, and instead the blocks are issued at a fi= xed=20 ten minute rate (or rather the rewards are). Andy =2D-=20 Dr Andy Parkins andyparkins@gmail.com --nextPart1771003.jepphUgMgD Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iEYEABECAAYFAk7M8WgACgkQwQJ9gE9xL23jUwCeMGn+f43h9T9S9D8eWD1GpgUL WacAniocPuMKKHd/dH3stLrPyQK5Sc41 =Th78 -----END PGP SIGNATURE----- --nextPart1771003.jepphUgMgD--