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 1RTEqS-0000K3-Uy for bitcoin-development@lists.sourceforge.net; Wed, 23 Nov 2011 15:34:44 +0000 Received-SPF: pass (sog-mx-2.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.212.47 as permitted sender) client-ip=209.85.212.47; envelope-from=etotheipi@gmail.com; helo=mail-vw0-f47.google.com; Received: from mail-vw0-f47.google.com ([209.85.212.47]) by sog-mx-2.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1RTEqO-0007LR-W9 for bitcoin-development@lists.sourceforge.net; Wed, 23 Nov 2011 15:34:44 +0000 Received: by vbbfc21 with SMTP id fc21so258282vbb.34 for ; Wed, 23 Nov 2011 07:34:35 -0800 (PST) Received: by 10.52.36.41 with SMTP id n9mr26008791vdj.41.1322062475525; Wed, 23 Nov 2011 07:34:35 -0800 (PST) Received: from [192.168.1.85] (c-76-111-108-35.hsd1.md.comcast.net. [76.111.108.35]) by mx.google.com with ESMTPS id a2sm18787231vdj.3.2011.11.23.07.34.34 (version=SSLv3 cipher=OTHER); Wed, 23 Nov 2011 07:34:34 -0800 (PST) Message-ID: <4ECD12AA.6080605@gmail.com> Date: Wed, 23 Nov 2011 10:35:06 -0500 From: Alan Reiner User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20110921 Thunderbird/3.1.15 MIME-Version: 1.0 To: bitcoin-development@lists.sourceforge.net References: <201111231035.48690.andyparkins@gmail.com> <201111231313.12534.andyparkins@gmail.com> In-Reply-To: Content-Type: multipart/alternative; boundary="------------020304080106000507000405" X-Spam-Score: -0.8 (/) 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 (etotheipi[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 1.0 HTML_MESSAGE BODY: HTML included in message -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 -0.2 AWL AWL: From: address is in the auto white-list X-Headers-End: 1RTEqO-0007LR-W9 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 15:34:45 -0000 This is a multi-part message in MIME format. --------------020304080106000507000405 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit I can substantiate Gavin's point quite powerfully: a couple months ago I did a search for the "hardest" block in the network and found a *very **impressive* one: https://bitcointalk.org/index.php?topic=29675.0 That block has a difficulty of **36 billion** when the network had a difficulty of **1.5 million**, which is 24,000 times harder than the target. If we were going by the /actual /hardest chain instead target-based-hardest chain, /then this block produced in July would might still represent the longest chain!/ Yes, that means that whichever miner produced this block, could've held onto it for 2-4 months without doing anything else, and then broadcast it to fork the blockchain from a block produced months ago. That's not theoretical, that's real data in the blockchain and it would be a disaster. -Alan On 11/23/2011 10:09 AM, Gavin Andresen wrote: > On Wed, Nov 23, 2011 at 9:38 AM, Christian Decker > wrote: >> At some point you might find an incredibly hard block that makes your forked >> chain the hardest one in the network > Seems to me that's the real problem with any "hardest block found in X > minutes" scheme. > > If I get lucky and find a really extremely hard block then I have an > incentive to keep it secret and build a couple more blocks on top of > it, then announce them all at the same time. > > If the rest of the network rejects my longer chain because I didn't > announce the extremely hard block in a timely fashion... then how > could the network ever recover from a real network split? A network > split/rejoin will look exactly the same. > > Bitcoin as-is doesn't have the "I got lucky and found an extremely > hard block" problem because the difficulty TARGET is used to compute > chain difficulty, not the actual hashes found. > > > --- > > PS: I proposed a different method for dealing with large hash power > drops for the testnet on the Forums yesterday, and am testing it > today. > --------------020304080106000507000405 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit I can substantiate Gavin's point quite powerfully: a couple months ago I did a search for the "hardest" block in the network and found a very impressive one:

https://bitcointalk.org/index.php?topic=29675.0

That block has a difficulty of *36 billion* when the network had a difficulty of *1.5 million*, which is 24,000 times harder than the target.  If we were going by the actual hardest chain instead target-based-hardest chain, then this block produced in July would might still represent the longest chain!

Yes, that means that whichever miner produced this block, could've held onto it for 2-4 months without doing anything else, and then broadcast it to fork the blockchain from a block produced months ago.  That's not theoretical, that's real data in the blockchain and it would be a disaster.

-Alan



On 11/23/2011 10:09 AM, Gavin Andresen wrote: 
On Wed, Nov 23, 2011 at 9:38 AM, Christian Decker
<decker.christian@gmail.com> wrote:

At some point you might find an incredibly hard block that makes your forked
chain the hardest one in the network

Seems to me that's the real problem with any "hardest block found in X
minutes" scheme.

If I get lucky and find a really extremely hard block then I have an
incentive to keep it secret and build a couple more blocks on top of
it, then announce them all at the same time.

If the rest of the network rejects my longer chain because I didn't
announce the extremely hard block in a timely fashion... then how
could the network ever recover from a real network split?  A network
split/rejoin will look exactly the same.

Bitcoin as-is doesn't have the "I got lucky and found an extremely
hard block" problem because the difficulty TARGET is used to compute
chain difficulty, not the actual hashes found.


---

PS: I proposed a different method for dealing with large hash power
drops for the testnet on the Forums yesterday, and am testing it
today.

--------------020304080106000507000405--