From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 00FC812B9 for ; Sun, 27 Sep 2015 19:50:23 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ig0-f181.google.com (mail-ig0-f181.google.com [209.85.213.181]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 589E2EE for ; Sun, 27 Sep 2015 19:50:23 +0000 (UTC) Received: by igxx6 with SMTP id x6so38008603igx.1 for ; Sun, 27 Sep 2015 12:50:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=fDh7064dOUCg8owL0DDKOf7YkS13rLLx5GyBrj4Ktmc=; b=dX5aDvFB8SWJcob38mJogQ0zVFCaZ5ZCIrxFHp2+IsPmN0DCWWVFUpOEj8GL442ybZ 6wEEOnhqNr41xp6ykbSzav87zGbDEu3u7HcTSlp8xFhIkQRWsr06k8J/8TJdz9iF2rL9 He5cGlAkeq180Bv9gf2nOxio0e2LYLp8cU+VJMRnBgBKvHSCpM4QcI9lWhUo5D4A3EMt MOZHSTwBIqLN3wcINx6pOFJxCzrkLpBW5ZrowUMN3DPN97rfg+7ta2YZLQoMAXYw/OO+ YFPnn3i/1A6X10Lk9jX0EQBBx1/bBztZulq2tuZVsSEM8TGdevXBQ0Opo8yxni1JtY7m /PhQ== MIME-Version: 1.0 X-Received: by 10.50.27.5 with SMTP id p5mr12701188igg.66.1443383422736; Sun, 27 Sep 2015 12:50:22 -0700 (PDT) Received: by 10.107.19.30 with HTTP; Sun, 27 Sep 2015 12:50:22 -0700 (PDT) In-Reply-To: References: Date: Sun, 27 Sep 2015 19:50:22 +0000 Message-ID: From: Gregory Maxwell To: Kalle Rosenbaum Content-Type: text/plain; charset=UTF-8 X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Bitcoin Dev Subject: Re: [bitcoin-dev] Weak block thoughts... X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 27 Sep 2015 19:50:24 -0000 On Sun, Sep 27, 2015 at 3:10 PM, Kalle Rosenbaum via bitcoin-dev wrote: > I was mansplaining weak blocks to my wife. She asked a simple question: > > Why would I, as a miner, publish a weak block if I find one? > > I don't know. > Sure, I will get faster propagation for my solved block, should I find one. > On the other hand everybody else mining a similar block will enjoy the same > benefit. Assuming that I'm not a huge miner, it's unlikely that I will > actually solve the block, so I'm probably just giving away fast propagation > times to someone else. > So how does publishing a weak block benefit the producer of it more than the > other miners? Please help me understand this. Keep in mind, because of efficient differential transmission the cost to you is effectively nothing if your transaction acceptance policy is predictable, it's a hand-full of bytes sent. And by failing to send yours you do little to nothing to deny others the improvement. Lets imagine an alternative weak-blockless weak block implementation: Every N seconds, every miner send to every other miner what they're working on. This isn't totally crazy-- efficient differential transmission will keep the amount transmitted small. Any block found can be referenced to any of these earlier worklists. What the effect be of not transmitting yours? If your block is unlike everyone elses, you would suffer great delays in the event you found a block. If your block is mostly like everyone elses, you wouldn't suffer as much delay-- but the transmission costs would be negligible in that case. ... the size sent is proportional to the improvement you get when finding a block. In either case, no one else is harmed by you not sending yours... they still send their lists. A problem with that scheme is that unless you've layered an identity based access control system on it anyone can DOS attack it, because anyone can send as much as they want, they don't even have to be actual miners. What weak blocks adds to that is using hashcash as a rate limiting mechanism-- a coordination free lottery weighed by hash-power decides who can transmit. What if you don't participate in the lottery and share your solutions? No major harm for the other users... the other users will just choose a somewhat lower weak-block threshold to get the updates at the desired rate than they would otherwise. To the extent that what you were working on was different from anyone else, you'll suffer because you failed to make use of your chance to influence what could be efficiently transmitted to include your own blocks. You could also ask a question of why would you transitively relay someone elses announcement-- well if it helped their blocks too (by reflecting things they also want to mine) the answer is obvious. But what if it was disjoint from the things they wanted to mine and didn't help compared to the weak blocks they already relayed? In that case it's still in likely in their interest to relay it because if a block similar to it is produced and they extend that block they may end up orphaned because of propagation delays their parent block suffered. What if they receive an announcement which is so "ugly" that they wouldn't extend the chain with the strong block version of it (they'd intentionally try to fork it off?)-- in that case they wouldn't want to relay it. So much the same logic as why you relay other parties blocks applies, including-- relaying helps the network, but if you don't it'll still get along fine without you.