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 E7995D8B for ; Fri, 1 Jun 2018 01:20:50 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from ozlabs.org (ozlabs.org [203.11.71.1]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 288866B7 for ; Fri, 1 Jun 2018 01:20:50 +0000 (UTC) Received: by ozlabs.org (Postfix, from userid 1011) id 40xmjr0YPMz9ryk; Fri, 1 Jun 2018 11:20:47 +1000 (AEST) From: Rusty Russell To: Peter Todd , Bitcoin Protocol Discussion , "Christian Decker" In-Reply-To: <87muwhvozr.fsf@rustcorp.com.au> References: <87po25lmzs.fsf@rustcorp.com.au> <201805100227.42217.luke@dashjr.org> <87vabnq9ui.fsf@rustcorp.com.au> <87zi0tisft.fsf@rustcorp.com.au> <20180521035658.vfo4wx6ifum2s2o5@petertodd.org> <87muwhvozr.fsf@rustcorp.com.au> Date: Thu, 31 May 2018 12:17:58 +0930 Message-ID: <87h8mov8v5.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-0.9 required=5.0 tests=BAYES_00,DATE_IN_PAST_12_24 autolearn=no version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Matt Corallo Subject: Re: [bitcoin-dev] Making OP_TRUE standard? X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 Jun 2018 01:20:51 -0000 Rusty Russell writes: > AFAICT the optimal DoS is where: > > 1. Attacker sends a 100,000 vbyte tx @1sat/vbyte. > 2. Replaces it with a 108 vbyte tx @2sat/vbyte which spends one of > those inputs. > 3. Replaces that spent input in the 100k tx and does it again. > > It takes 3.5 seconds to propagate to 50% of network[1] (probably much worse > given 100k txs), so they can only do this about 86 times per block. > > That means they send 86 * (100000 + 108) = 8609288 vbytes for a cost of > 86 * 2 * 108 + 100000 / 2 = 68576 satoshi (assuming 50% chance 100k tx > gets mined). This 50% chance assumption is wrong; it's almost 0% for a low enough fee. Thus the cost is only 18576, making the cost for the transactions 463x lower than just sending 1sat/vbyte txs under optimal conditions. That's a bit ouch.[1] I think a better solution is to address the DoS potential directly: if a replacement doesn't meet #3 or #4, but *does* increase the feerate by at least minrelayfee, processing should be delayed by 30-60 seconds. That means that eventually you will RBF a larger tx, but it'll take much longer. Should be easy to implement, too, since similar timers will be needed for dandelion. Cheers, Rusty. [1] Christian grabbed some more detailed propagation stats for me: larger txs do propagate slower, but only by a factor of 2.5 or so.