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-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1WYKmH-00075t-Ae for bitcoin-development@lists.sourceforge.net; Thu, 10 Apr 2014 19:36:49 +0000 Received: from mail-pd0-f175.google.com ([209.85.192.175]) by sog-mx-3.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1WYKmG-000516-4X for bitcoin-development@lists.sourceforge.net; Thu, 10 Apr 2014 19:36:49 +0000 Received: by mail-pd0-f175.google.com with SMTP id x10so4277425pdj.20 for ; Thu, 10 Apr 2014 12:36:42 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:organization:user-agent :mime-version:to:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=ZVTsUkdeqD10ZHuJ26iavzF1qkprjGQmFtz3i+8RPVY=; b=Ywam8yOBcnyG6F90rI52H8mMMZcNFm9+mJXJj0WGMlc5i+5efj7/pXnD4mJGZixiHN S7US2NLSP+5U5D2wndPc7Egu3IvWiq1h1VZ8mLu6ERx6n/dynJKrahp5CfvozLytWobE HqPIX/3NN5ZLfRQp8kSyP0lrKRG0Dqx5IL8CsLz1SOB2OSDG17jbqJPzFqjM+FTCsspK VsHEgHQiRBvQSOpNFpdGaBpX61ei+dcsBW9BuVAnsfR0tOJpUhsW2Ly5id28YhF5pAAk yfg2cYRaYulV5CY1o3jkj3pm18hgMQ1kkkOPH79erbM8r1kD8c+cOPb7DK9Rj0iuAbKM 9ScQ== X-Gm-Message-State: ALoCoQmdUOI3vPeiD/x1FPaXOyxgV89egzCjdk+d/gmGaAIc4bBigmq0plK2Jr3R7C/SQotDyq7B X-Received: by 10.67.14.98 with SMTP id ff2mr21814871pad.101.1397158602137; Thu, 10 Apr 2014 12:36:42 -0700 (PDT) Received: from [192.168.127.226] (50-0-36-93.dsl.dynamic.sonic.net. [50.0.36.93]) by mx.google.com with ESMTPSA id om6sm10816796pbc.43.2014.04.10.12.36.40 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 10 Apr 2014 12:36:41 -0700 (PDT) Message-ID: <5346F2C7.1050809@monetize.io> Date: Thu, 10 Apr 2014 12:36:39 -0700 From: Mark Friedenbach Organization: Monetize.io Inc. User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: bitcoin-development@lists.sourceforge.net References: In-Reply-To: X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Spam-Score: 0.0 (/) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [209.85.192.175 listed in list.dnswl.org] X-Headers-End: 1WYKmG-000516-4X Subject: Re: [Bitcoin-development] Chain pruning 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: Thu, 10 Apr 2014 19:36:49 -0000 You took the quote out of context: "a full node can copy the chain state from someone else, and check that its hash matches what the block chain commits to. It's important to note that this is a strict reduction in security: we're now trusting that the longest chain (with most proof of work) commits to a valid UTXO set (at some point in the past)." The described synchronization mechanism would be to determine the most-work block header (SPV level of security!), and then sync the UTXO set committed to within that block. This is strictly less security than building the UTXO set yourself because it is susceptible to a 51% attack which violates protocol rules. On 04/10/2014 11:19 AM, Paul Rabahy wrote: > You say UTXO commitments is "a strict reduction in security". If UTXO > commitments were rolled in as a soft fork, I do not see any new attacks > that could happen to a person trusting the committed UTXO + any > remaining blocks to catch up to the head. > > I would imagine the soft fork to proceed similar to the following. > 1. Miners begin including UTXO commitments. > 2. Miners begin rejecting blocks with invalid UTXO commitments. > 3. Miners begin rejecting blocks with no UTXO commitments. > > To start up a fresh client it would follow the following. > 1. Sync headers. > 2. Pick a committed UTXO that is deep enough to not get orphaned. > 3. Sync blocks from commitment to head. > > I would argue that a client following this methodology is strictly more > secure than SPV, and I don't see any attacks that make it less secure > than a full client. It is obviously still susceptible to a 51% attack, > but so is the traditional block chain. I also do not see any sybil > attacks that are strengthened by this change because it is not modifying > the networking code. > > I guess if the soft fork happened, then miners began to not include the > UTXO commitment anymore, it would lower the overall network hash rate, > but this would be self-harming to the miners so they have an incentive > to not do it. > > Please let me know if I have missed something.