From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-4.v43.ch3.sourceforge.com ([172.29.43.194] helo=mx.sourceforge.net) by sfs-ml-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1StDTl-0003Rl-O3 for bitcoin-development@lists.sourceforge.net; Mon, 23 Jul 2012 07:54:57 +0000 X-ACL-Warn: Received: from petersson.at ([213.239.210.117]) by sog-mx-4.v43.ch3.sourceforge.com with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76) id 1StDTk-0000sa-KM for bitcoin-development@lists.sourceforge.net; Mon, 23 Jul 2012 07:54:57 +0000 Received: by petersson.at (Postfix, from userid 65534) id 35F9519A002; Mon, 23 Jul 2012 09:54:50 +0200 (CEST) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on petersson.at X-Spam-Level: X-Spam-Status: No, score=-1.0 required=4.0 tests=ALL_TRUSTED autolearn=disabled version=3.3.1 Received: from [192.168.0.199] (chello084114039092.14.vie.surfer.at [84.114.39.92]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: andreas) by petersson.at (Postfix) with ESMTPSA id A74D419A001 for ; Mon, 23 Jul 2012 09:54:49 +0200 (CEST) Message-ID: <500D0348.4010604@petersson.at> Date: Mon, 23 Jul 2012 09:54:48 +0200 From: Andreas Petersson User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:14.0) Gecko/20120713 Thunderbird/14.0 MIME-Version: 1.0 To: bitcoin-development@lists.sourceforge.net References: <1339766346.31489.49.camel@bmthinkpad> <1339771184.31489.53.camel@bmthinkpad> <1340132998.6065.7.camel@bmthinkpad> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed 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 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay domain X-Headers-End: 1StDTk-0000sa-KM Subject: Re: [Bitcoin-development] New P2P commands for diagnostics, SPV clients 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: Mon, 23 Jul 2012 07:54:57 -0000 Some concerns regarding Bloom Filters. I talked with Stefan Thomas on the Hackathon Berlin about this. I tried to follow the discussion closely but i have not taken a look at the code yet (is there already an implementation?) so please correct me if i got something wrong. The way the Bloom filters are planned now this requires a complicated setup. basically the client will ask the server to replay the whole blockchain, but filtered. This is not optimal for the following reasons: This will require the server to do a full scan of his data and only filter out non-matching entries. Really lightweight clients (like Bitcoincard), clients with shared private keys (electrum-style), or brainwallets - will ask the following question quite often to "supernodes": Given my public keys/addresses, what is the list of unspent outputs. i think it would make sense to include such a command, instead or in addition to the filterload/filterinit. And perhaps more severe: as far as i understand classic bloom filters, the server has no method of indexing his data for the expected requests. There is simply no data structure (or maybe it has to be invented) which allows the use of an index for queries by bloom filters of *varying length* and a generic hashing method. im not sure what a really efficient data structure for these kinds of query is. but i think it should be possible to find a good compromise between query flexibility, server load, client privacy. one possible scheme, looks like this: the client takes his list of addesses he is interested in. he hashes all of them to a fixed-length bit array (bloom filter) of length 64KiB (for example), and combines them with | to add more 1's with each address. the server maintains a binary tree data structure of unspent outputs arranged by the Bloom filter bits. to build the tree, the server would need to calculate the 64KiB bits for each address and arrange them in a binary tree. that way he can easily traverse the tree for a given bloom query. if a client whishes to query more broadly he can calculate the bloom filter to 64KiB and after that fill up the last 50% of the Bits with 1. or 95%. the trailing 1 bits even don't need to be transmitted to the server when a client is querying. of course, if the client is more privacy-concerned he could also fill up random bits with 1, which would not change much actually. the value of 64KiB is just out of thin air. according to my experimentation using BloomFilter from Guava - currently, also 8KiB would be sufficient to hava a 3% false positive rate for the 40000 active addresses we have right now. someone more familiar with hashing should please give his opinion if cutting a bloom filter in half has any bad consequences. Andreas