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-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1W0mj6-0003fQ-8G for bitcoin-development@lists.sourceforge.net; Wed, 08 Jan 2014 06:34:52 +0000 Received-SPF: pass (sog-mx-2.v43.ch3.sourceforge.com: domain of taplink.co designates 50.117.27.232 as permitted sender) client-ip=50.117.27.232; envelope-from=jeremy@taplink.co; helo=mail.taplink.co; Received: from mail.taplink.co ([50.117.27.232]) by sog-mx-2.v43.ch3.sourceforge.com with smtp (Exim 4.76) id 1W0mj5-00055R-FM for bitcoin-development@lists.sourceforge.net; Wed, 08 Jan 2014 06:34:52 +0000 Received: from laptop-air.hsd1.ca.comcast.net ([192.168.168.135]) by mail.taplink.co ; Tue, 7 Jan 2014 22:41:23 -0800 Content-Type: text/plain; charset=iso-8859-15; format=flowed; delsp=yes To: bitcoin-development@lists.sourceforge.net, "Peter Todd" References: <20140106025312.GC2356@savin> Date: Tue, 07 Jan 2014 22:34:46 -0800 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: "Jeremy Spilman" Organization: TapLink Message-ID: In-Reply-To: <20140106025312.GC2356@savin> User-Agent: Opera Mail/1.0 (Win32) oclient: 192.168.168.135#jeremy@taplink.co#465 X-Spam-Score: -1.7 (-) 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 SPF_PASS SPF: sender matches SPF record -0.1 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -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 X-Headers-End: 1W0mj5-00055R-FM Subject: Re: [Bitcoin-development] Privacy and blockchain data 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, 08 Jan 2014 06:34:52 -0000 > > 2) Common prefixes: Generate addresses such that for a given wallet they > all share a fixed prefix. The length of that prefix determines the > anonymity set and associated privacy/bandwidth tradeoff, which > remainds a fixed ratio of all transactions for the life of the > wallet. > Interesting thought to make the privacy/bandwidth trade-off using vanitygen and prefix filters. But doesn't this effectively expand the universe of potential spies from 'the global attacker' who is watching your SPV queries, to simply 'the globe' -- anyone with a copy of the blockchain? Some stats on UTXO set size: (slightly stale -- as of block 270733) 7.4m unspent outputs 2.2m transactions with unspent outputs 2.1m unique unspent scriptPubKeys Side note: the top 1,000 scriptPubKeys have 10% of all unspent outputs. Let's say you use an 8-bit prefix (1/256) that would be ~10,000 transactions in the UTXO you would be monitoring. But if I knew a few different days / time-periods you transacted, I could figure out your prefix. Of course, anyone you transact with would know your prefix outright. Wouldn't this also allow obvious identification of spend versus change addresses in a transaction?