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[92.251.83.90]) by mx.google.com with ESMTPSA id k7sm13817798eeg.13.1969.12.31.16.00.00 (version=TLSv1.1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 01 Oct 2013 07:26:05 -0700 (PDT) Received: by netbook (Postfix, from userid 1000) id 5FD952E0B63; Tue, 1 Oct 2013 16:26:04 +0200 (CEST) Received: by flare (hashcash-sendmail, from uid 1000); Tue, 1 Oct 2013 16:26:03 +0200 Date: Tue, 1 Oct 2013 16:26:03 +0200 From: Adam Back To: Mark Friedenbach Message-ID: <20131001142603.GA9208@netbook.cypherspace.org> References: <2c70dbfc173749cf4198c591f19a7d33@astutium.com> <20130929093708.GA16561@netbook.cypherspace.org> <5248680C.60404@monetize.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <5248680C.60404@monetize.io> User-Agent: Mutt/1.5.21 (2010-09-15) X-Hashcash: 1:20:131001:mark@monetize.io::8QhV/lfngts6G955:00ErJ X-Hashcash: 1:20:131001:bitcoin-development@lists.sourceforge.net::ZHe+NbfGJzbch LfY:000000000000000000003MGc X-Hashcash: 1:20:131001:adam@cypherspace.org::4JXLdQjBkWNFQoNv:00000000000000000 00000000000000000000000018jr X-Spam-Score: -1.5 (-) 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 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (adam.back[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [URIs: bitcointalk.org] X-Headers-End: 1VR0tw-00044e-QL Cc: Bitcoin Dev Subject: [Bitcoin-development] homomorphic coin value (validatable but encrypted) (Re: smart contracts -- possible use case? yes or no?) 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: Tue, 01 Oct 2013 14:26:16 -0000 On Sun, Sep 29, 2013 at 10:49:00AM -0700, Mark Friedenbach wrote: >This kind of thing - providing external audits of customer accounts >without revealing private data - would be generally useful beyond >taxation. If you have any solutions, I'd be interested to hear them >(although bitcoin-dev is probably not the right place yet). Thanks for providing the impetus to write down the current state, the efficient version of which I only figured out a few days ago :) I have been researching this for a few months on and off, because it seems like an interesting construct in its own right, a different aspect of payment privacy (eg for auditable but commercial sensistive information) but also that other than its direct use it may enable some features that we have not thought of yet. I moved it to bitcointalk: https://bitcointalk.org/index.php?topic=305791.new#new Its efficient finally (after many dead ends): approximately 2x cost of current in terms of coin size and coin verification cost, however it also gives some perf advantages back in a different way - necessary changes to schnorr (EC version of Schnorr based proofs) allow n of n multiparty sigs, or k of n multiparty sigs for the verification cost and signature size of one pair of ECS signatures, for n > 2 its a space and efficiency improvement over current bitcoin. Adam