From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1UcoCM-0005V4-0S for bitcoin-development@lists.sourceforge.net; Thu, 16 May 2013 02:45:42 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.215.45 as permitted sender) client-ip=209.85.215.45; envelope-from=gmaxwell@gmail.com; helo=mail-la0-f45.google.com; Received: from mail-la0-f45.google.com ([209.85.215.45]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UcoCK-0002xS-Tw for bitcoin-development@lists.sourceforge.net; Thu, 16 May 2013 02:45:41 +0000 Received: by mail-la0-f45.google.com with SMTP id ec20so2192497lab.18 for ; Wed, 15 May 2013 19:45:34 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.152.26.225 with SMTP id o1mr19444566lag.43.1368672334135; Wed, 15 May 2013 19:45:34 -0700 (PDT) Received: by 10.112.71.97 with HTTP; Wed, 15 May 2013 19:45:34 -0700 (PDT) In-Reply-To: References: <20130514115151.GA21600@netbook.cypherspace.org> <20130514140902.GA22447@netbook.cypherspace.org> <20130515102509.GA3401@netbook.cypherspace.org> <20130515111906.GA26020@savin> <20130515114956.GA5863@netbook.cypherspace.org> <5193825B.20909@lavabit.com> <20130515162129.GB6156@netbook.cypherspace.org> <20130515234030.GA17920@netbook.cypherspace.org> Date: Wed, 15 May 2013 19:45:34 -0700 Message-ID: From: Gregory Maxwell To: Mike Hearn Content-Type: text/plain; charset=UTF-8 X-Spam-Score: -1.6 (-) 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 (gmaxwell[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record -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: 1UcoCK-0002xS-Tw Cc: "bitcoin-development@lists.sourceforge.net" Subject: Re: [Bitcoin-development] blind symmetric commitment for stronger byzantine voting resilience (Re: bitcoin taint & unilateral revocability) 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, 16 May 2013 02:45:42 -0000 On Wed, May 15, 2013 at 7:22 PM, Mike Hearn wrote: > Conceptually it sounds a lot like ZeroCoin (not in implementation)? Zerocoin conceals the connection from everyone forever, assuming the underlying trapdoor problem is computational infeasible, but at great cost. Adamcoin, depending on how its done, at most conceals the transactions from people who aren't a party to them... though as time goes on eventually everyone becomes a party to a sufficiently old coin, and avoiding publication creates quadratic costs in evaluating a private clique's claims.... so instead an implementation would make the identities public but only once they're burred a bit. Perhaps an extreme version of the idea is easier to understand. Ignore DOS attacks for a moment and pretend there is never any address reuse: Everyone creates txouts paying a P2SH addresses that have a OP_PUSH nonce in them and tell you recipient the nonce out of band. When the recipients spend those coins they provide the script but not the nonce. The recipient knows what coins he's spending, but the public does not. The public can tell there is no double spend though, because they'd see the same script twice. The person he's paying may be skeptical that he actually has any coin and didn't just mine some gibberish, but our spender tells that their receiver the nonce, and that person can see the coin available for spending in the chain and also see that there are no double spends. This could actually go on forever with no ambiguity over who owns what, but the out of band proofs that you have to give people when you spend coins would grow with the history of the coins. Since there wouldn't be much privacy once a transaction was sufficiently split up in any case, you instead just publish the unblindings once transactions are sufficiently buried. Thus bounding the growth of the proofs. The reason I say I need to internalize this more is mostly that I need to think about attacks on the publication for 'tained' transactions being more or less isomorphic to just refusing to allow spending of the 'tainted' coins in any case.