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 1WTuFH-0003tY-Gz for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 14:28:27 +0000 Received-SPF: pass (sog-mx-4.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.160.179 as permitted sender) client-ip=209.85.160.179; envelope-from=watsonbladd@gmail.com; helo=mail-yk0-f179.google.com; Received: from mail-yk0-f179.google.com ([209.85.160.179]) by sog-mx-4.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1WTuFG-00081E-Ly for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 14:28:27 +0000 Received: by mail-yk0-f179.google.com with SMTP id 9so1772880ykp.10 for ; Sat, 29 Mar 2014 07:28:21 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.236.139.70 with SMTP id b46mr21093079yhj.63.1396103301001; Sat, 29 Mar 2014 07:28:21 -0700 (PDT) Sender: watsonbladd@gmail.com Received: by 10.170.63.197 with HTTP; Sat, 29 Mar 2014 07:28:20 -0700 (PDT) In-Reply-To: <1894130.91FUH3Vu6n@crushinator> References: <1878927.J1e3zZmtIP@crushinator> <1894130.91FUH3Vu6n@crushinator> Date: Sat, 29 Mar 2014 10:28:20 -0400 X-Google-Sender-Auth: 4nlfk1XxG7NpbPdareU3OFxm1kw Message-ID: From: Watson Ladd To: Matt Whitlock Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 (watsonbladd[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 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: 1WTuFG-00081E-Ly Cc: Bitcoin Dev Subject: Re: [Bitcoin-development] Presenting a BIP for Shamir's Secret Sharing of Bitcoin private keys 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: Sat, 29 Mar 2014 14:28:27 -0000 On Sat, Mar 29, 2014 at 10:10 AM, Matt Whitlock wro= te: > On Saturday, 29 March 2014, at 2:36 pm, Mike Hearn wrote: >> Right - the explanation in the BIP about the board of directors is IMO = a >> little misleading. The problem is with splitting a private key is that a= t >> some point, *someone* has to get the full private key back and they can >> then just remember the private key to undo the system. CHECKMULTISIG avo= ids >> this. > > The implication is that every director would want to retain the board's p= rivate key for himself but also would want to prevent every other director = from successfully retaining the private key for himself, leading to a perpe= tual stalemate in which no director ever gets to retain the private key. This is not the case: one can use MPC techniques to compute a signature from shares without reconstructing the private key. There is a paper on this for bitcoin, but I don't know where it is. > >> I can imagine that there may be occasional uses for splitting a wallet s= eed >> like this, like for higher security cold wallets, but I suspect an ongoi= ng >> shared account like a corporate account is still best off using >> CHECKMULTISIG or the n-of-m ECDSA threshold scheme proposed by Ali et al= . > > Multisig does not allow for the topology I described. Say the board has s= even directors, meaning the majority threshold is four. This means the orga= nization needs the consent of six individuals in order to sign a transactio= n: the president, the CFO, and any four of the board members. A 6-of-9 mult= isig would not accomplish the same policy, as then any six board members co= uld successfully sign a transaction without the consent of the president or= CFO. Of course the multi-signature scheme could be expanded to allow for h= ierarchical threshold topologies, or Shamir's Secret Sharing can be used to= distribute keys at the second level (and further, if desired). > > -------------------------------------------------------------------------= ----- > _______________________________________________ > Bitcoin-development mailing list > Bitcoin-development@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/bitcoin-development --=20 "Those who would give up Essential Liberty to purchase a little Temporary Safety deserve neither Liberty nor Safety." -- Benjamin Franklin