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 1WTulc-0004y4-Ie for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 15:01:52 +0000 X-ACL-Warn: Received: from qmta12.westchester.pa.mail.comcast.net ([76.96.59.227]) by sog-mx-2.v43.ch3.sourceforge.com with esmtp (Exim 4.76) id 1WTulb-0001uZ-Ot for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 15:01:52 +0000 Received: from omta11.westchester.pa.mail.comcast.net ([76.96.62.36]) by qmta12.westchester.pa.mail.comcast.net with comcast id jRyC1n0080mv7h05CT1myc; Sat, 29 Mar 2014 15:01:46 +0000 Received: from crushinator.localnet ([IPv6:2601:6:4800:47f:219:d1ff:fe75:dc2f]) by omta11.westchester.pa.mail.comcast.net with comcast id jT1l1n01Q4VnV2P3XT1mfH; Sat, 29 Mar 2014 15:01:46 +0000 From: Matt Whitlock To: Gregory Maxwell Date: Sat, 29 Mar 2014 11:01:45 -0400 Message-ID: <2288723.8YLNJJXu0j@crushinator> User-Agent: KMail/4.12.3 (Linux/3.12.13-gentoo; KDE/4.12.3; x86_64; ; ) In-Reply-To: References: <1878927.J1e3zZmtIP@crushinator> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" 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 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [76.96.59.227 listed in list.dnswl.org] 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: 1WTulb-0001uZ-Ot 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 15:01:52 -0000 On Saturday, 29 March 2014, at 7:36 am, Gregory Maxwell wrote: > On Sat, Mar 29, 2014 at 7:28 AM, Watson Ladd wrote: > > 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. > > Practically speaking you cannot unless the technique used is one > carefully selected to make it possible. This proposal isn't such a > scheme I beleieve, however, and I think I'd strongly prefer that we > BIP standardize a formulation which also has this property. I too would prefer that, but I do not believe there exists a method for computing a traditional signature from decomposed private key shares. Unless I'm mistaken, the composed signature has a different formula and requires a different verification algorithm from the ECDSA signatures we're using today. Thus, such a scheme would require a change to the Bitcoin scripting language. I specifically did not want to address that in my BIP because changes like that take too long. I am aiming to be useful in the present.