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-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1WTxYM-0006SJ-Jv for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 18:00:22 +0000 X-ACL-Warn: Received: from qmta09.westchester.pa.mail.comcast.net ([76.96.62.96]) by sog-mx-4.v43.ch3.sourceforge.com with esmtp (Exim 4.76) id 1WTxYL-00066n-LZ for bitcoin-development@lists.sourceforge.net; Sat, 29 Mar 2014 18:00:22 +0000 Received: from omta20.westchester.pa.mail.comcast.net ([76.96.62.71]) by qmta09.westchester.pa.mail.comcast.net with comcast id jVrh1n0071YDfWL59W0GrE; Sat, 29 Mar 2014 18:00:16 +0000 Received: from crushinator.localnet ([IPv6:2601:6:4800:47f:219:d1ff:fe75:dc2f]) by omta20.westchester.pa.mail.comcast.net with comcast id jW0F1n00W4VnV2P3gW0GML; Sat, 29 Mar 2014 18:00:16 +0000 From: Matt Whitlock To: Alan Reiner Date: Sat, 29 Mar 2014 14:00:15 -0400 Message-ID: <2135731.4HGHfZWzo5@crushinator> User-Agent: KMail/4.12.3 (Linux/3.12.13-gentoo; KDE/4.12.3; x86_64; ; ) In-Reply-To: <53370854.5050303@gmail.com> References: <15872432.k8h0hUxqlf@crushinator> <53370854.5050303@gmail.com> 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 [76.96.62.96 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: 1WTxYL-00066n-LZ Cc: bitcoin-development@lists.sourceforge.net 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 18:00:22 -0000 On Saturday, 29 March 2014, at 1:52 pm, Alan Reiner wrote: > On 03/29/2014 01:19 PM, Matt Whitlock wrote: > > I intentionally omitted the parameter M (minimum subset size) from the shares because including it would give an adversary a vital piece of information. Likewise, including any kind of information that would allow a determination of whether the secret has been correctly reconstituted would give an adversary too much information. Failing silently when given incorrect shares or an insufficient number of shares is intentional. > > I do not believe this is a good tradeoff. It's basically obfuscation of > something that is already considered secure at the expense of > usability. It's much more important to me that the user understands > what is in their hands (or their family members after they get hit by a > bus), than to obfuscate the parameters of the secret sharing to provide > a tiny disadvantage to an adversary who gets ahold of one. > > The fact that it fails silently is really all downside, not a benefit. > If I have enough fragments, I can reconstruct the seed and see that it > produces addresses with money. If not, I know I need more fragments. > I'm much more concerned about my family having all the info they need to > recover the money, than an attacker knowing that he needs two more > fragments instead of which are well-secured anyway. For what it's worth, ssss also omits from the shares any information about the threshold. It will happily return a garbage secret if too few shares are combined. (And actually, it will happily return a garbage secret if too *many* shares are combined, too. My implementation does not have that problem.)