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[76.111.96.126]) by mx.google.com with ESMTPSA id s13sm43103505qag.19.2014.03.08.15.13.10 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 08 Mar 2014 15:13:11 -0800 (PST) Message-ID: <531BA406.4070900@gmail.com> Date: Sat, 08 Mar 2014 18:13:10 -0500 From: Alan Reiner User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: bitcoin-development@lists.sourceforge.net References: <531AD080.40501@gmail.com> <531AF2EA.50904@gmail.com> In-Reply-To: <531AF2EA.50904@gmail.com> X-Enigmail-Version: 1.6 Content-Type: multipart/alternative; boundary="------------000409020903010500080106" X-Spam-Score: -0.6 (/) 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 (etotheipi[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 1.0 HTML_MESSAGE BODY: HTML included in message -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: 1WMQQf-0001j0-75 Subject: Re: [Bitcoin-development] Is this a safe thing to be doing with ECC addition? (Oracle protocol) 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, 08 Mar 2014 23:13:19 -0000 This is a multi-part message in MIME format. --------------000409020903010500080106 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Note that one of the reasons why this is insecure is because EC point addition is invertible. EC-scalar multiplication is not, thus why EC Diffie-Hellman is secure even when this asymmetry exists. A good cryptosystem doesn't have strange restrictions, like "your public key can only be public sometimes, but needs to protected like your private key other times." If you have to worry about things like that, you're doing it wrong :) -Alan On 03/08/2014 05:37 AM, Joel Kaartinen wrote: > If both parties insist on seeing a hash of the other party's public > key before they'll show their own public key, they can be sure that > the public key is not chosen based on the public key they themselves > presented. > > Although, I have to wonder, why not just use multisig? > > - Joel > > On 08.03.2014 10:51, Edmund Edgar wrote: >> On 8 March 2014 17:10, Alan Reiner > > wrote: >> >> >> I create a new keypair, with which I know (it >> can be any arbitrary key pair). But I don't give you , I >> give you = minus (which I can do because >> I've seen before doing this). >> >> Sure, I don't know the private key for , but it doesn't >> matter... because what >> >> + = (mine) >> >> You have no way to detect this condition, because you don't know >> what c_pub/c_priv I created, so you can only detect this after >> it's too late (after I abuse the private key) >> >> >> Thanks Alan and Forrest, that makes sense. So to salvage the >> situation in the original case, we have to make sure the parties >> exchange their public keys first, before they're allowed to see the >> public keys they'll be combining them with. >> >> -- >> -- >> Edmund Edgar >> Founder, Social Minds Inc (KK) >> Twitter: @edmundedgar >> Linked In: edmundedgar >> Skype: edmundedgar >> http://www.socialminds.jp >> >> Reality Keys >> @realitykeys >> ed@realitykeys.com >> https://www.realitykeys.com >> >> >> ------------------------------------------------------------------------------ >> Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. >> With Perforce, you get hassle-free workflows. Merge that actually works. >> Faster operations. Version large binaries. Built-in WAN optimization and the >> freedom to use Git, Perforce or both. Make the move to Perforce. >> http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk >> >> >> _______________________________________________ >> Bitcoin-development mailing list >> Bitcoin-development@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/bitcoin-development > > > > ------------------------------------------------------------------------------ > Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. > With Perforce, you get hassle-free workflows. Merge that actually works. > Faster operations. Version large binaries. Built-in WAN optimization and the > freedom to use Git, Perforce or both. Make the move to Perforce. > http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk > > > _______________________________________________ > Bitcoin-development mailing list > Bitcoin-development@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/bitcoin-development --------------000409020903010500080106 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Note that one of the reasons why this is insecure is because EC point addition is invertible.  EC-scalar multiplication is not, thus why EC Diffie-Hellman is secure even when this asymmetry exists.

A good cryptosystem doesn't have strange restrictions, like "your public key can only be public sometimes, but needs to protected like your private key other times."  If you have to worry about things like that, you're doing it wrong :)

-Alan


On 03/08/2014 05:37 AM, Joel Kaartinen wrote:
If both parties insist on seeing a hash of the other party's public key before they'll show their own public key, they can be sure that the public key is not chosen based on the public key they themselves presented.

Although, I have to wonder, why not just use multisig?

- Joel

On 08.03.2014 10:51, Edmund Edgar wrote:
On 8 March 2014 17:10, Alan Reiner <etotheipi@gmail.com> wrote:
 
I create a new keypair, <c_pub> with <c_priv> which I know (it can be any arbitrary key pair).  But I don't give you <c_pub>, I give you  <b_pub> = <c_pub> minus <a_pub> (which I can do because I've seen <a_pub> before doing this). 

Sure, I don't know the private key for <b_pub>, but it doesn't matter... because what

<b_pub> + <a_pub> = <c_pub> (mine)

You have no way to detect this condition, because you don't know what c_pub/c_priv I created, so you can only detect this after it's too late (after I abuse the private key)

Thanks Alan and Forrest, that makes sense. So to salvage the situation in the original case, we have to make sure the parties exchange their public keys first, before they're allowed to see the public keys they'll be combining them with. 

--
-- 
Edmund Edgar
Founder, Social Minds Inc (KK)
Twitter: @edmundedgar
Linked In: edmundedgar
Skype: edmundedgar

Reality Keys
@realitykeys


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Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce.
With Perforce, you get hassle-free workflows. Merge that actually works. 
Faster operations. Version large binaries.  Built-in WAN optimization and the
freedom to use Git, Perforce or both. Make the move to Perforce.
http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk


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Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce.
With Perforce, you get hassle-free workflows. Merge that actually works. 
Faster operations. Version large binaries.  Built-in WAN optimization and the
freedom to use Git, Perforce or both. Make the move to Perforce.
http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk


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