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Date: Sat, 08 Mar 2014 12:37:30 +0200
From: Joel Kaartinen <joel.kaartinen@gmail.com>
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Subject: Re: [Bitcoin-development] Is this a safe thing to be doing with ECC
 addition? (Oracle protocol)
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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
> <mailto: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
> http://www.socialminds.jp
>
> Reality Keys
> @realitykeys
> ed@realitykeys.com <mailto: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
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    <div class="moz-cite-prefix">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.<br>
      <br>
      Although, I have to wonder, why not just use multisig?<br>
      <br>
      - Joel<br>
      <br>
      On 08.03.2014 10:51, Edmund Edgar wrote:<br>
    </div>
    <blockquote
cite="mid:CA+su7OWx9jrgUJrOH=tg1968vr1G1w7yXjgaRSyYJ0zRBjwpqg@mail.gmail.com"
      type="cite">
      <div dir="ltr">
        <div class="gmail_extra">
          <div class="gmail_quote">On 8 March 2014 17:10, Alan Reiner <span
              dir="ltr">&lt;<a moz-do-not-send="true"
                href="mailto:etotheipi@gmail.com" target="_blank">etotheipi@gmail.com</a>&gt;</span>
            wrote:<br>
            <div>
              &nbsp;</div>
            <blockquote class="gmail_quote" style="margin:0 0 0
              .8ex;border-left:1px #ccc solid;padding-left:1ex">
              <div bgcolor="#FFFFFF" text="#000000"> I create a new
                keypair, &lt;c_pub&gt; with &lt;c_priv&gt; which I know
                (it can be any arbitrary key pair).&nbsp; But I don't give
                you &lt;c_pub&gt;, I give you&nbsp; &lt;b_pub&gt; =
                &lt;c_pub&gt; minus &lt;a_pub&gt; (which I can do
                because I've seen &lt;a_pub&gt; before doing this).&nbsp; <br>
                <br>
                Sure, I don't know the private key for &lt;b_pub&gt;,
                but it doesn't matter... because what <br>
                <br>
                &lt;b_pub&gt; + &lt;a_pub&gt; = &lt;c_pub&gt; (mine)<br>
                <br>
                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)</div>
            </blockquote>
            <div><br>
            </div>
            <div>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.&nbsp;</div>
          </div>
          <div><br>
          </div>
          -- <br>
          <div dir="ltr">
            <div>--&nbsp;</div>
            <div>Edmund Edgar</div>
            <div>Founder, Social Minds Inc (KK)</div>
            <div>Twitter: @edmundedgar</div>
            <div>Linked In: edmundedgar</div>
            <div>Skype: edmundedgar</div>
            <div><a moz-do-not-send="true"
                href="http://www.socialminds.jp" target="_blank">http://www.socialminds.jp</a></div>
            <div><br>
            </div>
            <div>Reality Keys</div>
            <div>@realitykeys</div>
            <div><a moz-do-not-send="true"
                href="mailto:ed@realitykeys.com" target="_blank">ed@realitykeys.com</a></div>
            <div><a moz-do-not-send="true"
                href="https://www.realitykeys.com" target="_blank">https://www.realitykeys.com</a></div>
          </div>
        </div>
      </div>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <pre wrap="">------------------------------------------------------------------------------
Subversion Kills Productivity. Get off Subversion &amp; 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.
<a class="moz-txt-link-freetext" href="http://pubads.g.doubleclick.net/gampad/clk?id=122218951&amp;iu=/4140/ostg.clktrk">http://pubads.g.doubleclick.net/gampad/clk?id=122218951&amp;iu=/4140/ostg.clktrk</a></pre>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <pre wrap="">_______________________________________________
Bitcoin-development mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Bitcoin-development@lists.sourceforge.net">Bitcoin-development@lists.sourceforge.net</a>
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</pre>
    </blockquote>
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