From: Nokan Emiro <uzleepito@...>
Date: 2012-10-28T05:23:39+09:00
Subject: Re: OpenSSL ECDSA public key from private

--f46d043c7f422179f104cd1036b9
Content-Type: text/plain; charset=UTF-8

I haven't looked into how to do this in Ruby, but at least with the
> command-line stuff from OpenSSL it seems to be trivial.  (That's quite
> contrary to my initial assumptions.  I was all set to tell you "no,
> the whole point is that you can't derive one from the other", and was
> fact-checking.  Apparently asymmetrical crypto is even more
> asymmetrical than I thought!)  Check out the answers to this question
> on SO:
>
>
> http://stackoverflow.com/questions/696472/given-a-private-key-is-it-possible-to-derive-its-public-key
>

Well, this is about RSA, not Elliptic Curve crypto (ECDSA), but the
main thing is all the same:  it should be easy to calculate the public
key from the private key, but it must be virtually impossible to do it
the other way.  The private key is just a huge random number that is
kept secret, and the public key is calculated from it somehow -- we
actually don't need to know how, that's something OpenSSL does
internally.

I think the Ruby API just misses a very important piece here. :(

--f46d043c7f422179f104cd1036b9
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<br><br><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I haven&=
#39;t looked into how to do this in Ruby, but at least with the<br>
command-line stuff from OpenSSL it seems to be trivial. =C2=A0(That&#39;s q=
uite<br>
contrary to my initial assumptions. =C2=A0I was all set to tell you &quot;n=
o,<br>
the whole point is that you can&#39;t derive one from the other&quot;, and =
was<br>
fact-checking. =C2=A0Apparently asymmetrical crypto is even more<br>
asymmetrical than I thought!) =C2=A0Check out the answers to this question<=
br>
on SO:<br>
<br>
=C2=A0<a href=3D"http://stackoverflow.com/questions/696472/given-a-private-=
key-is-it-possible-to-derive-its-public-key" target=3D"_blank">http://stack=
overflow.com/questions/696472/given-a-private-key-is-it-possible-to-derive-=
its-public-key</a><span class=3D"HOEnZb"><font color=3D"#888888"><br>
</font></span></blockquote><div><br></div><div>Well, this is about RSA, not=
 Elliptic Curve crypto (ECDSA), but the</div><div>main thing is all the sam=
e: =C2=A0it should be easy to calculate the public</div><div>key from the p=
rivate key, but it must be virtually impossible to do it</div>
<div>the other way. =C2=A0The private key is just a huge random number that=
 is</div><div>kept secret, and the public key is calculated from it somehow=
 -- we</div><div>actually don&#39;t need to know how, that&#39;s something =
OpenSSL does</div>
<div>internally.</div><div><br></div><div>I think the Ruby API just misses =
a very important piece here. :(</div><div><br></div><div><br></div></div>

--f46d043c7f422179f104cd1036b9--