From: Nokan Emiro <uzleepito@...>
Date: 2012-10-28T05:59:21+09:00
Subject: Re: OpenSSL ECDSA public key from private

--f46d04448141ca1f3904cd10b5f4
Content-Type: text/plain; charset=UTF-8

Much better, but it's still not finished...  ;-)

I had a look at the ruby code. #generate_key just calls openssl
> function "EC_KEY_generate_key". From  openssl.sourcearchive.com, I see
> that, within that function, the public key is generated with
>
>       if (eckey->pub_key == NULL)
>             {
>             pub_key = EC_POINT_new(eckey->group);
>             if (pub_key == NULL)
>                   goto err;
>             }
>
>
Thanks for looking at the source.  I guess this is just the creation
(memory allocation?) of the point object (yes, the public key is a
point with X and Y coordinates in Elliptic Curve crypto), but the
calculation of this point using the private key (which is a number,
not a point) must be somewhere in the next few lines in the source.


> EC_POINT_new is used within Ruby when creating an
> OpenSSL::PKey::EC::Point object, when passing it a 'group'. Now, I
> have no idea what a group is, but your key has a 'group'. And it is
> populated, even without calling #generate_key.
>
> If I run
>
> pub_key=OpenSSL::PKey::EC::Point.new(key.group)
>
> I get something. Again, I hope this is what you are looking for.
>

As far as I can see this creates a point with (0, 0) coordinates.
(The .to_bn converts a point to an OpenSSL::BN, which is a
Big Number, where (I think) the first N bit belongs to the X
coordinate and the other bits to the Y, but to_bn answers 0.)

According to this...

http://stackoverflow.com/questions/12480776/how-do-i-obtain-the-public-key-from-an-ecdsa-private-key-in-openssl

...I think EC_POINT_mul() could be a solution.  It's a C function
in OpenSSL, and it does the calculation I need.  But I don't know
much about how Ruby and C are married in native gems, and
I think the Ruby API does not allow me to call this C function. :(

Or does it?

The API should support private-to-public key calculations, however...

--f46d04448141ca1f3904cd10b5f4
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

Much better, but it&#39;s still not finished... =C2=A0;-)<br><br><div class=
=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex">
I had a look at the ruby code. #generate_key just calls openssl<br>
function &quot;EC_KEY_generate_key&quot;. From =C2=A0<a href=3D"http://open=
ssl.sourcearchive.com" target=3D"_blank">openssl.sourcearchive.com</a>, I s=
ee<br>
that, within that function, the public key is generated with<br>
<br>
=C2=A0 =C2=A0 =C2=A0 if (eckey-&gt;pub_key =3D=3D NULL)<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 {<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 pub_key =3D EC_POINT_new(eckey-&g=
t;group);<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (pub_key =3D=3D NULL)<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 goto err;<br=
>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }<br>
<br></blockquote><div><br></div><div>Thanks for looking at the source. =C2=
=A0I guess this is just the creation</div><div>(memory allocation?) of the =
point object (yes, the public key is a</div><div>point with X and Y coordin=
ates in Elliptic Curve crypto), but the</div>
<div>calculation of this point using the private key (which is a number,</d=
iv><div>not a point) must be somewhere in the next few lines in the source.=
</div><div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 =
0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">

EC_POINT_new is used within Ruby when creating an<br>
OpenSSL::PKey::EC::Point object, when passing it a &#39;group&#39;. Now, I<=
br>
have no idea what a group is, but your key has a &#39;group&#39;. And it is=
<br>
populated, even without calling #generate_key.<br>
<br>
If I run<br>
<br>
pub_key=3DOpenSSL::PKey::EC::Point.new(key.group)<br>
<br>
I get something. Again, I hope this is what you are looking for.<br></block=
quote><div><br></div><div>As far as I can see this creates a point with (0,=
 0) coordinates.</div><div>(The .to_bn converts a point to an OpenSSL::BN, =
which is a</div>
<div>Big Number, where (I think) the first N bit belongs to the X</div><div=
>coordinate=C2=A0and the other bits to the Y, but to_bn answers 0.)</div><d=
iv><br></div><div>According to this...</div><div><br></div><div><a href=3D"=
http://stackoverflow.com/questions/12480776/how-do-i-obtain-the-public-key-=
from-an-ecdsa-private-key-in-openssl">http://stackoverflow.com/questions/12=
480776/how-do-i-obtain-the-public-key-from-an-ecdsa-private-key-in-openssl<=
/a></div>
<div><br></div><div>...I think EC_POINT_mul() could be a solution. =C2=A0It=
&#39;s a C function</div><div>in OpenSSL, and it does the calculation I nee=
d. =C2=A0But I don&#39;t know</div><div>much about how Ruby and C are marri=
ed in native gems, and</div>
<div>I think the Ruby API does not allow me to call this C function. :(</di=
v><div><br></div><div>Or does it?</div><div><br></div><div>The API should s=
upport private-to-public key calculations, however...</div><div><br></div>
<div><br></div></div>

--f46d04448141ca1f3904cd10b5f4--