Adding the secp256k1 curve for ECDSA

[NIIBE Yutaka]

Hello,

I added support of the secp256k1 curve in libgcrypt.  Next, I'd like
to add a feature of ECDSA with secp256k1 to GnuPG.

My plan is to enable gpg-agent sign transactions of Bitcoin, and to
extend Gnuk so that it can store Bitcoin's private key and can compute
ECDSA of the curve secp256k1.  I'm considering Electrum as Bitcoin
client.

In the lower layer, I'm considering using INTERNAL AUTHENTICATE
command in the OpenPGP card specification (like gpg-agent as ssh-agent
uses that command).

Any suggestions, comments are welcome.

Direct questions of mine were:

   Is there any good Bitcoin client?
   Where could I put my private key of Bitcoin?
--