User authentication with key-file and gpg-agent

Hi!

Now that my initrd-script is ready and provides me with the means to
encrypt partitions with a gpg-encrypted key-file [1], I'd like to use
the very same file for user authentication.

It would be even better if gpg-agent could get it right from the user
authentication (pam) to use it for as many services as possible, ssh,
gpg, gnome-keyring (?), sudo (?), password database.

I think what I really want is something like a poor man's version of
smartcard authentication. 

Could you please give me some hints? I'd be pleased to hear any
comments, criticism and recommendations on that issue.

Thanks in advance!

Florian Philipp

[1] basically 1k of random data, encrypted with 3DES by gpg

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.7 (GNU/Linux)

iD8DBQBHzEkoqs4uOUlOuU8RAmAKAJ9ycpYr4qwLvkmWgreFBhEVvqXG9QCfeB7D
IqRf429ZKPKQYCscYd2GmF0=
=X1sa
-----END PGP SIGNATURE-----