GnuPG

gpg is a complete and free implementation of the OpenPGP standard.

Export public key

To file

gpg --export name@example.net > my_key.pub

Send to server

gpg --export name@example.net | curl -T - https://keys.openpgp.org

Subkeys

It's possible to have multiple keys in one key.

Adding a subkey

gpg --edit-key <fingerprint>

gpg> addkey
# Follow the instructions