Based on your answer #2, I'm thinking that gpg might not be the tool to use so I'm looking into openssl which has a bazillion options as well.
RE #3 in your response, I'm certainly the admin of my workstation, but I will not always be admin. I need to work up a scheme that doesn't require any special privileges. Additionally, it introduces a sysadmin chore to add any necessary keys to a key ring -- I'm really hoping to rig up a PHP-only solution (which may end up calling some CLI commands but that's OK -- the fewer the better).
I've definitely gotten some good advice in the security forum -- and this is a security sort of question. Maybe I'll do that in a bit here if I can't make any progress.
I think the first thing I need to figure out is what the heck is my public key's format
. Sadly, I don't know much about key pair formats and I'm not sure if my file is DER, PEM, x509 or what. I don't think it's x509, but I know very little about the various key formats (or where there are so damn many).
It looks something like this:
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v2.0.17 (MingW32)
-----END PGP PUBLIC KEY BLOCK-----