My public key is a GnuPG key that is kept on my desktop at home. If you send me a message encrypted with this key, then I cannot read it until I return home. But it has a realatively high level of security.
If you want to give me an account on a computer, feel free to use my SSH public key.
You can use Off-the-Record messaging with me. When you receive my key you can verify the fingerprints.
Some of my private keys have been published.