So when I tell synaptic package manager to reload, to get current information, I see "failed" for two of the things that it's trying to download. Then I get a box with error messages in it as follows:
"GPG error: https://download.virtualbox.org/virtualbox/debian stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A2F683C52980AECFThe repository 'https://download.virtualbox.org/virtualbox/debian stretch InRelease' is not signed."
I seem to vaguely recall something about a key on the Oracle site where I downloaded this, but am not 100% sure. What do I need to do to fix this?