I am working with Ubuntu 16.04.5 LTS.
If I run
sudo apt-get update in the terminal, I get:
W: GPG error: https://repo.pbis.beyondtrust.com/apt pbiso InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FDE053D27237D0AC W: The repository 'https://repo.pbis.beyondtrust.com/apt pbiso InRelease' is not signed. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details.
So I then try running
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys FDE053D27237D0AC, and the command just sits there for a few minutes until it fails with the message:
gpg: requesting key 7237D0AC from hkp server keyserver.ubuntu.com gpg: keyserver timed out gpg: keyserver receive failed: keyserver error
I have already gone into
/etc/apt/apt.conf and added the lines
Acquire::http::proxy "<my company's proxy>"; Acquire::https::proxy "<my company's proxy>";