When using apt-get update you might get an error similar to the following.

resolve GPG error: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA

To fix this you will need to download and add a key.

You will need to get the key by running the following command.

apt-key adv --keyserver pgp.mit.edu --recv-key AED4B06F473041FA

Next add the key to apt-key.

gpg --armor --export AED4B06F473041FA | apt-key add -

Now when running apt-get update the error should be gone

apt-get update