debian NO_PUBKEY AAFF4A5B336064B5

error message:

W: GPG error: http://deb.opera.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AAFF4A5B336064B5


reason:
key is outdated


solution:
wget -O - http://deb.opera.com/archive.key | sudo apt-key add -