$ sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 16126D3A3E5C1192

(output suppressed)

$ sudo apt-get update

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://za.archive.ubuntu.com trusty Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: Failed to fetch http://za.archive.ubuntu.com/ubuntu/dists/trusty/Release  

W: Some index files failed to download. They have been ignored, or old ones used instead.