Also make sure to verify the fingerprint of the signing key at the following trusted websites (make sure they start with HTTPS), press CTRL+F and paste there the fingerprint and if you find it there, it should be the correct one:
https://bitcoin.org/en/full-node#ubuntu-1410
https://github.com/saivann/bitcoin.org/commit/4d9f830f533c757c149a768daec5621d0fd3a9ca
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-June/009045.html