The NOKEY warning is not really a problem. It won’t prevent you from doing anything.
If you’d like to resolve it, do the following command to get the correct key for the site you’re downloading from:
You must be root to do any of this.
download the appropriate RPM-GPG-KEY and run:
rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY
After you run this, the NOKEY warning will not be displayed.