The gpgcheck option, found in the main section of the /etc/yum.conf file determines if an RPM package's signature is always checked prior to its installation. Rationale: It is important to ensure that an RPM's package signature is always checked prior to installation to ensure that the software is obtained from a trusted source.
Solution
Edit the /etc/yum.conf file and set the gpgcheck to 1 as follows: gpgcheck=1