CentOS yum package not signed

La configuración por defecto de CentOS obliga a que los paquetes que vayamos a instalar estén firmados con GPG. Cuando el paquete no está firmado como es el siguiente caso, el instalador se queja y no nos permite:

# yum install Nessus-3.2.1-es5.i386.rpm
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Reading repository metadata in from local files
Parsing package install arguments
Examining Nessus-3.2.1-es5.i386.rpm: Nessus - 3.2.1-es5.i386
Marking Nessus-3.2.1-es5.i386.rpm to be installed
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Package Nessus.i386 0:3.2.1-es5 set to be updated
--> Running transaction check

Dependencies Resolved

=============================================================================
 Package                 Arch       Version          Repository        Size
=============================================================================
Installing:
 Nessus                  i386       3.2.1-es5        Nessus-3.2.1-es5.i386.rpm   59 M

Transaction Summary
=============================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total download size: 59 M
Is this ok [y/N]: y
Downloading Packages:


Package Nessus-3.2.1-es5.i386.rpm is not signed

Para conseguir la instalación tan solo tenemos que deshabilitar en la configuración el chekeo de gpg: editamos "/etc/yum.conf" configurando el parametro "gpgcheck=0".
Ahora ya permitirá la instalación correctamente.