You need to update your ssl security keys and up2date
here is the link to the website for the ssl update if you have no gui use a windows or another linux system to download the files
SSL Connection Errors
On August 28th, the SSL certificates used by up2date, rhn_register, and the RHN applet expired. Systems attempting to connect to RHN using an older certificate will receive 'certificate verify failed' errors. Please see the following instructions to download the latest versions of up2date and rhn_register.