By default RHEL packages are signed with the RH gpg key. Before start the yum installation verifies gpg key.
 

# yum install package_name

Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 DSA/SHA1 Signature, key ID 6b8d79e6: NOKEY
Public key for a52dec-0.7.4-8.el6.rf.x86_64.rpm is not installed

 
Do you want to list of packages key,
 
# rpm -qa gpg-pubkey*

gpg-pubkey-e42d547b-3960bdf1
gpg-pubkey-6b8d79e6-3f49313d
gpg-pubkey-66534c2b-50df7bda
gpg-pubkey-e8562897-459f07a4
gpg-pubkey-6b8d79e6-3f49313d

There are two way solution to fixed this error one is install that key or skip the key check with --nogpgcheck option in yum

solution 1 :

You need to install the Repoforge GPG key:
 
#  rpm --import http://apt.sw.be/RPM-GPG-KEY.dag.txt

or

Solution 2 :

Use --nogpgcheck for disable gpg signature checking
 
# yum install package_name --nogpgcheck