CentOS had an update for the nss-softokn package – nss-softokn-3.14.3-19
However, nss-softokn-3.14.3-19 needs nss-softokn-freebl-3.14.3-19 to operate properly, and vice versa, but those packages do not have checks in place to make sure that a matching version of the other package are also installed.
Thus if you yum update only installed one of the packages you will end up with a broken YUM and RPM.
You might see error messages like these when trying to run YUM and RPM commands:
error: rpmts_HdrFromFdno: Header V3 RSA/SHA1 Signature, key ID xxx BAD
error: rpmdbNextIterator: skipping h# 1784 Header V3 RSA/SHA1 Signature, key ID xxx BAD
Most of the time you will have had nss-softokn-3.14.3-19 installed but not nss-softokn-freebl-3.14.3-19
To fix this on CentOS 6.6 64 Bit you have to:
Manually download nss-softokn-freebl-3.14.3-19
Extract the RPM
rpm2cpio nss-softokn-freebl-3.14.3-19.el6_6.x86_64.rpm | cpio -idmv
Copy .libfreeblpriv3.* to correct location
cp ./lib64/libfreeblpriv3.* /lib64
Rerun Yum Update to update nss-softokn-freebl and FIX YUM and RPM