Here are some references on credential revocation:

1. Certificate revocation list
2. Online Certificate Status Protocol
3. OCSP Stapling
4. Server-based Certificate Validation Protocol (SCVP)
5. OpenCA OCSP Responder
6. Public-key cryptography
7. OpenCA PKI
8. EJBCA

 Here are some references on renewing certificates:

1. A nice discussion on renewing root CA