Operational Protocols

Internet X.509 PKI - Online Certificate Status Protocol (OCSP)
The PKIX document specifies a protocol useful in determining the current status of a digital certificate without requiring CRLs.
http://tools.ietf.org/html/rfc2560

RFC 2585 - Internet X.509 PKI - FTP and HTTP
The PKIX standard specifies the conventions for using the FTP and the HTTP to obtain certificates and certificate revocation lists (CRLs) from PKI repositories.
http://tools.ietf.org/html/rfc2585

RFC 2559 - Internet X.509 PKI - LDAPv2
The PKIX standard describes the LDAPv2-based protocol to provide access to PKI repositories for the purposes of retrieving and managing PKI information.
http://tools.ietf.org/html/rfc2559