Subversion of online certificate validation processes can enable malicious use of revoked certificates. An attacker who can prevent a certificate from reaching the certificate revocation list can impersonate a legitimate actor and execute malicious activity, while the victim is unaware that he/it is communicating with an illegitimate participant.
Defining certificate authentication policies and procedures is an instrumental part of a public key infrastructure’s (PKI) design. Further, proper execution and enforcement will ensure that revoked certificates — and users — are denied access. While many organizations will use a certificate revocation list (CRL), some might opt for a different approach, such as online certificate status protocol (OCSP) or authentication, authorization and accounting (AAA).
Such decisions need to be part of the initial design discussions based on the needs of the organization. It is worth noting that any private keys deployed in the certificate revocation process need to be protected equally with the keys that form the basis of the issuing process.