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The Online Certificate Status Protocol (OCSP) is an Internet protocol used for obtaining the revocation status of an X.509 digital certificate. [2] It is described in RFC 6960 and is on the Internet standards track.
Browsers and other relying parties might use CRLs, or might use alternate certificate revocation technologies (such as OCSP) [4] [5] or CRLSets (a dataset derived from CRLs [6]) to check certificate revocation status. Note that OCSP is falling out of favor due to privacy and performance concerns. [7] [8] [9] Subscribers and other parties can ...
OCSP stapling is designed to reduce the cost of an OCSP validation, both for the client and the OCSP responder, especially for large sites serving many simultaneous users. However, OCSP stapling supports only one OCSP response at a time, which is insufficient for certificate chains with intermediate CA certs. [26] [27]
OCSP suffers from scalability issues. It relies on the client having network access at the time of checking the certificate's revocation status; further, the OCSP responder must be accessible and produce usable responses, or else the check will fail and the client must choose between failing-soft and failing-hard.
X.509 and RFC 5280 also include standards for certificate revocation list (CRL) implementations. Another IETF-approved way of checking a certificate's validity is the Online Certificate Status Protocol (OCSP). Firefox 3.0 enabled OCSP checking by default, as did versions of Windows from at least Vista and later. [9]
Without revocation, an attacker would be able to exploit such a compromised or misissued certificate until expiry. [31] Hence, revocation is an important part of a public key infrastructure. [32] Revocation is performed by the issuing CA, which produces a cryptographically authenticated statement of revocation. [33]
Certificate authorities are also responsible for maintaining up-to-date revocation information about certificates they have issued, indicating whether certificates are still valid. They provide this information through Online Certificate Status Protocol (OCSP) and/or Certificate Revocation Lists (CRLs).
Certificates that support certificate transparency must include one or more signed certificate timestamps (SCTs), which is a promise from a log operator to include the certificate in their log within a maximum merge delay (MMD). [4] [3] At some point within the maximum merge delay, the log operator adds the certificate to their log.