Editing Public key infrastructure (section)

==== Certificate revocation ====
{{main|Certificate revocation}}
A certificate may be revoked before it expires, which signals that it is no longer valid. Without revocation, an attacker would be able to exploit such a compromised or mis-issued certificate until expiry.{{sfn|Smith|Dickinson|Seamons|2020|p=1}} Hence, revocation is an important part of a public key infrastructure.{{sfn|Sheffer|Saint-Andre|Fossati|2022|loc=7.5. Certificate Revocation}} Revocation is performed by the issuing [[certificate authority]], which produces a [[cryptographically authenticated]] statement of revocation.{{sfn|Chung|Lok|Chandrasekaran|Choffnes|2018|p=3}}

For distributing revocation information to clients, timeliness of the discovery of revocation (and hence the window for an attacker to exploit a compromised certificate) trades off against resource usage in querying revocation statuses and privacy concerns.{{sfn|Smith|Dickinson|Seamons|2020|p=10}} If revocation information is unavailable (either due to accident or an attack), clients must decide whether to ''fail-hard'' and treat a certificate as if it is revoked (and so degrade [[availability]]) or to ''fail-soft'' and treat it as unrevoked (and allow attackers to sidestep revocation).{{sfn|Larisch|Choffnes|Levin|Maggs|2017|p=542}}

Due to the cost of revocation checks and the availability impact from potentially-unreliable remote services, [[Web browsers]] limit the revocation checks they will perform, and will fail-soft where they do.{{sfn|Smith|Dickinson|Seamons|2020|p=1-2}} [[Certificate revocation lists]] are too bandwidth-costly for routine use, and the [[Online Certificate Status Protocol]] presents connection latency and privacy issues. Other schemes have been proposed but have not yet been successfully deployed to enable fail-hard checking.{{sfn|Sheffer|Saint-Andre|Fossati|2022|loc=7.5. Certificate Revocation}}