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CRL for a revoked cert of Verisign CA. There are two different states of revocation defined in RFC 5280: Revoked A certificate is irreversibly revoked if, for example, it is discovered that the certificate authority (CA) had improperly issued a certificate, or if a private-key is thought to have been compromised.
Since an OCSP response contains less data than a typical certificate revocation list (CRL), it puts less burden on network and client resources. [10]Since an OCSP response has less data to parse, the client-side libraries that handle it can be less complex than those that handle CRLs.
A certificate revocation list (CRL) enumerates revoked certificates. They are cryptographically authenticated by the issuing CA. [29] CRLs have scalability issues, and rely on the client having enough network access to download them prior to checking a certificate's status. [9]
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]
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]
The dominant method used for this purpose is to host a certificate revocation list (CRL) for download via the HTTP or LDAP protocols. To reduce the amount of network traffic required for certificate validation, the OCSP protocol may be used instead.
A drawback to offline operation is that hosting of a certificate revocation list by the root CA is not possible (as it is unable to respond to CRL requests via protocols such as HTTP, LDAP or OCSP). However, it is possible to move certificate validation functionality into a dedicated validation authority authorized by the offline root CA.
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.