X.509 Extensions

Certificate extensions were introduced in version 3 of the X.509 standard for certificates. These v3 extensions allow certificates to be customized to applications by supporting the addition of arbitrary fields in the certificate. X.509 v3 extensions provide for the association of additional attributes with users or public keys. Each extension, identified by its OID (Object Identifier), is marked as “Critical” or “Non-Critical,” and includes the extension-specific data.