1.4. Certificate Life Cycle

Certificates are used in many applications, from encrypting email to accessing websites. There are two major stages in the lifecycle of the certificate: the point when it is issued (issuance and enrollment) and the period when the certificates are no longer valid (renewal or revocation). There are also ways to manage the certificate during its cycle. Making information about the certificate available to other applications is publishing the certificate and then backing up the key pairs so that the certificate can be recovered if it is lost.

1.4.1. Certificate Issuance

The process for issuing a certificate depends on the CA that issues it and the purpose for which it will be used. Issuing non-digital forms of identification varies in similar ways. The requirements to get a library card are different than the ones to get a driver's license. Similarly, different CAs have different procedures for issuing different kinds of certificates. Requirements for receiving a certificate can be as simple as an email address or user name and password to notarized documents, a background check, and a personal interview.
Depending on an organization's policies, the process of issuing certificates can range from being completely transparent for the user to requiring significant user participation and complex procedures. In general, processes for issuing certificates should be flexible, so organizations can tailor them to their changing needs.

1.4.2. Certificate Expiration and Renewal

Like a driver's license, a certificate specifies a period of time during which it is valid. Attempts to use a certificate for authentication before or after its validity period will fail. Managing certificate expirations and renewals are an essential part of the certificate management strategy. For example, an administrator may wish to be notified automatically when a certificate is about to expire so that an appropriate renewal process can be completed without disrupting the system operation. The renewal process may involve reusing the same public-private key pair or issuing a new one.
Additionally, it may be necessary to revoke a certificate before it has expired, such as when an employee leaves a company or moves to a new job in a different unit within the company.
Certificate revocation can be handled in several different ways:
Verify if the certificate is present in the directory
Servers can be configured so that the authentication process checks the directory for the presence of the certificate being presented. When an administrator revokes a certificate, the certificate can be automatically removed from the directory, and subsequent authentication attempts with that certificate will fail, even though the certificate remains valid in every other respect.
Certificate revocation list (CRL)
A list of revoked certificates, a CRL, can be published to the directory at regular intervals. The CRL can be checked as part of the authentication process.
Real-time status checking
The issuing CA can also be checked directly each time a certificate is presented for authentication. This procedure is sometimes called real-time status checking.
Online Certificate Status Protocol
The Online Certificate Status Protocol (OCSP) service can be configured to determine the status of certificates.
For more information about renewing certificates, see Section 2.4.2, “Renewing Certificates”. For more information about revoking certificates, including CRLs and OCSP, see Section 2.4.4, “Revoking Certificates and Checking Status”.