What is the function of a Subject Alternative Name (SAN) extension in multi-domain certificates?

The Subject Alternative Name (SAN) extension in multi-domain certificates is designed to identify all domain names owned by a single organization. This functionality enables a single SSL/TLS certificate to secure multiple domain names, rather than requiring separate certificates for each domain. By including additional domain names in the SAN fields of the certificate, the organization can simplify certificate management while ensuring that all specified domains are covered under the same encryption and trust model.

This is particularly beneficial for organizations that operate multiple websites, as it provides flexibility and efficiency in maintaining secure communications across different platforms. The use of SANs also centralizes management, meaning that renewal and updates can be performed more easily without the need to track many individual certificates.

The other options detail different functionalities or misconceptions about SSL/TLS certificates. For instance, securing only a single domain is contrary to the purpose of SANs, as they specifically allow for multiple domains. While subdomains can be included in SANs, they aren't unlimited, and the extension's primary purpose is not focused on subdomain management alone. Lastly, enhancing standard encryption does not accurately describe the role of SANs; its main function is to provide a means to list multiple domains within a certificate rather than directly affecting the cryptographic strength of the encryption itself.