Subject Alternative Name Explained

Subject Alternative Name (SAN) is an extension to X.509 that allows various values to be associated with a security certificate using a subjectAltName field.^[1] These values are called Subject Alternative Names (SANs). Names include:^[2]

• Email addresses
• IP addresses
• URIs
• DNS names: this is usually also provided as the Common Name RDN within the Subject field of the main certificate.
• Directory names: alternative Distinguished Names to that given in the Subject.
• Other names, given as a General Name or Universal Principal Name: a registered object identifier followed by a value.

(May 2000) specifies Subject Alternative Names as the preferred method of adding DNS names to certificates, deprecating the previous method of putting DNS names in the commonName field.^[3] Google Chrome version 58 (March 2017) removed support for checking the commonName field at all, instead only looking at the SANs.

See also

• Wildcard certificate

Notes and References

1. Web site: x509v3_config - X509 V3 certificate extension configuration format. OpenSSL. 2020-01-16.

2. 4.2.1.6. Subject Alternative Name

3. Web site: Deprecations and Removals in Chrome 58 . Medley . Joseph . March 2017 . Google Developers . 2022-01-04 .