SSL Checker

SSL Checker

SSL Checker is a tool that allows you to investigate if the SSL Certificate for a given website is valid. The tool also  displays the DNS names on the certificates as well as the creation and expiration dates. 

SSL certificate validation plays a critical role in establishing secure connections over the Internet. When a user connects to a website, the SSL/TLS protocols are employed by both the browser and server. The SSL certificate acts as a digital credential, verifying the identity of the website. Certificates have a defined validity period, typically lasting from months to years, indicated by the expiration date. The use of expired certificates often leads to error messages or security warnings, discouraging users from visiting the site. Thus, maintaining valid certificates on web servers is vital. Certificate renewal involves obtaining a new SSL certificate and replacing the expiring one on the server.

An SSL certificate clearly identifies the domain for which it is issued, such as www.example.com. Frequently, a single certificate serves multiple domains, subdomains, or sites.   Such certificates are known as SAN certificates (Subject Alternative Names). SAN is an extension to the X.509 specification that allows a SSL certificate to specify multiple host names.  SAN certificates provide flexibility and improve efficiency by reducing the need for multiple certificates.

A wildcard SSL certificate offers an alternative method to secure a domain and its subdomains with a single certificate. Unlike a standard SSL certificate, which is issued for a specific domain (e.g., www.example.com), a wildcard certificate is issued for a domain and all its subdomains (e.g., *.example.com). The wildcard character (*) is used to represent any subdomains under the specified domain. For instance, a certificate for *.example.com covers subdomains like blog.example.com and shop.example.com. However, it does not cover the 2nd-level subdomains (e.g., my.blog.example.com). To include these, a separate wildcard certificate or an additional SAN entry for *.blog.example.com would be required. 

See Also:

Qualys SSL Server Test