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A wildcard certificate is a digital public key document that can be applied to a domain and subdomains. It has the advantage of simultaneously covering an unlimited number of first-level subdomains and is, thus, more cost-effective and convenient with the increase of subdomains.
A wildcard certificate is also known as a wildcard Secure Sockets Layer (SSL) certificate.
A wildcard certificate may be applied to multiple first-level subdomains of a website or single domain. It secures the common domain name and all subdomains at the level specified during the request to the certification authority (CA), but it usually is applied to first-level subdomains. This means that a SSL certificate with a common name, like *.sampledomain.com, can be used without errors when it is used for any domain names that replaces the * character.
However, wildcard certificates only work for single-level, versus multiple-level, subdomains. Unified Communications Certificates (UCC SSL) are used to secure multiple levels of subdomains or totally different domains.
In the given example, a wildcard certificate works for:
However, a wildcard certificate does not work for: