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Security Fundamentals & Crypto · Foundational

Wildcard Certificate

Certificate that secures all first-level subdomains of a domain using an asterisk, such as *.example.com.

Definition

A wildcard certificate covers www.example.com and mail.example.com but not example.com itself or deeper levels like a.b.example.com unless listed separately. It simplifies management but increases risk because one compromised key affects all covered subdomains. Public wildcard certificates cannot be Extended Validation.

Example

*.example.com secures shop.example.com and api.example.com with one key pair.

Exam tip

Wildcards cover one level only; know the security trade-off of a shared private key.

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