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What Is a Wildcard SSL Certificate?
If you manage a website — or several — you have likely come across the term SSL certificate. These digital certificates are essential for securing online communications, protecting sensitive data, and building trust with your visitors. But as websites grow in complexity, a standard SSL certificate may not always be the most practical solution. That is where a wildcard SSL certificate comes in.
In this guide, we will explain exactly what a wildcard SSL certificate is, how it works, when you should use one, and what its limitations are. Whether you are a business owner, a web developer, or simply someone trying to make sense of website security, this article will give you a clear and thorough understanding of the topic.
Understanding SSL Certificates
Before diving into wildcard SSL certificates specifically, it helps to understand what an SSL certificate actually does. SSL stands for Secure Sockets Layer, though the technology has largely been superseded by TLS (Transport Layer Security). Despite this, the term SSL remains widely used.
An SSL certificate is a digital document that authenticates the identity of a website and enables an encrypted connection between a user’s browser and the web server. When a website has a valid SSL certificate, the URL begins with https:// rather than http://, and a padlock icon appears in the browser’s address bar. This reassures visitors that their data — including passwords, payment details, and personal information — is being transmitted securely.
Standard SSL certificates are issued for a single domain name, such as www.example.com. This works perfectly well for many websites, but organisations that operate multiple subdomains face a challenge: they would need to purchase and manage a separate certificate for each one.
What Is a Wildcard SSL Certificate?
A wildcard SSL certificate is a type of SSL/TLS certificate that secures a single domain and an unlimited number of its first-level subdomains with just one certificate. The term “wildcard” refers to the asterisk (*) used in the certificate’s common name, which acts as a placeholder for any subdomain.
For example, a wildcard SSL certificate issued for *.example.com would automatically cover:
- www.example.com
- mail.example.com
- shop.example.com
- blog.example.com
- portal.example.com
Any subdomain at the first level beneath the root domain would be protected under the same certificate. This makes wildcard SSL certificates an extremely efficient and cost-effective solution for organisations that need to secure multiple subdomains simultaneously.
How Does a Wildcard SSL Certificate Work?
The mechanics behind a wildcard SSL certificate are similar to those of a standard certificate. When a browser connects to a secured website, it checks the certificate to verify that it is valid, issued by a trusted Certificate Authority (CA), and matches the domain name in question.
With a wildcard certificate, the asterisk in the common name instructs the browser to accept any subdomain in that position. So when a user visits shop.example.com, the browser checks the certificate, sees that it is valid for *.example.com, and confirms that shop matches the wildcard. The encrypted connection is then established seamlessly.
Domain Validation vs Organisation Validation
Wildcard SSL certificates are available at two primary validation levels. Domain Validation (DV) certificates are the quickest to obtain and simply verify that the applicant controls the domain. Organisation Validation (OV) certificates require additional checks, including verification of the organisation’s legal identity, making them more suitable for businesses that want to display a higher level of credibility. It is worth noting that Extended Validation (EV) certificates are not available in wildcard form.
When Should You Use a Wildcard SSL Certificate?
A wildcard SSL certificate is the right choice in several common scenarios. If your website relies on multiple subdomains — for instance, separate subdomains for a blog, a customer portal, an e-commerce shop, and a support centre — managing individual certificates for each would be time-consuming and expensive. A single wildcard certificate simplifies administration considerably.
They are also ideal for businesses that regularly create new subdomains, such as those offering Software as a Service (SaaS) products where each customer might be assigned their own subdomain. Rather than issuing a new certificate every time a subdomain is created, the wildcard certificate covers them all automatically.
For further reading on managing digital infrastructure efficiently, take a look at the DA Manager blog, which offers practical insights for website and domain administrators.
Limitations of Wildcard SSL Certificates
While wildcard SSL certificates offer significant advantages, they are not without their limitations. Understanding these drawbacks will help you decide whether a wildcard certificate is truly the best option for your needs.
First-Level Subdomains Only
A wildcard SSL certificate only covers first-level subdomains. This means that a certificate for *.example.com would not cover mail.shop.example.com, which is a second-level subdomain. If you need to secure nested subdomains, you would require either a separate certificate or a multi-domain (SAN) certificate.
Security Considerations
Because a single private key is associated with the wildcard certificate and used across multiple servers and subdomains, a security breach on one server could potentially compromise all subdomains covered by that certificate. Careful key management and robust server security practices are essential when using wildcard certificates.
No Extended Validation
As mentioned earlier, EV certificates — which display the organisation’s name prominently in some browsers and are considered the gold standard for high-trust websites such as banking portals — are not available in wildcard format. If your organisation requires EV certification, you will need to obtain individual certificates for each subdomain.
Wildcard SSL Certificates vs Multi-Domain (SAN) Certificates
Another option worth considering is the multi-domain SSL certificate, also known as a Subject Alternative Name (SAN) certificate. Whilst a wildcard certificate covers unlimited subdomains of a single domain, a SAN certificate can cover multiple entirely different domain names — for example, example.com, anotherexample.co.uk, and thirdexample.net — all under one certificate.
The right choice depends on your specific requirements. If you have many subdomains under one domain, a wildcard certificate is likely the better fit. If you manage several distinct domains, a SAN certificate may be more appropriate. In some cases, a combination of both approaches is used.
How to Obtain a Wildcard SSL Certificate
Obtaining a wildcard SSL certificate follows a process similar to acquiring any other type of SSL certificate. You will need to:
- Choose a reputable Certificate Authority (CA) such as DigiCert, Sectigo, or Let’s Encrypt.
- Generate a Certificate Signing Request (CSR) on your web server, specifying the wildcard domain (e.g., *.example.com).
- Submit the CSR to your chosen CA and complete the validation process.
- Install the issued certificate on your web server.
- Configure your server to use the certificate across all relevant subdomains.
Let’s Encrypt, a free and widely used CA, supports wildcard certificates via the ACME protocol with DNS-based validation, making it an accessible option for those on a budget.
Final Thoughts
A wildcard SSL certificate is a powerful and practical tool for any organisation managing multiple subdomains under a single domain. It simplifies certificate management, reduces costs, and ensures that all your subdomains benefit from the same level of encryption and trust. However, it is important to be aware of its limitations — particularly regarding second-level subdomains, security key management, and the absence of Extended Validation options.
By understanding exactly what a wildcard SSL certificate is and how it works, you can make a well-informed decision about the right security solution for your website infrastructure. Whether you opt for a wildcard certificate, a SAN certificate, or individual certificates for each domain, the most important thing is that your website and its users remain protected at all times.
