Contact Us

What is a Subordinate CA? (What is an Issuing CA?)

What is a Subordinate Certificate Authority? What is an Issuing CA?
21 Nov 2023

What is a Subordinate Certificate Authority?

In a Two-Tier PKI Hierarchy, which is the recommended structure employed in certificate management, two main types of certificate authorities (CAs) emerge: the root CA and the subordinate CA, also known as the issuing CA. While the root CA is the primary trust anchor and sits at the pinnacle of this hierarchy, the subordinate CA plays a more nuanced and specific role.

The issuing CA acts as the primary entity for distributing certificates to end users. The reason it’s dubbed “subordinate” or “issuing” is because it operates (issues certificates) under the trust umbrella of the root CA. For the certificates it issues to be trusted, the root CA must sign the subordinate CA. This signing process effectively ensures that any certificate issued by the subordinate CA inherits the trustworthiness of the root certificate authority.

“Should I Have Multiple Issuing CAs?”

While a singular root CA can be associated with several subordinate or issuing CAs, best practices advocate for segmenting these subordinate CAs based on the nature of certificates they distribute. For instance, if your organization is dealing with both Smartcard certificates and SSL certificates, it’s wise to have separate subordinate CAs for each. This delineation simplifies management, ensures better security, and aids in tracking and auditing.

Beyond the type of certificate, there are other reasons to consider having multiple subordinate CAs:


As your organization grows, so do its certificate needs. Multiple CAs can cater to a higher volume of certificate requests and higher availability needs, ensuring that your operations run smoothly without delays.


For global businesses, it makes sense to have subordinate CAs located in various geographical regions. This ensures that if one CA faces issues due to regional disruptions, others can continue to issue certificates without hindrance.

Why are Subordinate CAs Important?

Understanding the role and importance of a subordinate CA is vital for anyone delving into the world of PKI. By acting as the direct link between the trust anchor (root CA) and the end users, subordinate CAs ensure that digital certificates are issued swiftly and securely. To learn more about how they interact, check out this blog that outlines the difference between a root CA and an issuing CA. Whether you’re considering setting up a new PKI hierarchy or refining an existing one, ensuring an optimal structure of subordinate CAs can make a significant difference in your organization’s digital security landscape.

You Might Also Want to Read