Active Directory Certificate Services Definition

KZero Staff
Jul 27, 2023

What are Active Directory Certificate Services?

Active Directory (AD) is a Microsoft solution for implementing identity and access management (IAM). It provides various features to an organization, including its Certificate Services (CS).

AD CS is a system for implementing an internal public key infrastructure (PKI) system internal to an organization. This enables an organization to issue internal digital certificates that can be used for encrypted email, digital signatures, and user authentication.

What is PKI?

Digital certificates are designed to tie a user’s identity to a public key. This public key can then be used to send encrypted messages to the user or verify the integrity and authenticity of data via digital signatures.

The main challenge of digital certificates is proving their authenticity and that the provided public key actually belongs to the alleged owner. PKI solves this problem by creating a hierarchy where verification flows down from a trusted root certificate authority (CA) to the end user’s digital certificate via a chain of trust.

A computer can be configured to implicitly trust a particular root CA, including both internal and external root CAs. These root CAs can then generate digital certificates for various entities by verifying their identity and signing a digital certificate with the root CA’s private key. These digital certificates contain public keys that can be used for various purposes, including verifying the digital signatures on digital certificates generated by this entity.

In a PKI infrastructure, each user will have a digital certificate that is linked to a root CA via a chain of digitally-signed digital certificates. If every signature validates, the root CA is trusted, and the certificate isn’t expired or revoked, then the digital certificate and the public key it contains are trusted.

How Does AD CS Work?

The digital certificates used to verify the identity of websites on the Internet are generated by public root CAs. However, an organization can implement an internal PKI system using Active Directory Certificate Services.

AD CS enables an organization to create an internal root CA and issue digital certificates for their AD environment. These digital certificates work the same as those generated by an external root CA except for the fact that they have an internal root CA. This means that only systems and software configured to trust this root CA will accept the digital certificates that it accepts.

AD CS also handles the other management aspects of PKI. For example, it is responsible for checking if a certificate has been revoked and for updating digital certificates when they expire.

Use Cases for AD CS Certificates

The digital certificates generated by AD CS are intended for use within an organization’s environment. Some common use cases include:

  • Encrypted Email: Public keys are commonly used for encrypted email systems. With a digital certificate, a user can encrypt a message to the recipient that can only be decrypted and read using the private key.
  • Digital Signatures: Digital signatures are generated with a private key and verified using the public contained within a digital certificate. These signatures prove the integrity and authenticity of signed data.
  • User Authentication: The public keys contained in digital certificates can be used for user authentication. The user will digitally sign some data with their private key, which the application verifies using their public key.


Active Directory Certificate Services enables organizations to set up PKI within an enterprise. This has numerous potential applications, including encrypted email, digital signatures, and user authentication.

KZero Staff

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