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Certificate authority (CA) software is the software and supporting equipment used to operate a certificate authority within a public key infrastructure (PKI). It supports workflows such as processing certificate requests, applying policy, issuing certificates, and managing renewal and revocation. The certificate authority is the entity with final authority to create a certificate; its software is the equipment that helps carry out that role.
What is a certificate authority in a PKI?
A PKI defines the participants, trust relationships, certificate policies, and operating practices used to issue and rely on digital certificates. A certificate binds information—such as a name or domain—to a public key. The CA issues and signs that certificate, and relying parties check it when deciding whether to trust or use the key.
The distinction between the authority and its implementation matters. RFC 9810 defines the CA as the entity responsible for issuing certificates and distinguishes it from the “CA equipment” used to implement the function. That equipment may include online and offline components. One possible arrangement keeps the CA private key available only to an offline component, but RFC 9810 leaves architecture choices to implementation and policy rather than requiring that design.
What does CA software do?
Capabilities depend on the product and deployment, but CA software can support certificate request processing, policy and certificate profiles, certificate signing, enrollment interfaces, publication of certificates and status information, renewal or re-key, revocation, and operational records. The wider operation also involves decisions and controls around identity validation, key generation and protection, auditing, and archiving.
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Issuance is not simply an automatic copy of a request. RFC 9810 states that “Final authority for certification creation rests with the CA.” The CA may change requested certificate fields or extensions in accordance with its operating policy.
Enrollment and automation
Enrollment methods vary. ACME, specified in RFC 8555, automates domain-control validation and certificate issuance and includes certificate-management functions such as revocation. It is one protocol used in Web PKI automation, not the only way to request certificates and not evidence that every CA product supports ACME.
Lifecycle and operational controls
Issuing a certificate is only one part of running a CA. RFC 3647 provides a framework for certificate policies and certification practices. Its topics include identification and authentication, lifecycle requirements, facilities and operational controls, technical security controls, and profiles for certificates, certificate revocation lists (CRLs), and Online Certificate Status Protocol (OCSP) responses. It is a framework, not a mandatory product checklist or a prescription for one particular certificate policy.
How the CA, RA, software, and HSM differ
| Term | Role | How it relates to CA software |
|---|---|---|
| Certificate authority (CA) | The entity that has final authority to create and issue certificates. | The CA’s role is implemented using CA equipment, which can include software and other components. |
| Registration authority (RA) | May perform delegated tasks such as identity checks, request checks, revocation reporting, or name assignment. | It can handle parts of enrollment or validation, but its delegated responsibilities depend on the environment. The CA retains final authority over certificate creation. |
| CA software | Supports the operation of the CA and its certificate workflows. | It is implementation equipment, not the authority itself. |
| Hardware security module (HSM) | Dedicated hardware that can protect cryptographic keys and perform cryptographic operations. | It is a separate, optional component that may protect CA private keys. Compatibility and configuration depend on the CA software and HSM. |
| Certificate lifecycle management | The broader set of practices and systems used to manage certificates from enrollment through renewal or revocation. | CA software may support lifecycle workflows, but the term does not mean the same thing as the CA itself or its issuing software. |
Examples of CA software
EJBCA
EJBCA’s official material describes its Community edition as open-source PKI software and also offers a commercial Enterprise edition. The vendor describes CA, RA, and validation functions, multiple enrollment protocols and integration interfaces, and use cases including internal PKI, industrial environments, IoT, and DevOps. These are vendor descriptions, not an independent assessment of how well a deployment will meet a particular organization’s needs. The vendor describes Enterprise deployment options that include cloud, SaaS, and appliance models.
Microsoft Active Directory Certificate Services
Microsoft documents Active Directory Certificate Services (AD CS) as a Windows Server role service that can configure a server to act as a CA. Microsoft’s installation documentation lists Windows Server 2025, 2022, 2019, and 2016; check the current Microsoft documentation for version coverage and prerequisites before planning an installation.
These examples have different deployment and licensing models. A product name alone does not establish whether a CA is suitable for a particular PKI.
How to evaluate CA software
Compare products against the architecture and work your organization actually needs to support. The following questions are evaluation criteria, not a claim that every product provides every capability.
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- Environment: Is the PKI primarily Windows-domain, cross-platform, cloud, appliance-based, or embedded in an industrial or IoT environment?
- Scale and topology: How many root and issuing CAs are needed? Does the design separate offline and online roles?
- Workflows and integration: Which enrollment protocols, directories, APIs, client platforms, and validation steps must work?
- Key security: How will CA keys be generated, protected, backed up, recovered, and used? Who approves sensitive actions?
- Lifecycle visibility: How will the organization track issuance, renewal, revocation, CRL or OCSP publication, audit records, and certificate inventory?
- Operations and support: Can the team operate the chosen design? Is community support sufficient, or are vendor support and service commitments required?
- Cost and licensing: Verify current licensing, infrastructure, deployment, and staffing costs directly; they vary and are not established by the cited product descriptions.
When an HSM is part of the design
An HSM is hardware, not CA software, and a CA does not universally require one. Microsoft’s guidance describes HSMs as secure hardware stores for CA keys that can also provide dedicated cryptographic processing. Documented form factors include PCI adapters, network appliances, serial devices, and USB devices; a network HSM may be shared among multiple CAs.
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Microsoft advises installing and configuring an HSM before setting up a CA whose keys will be stored on it. Confirm that a specific HSM is supported by the chosen CA software and suits the organization’s security and operational requirements. A generic consumer USB token should not be assumed to be an appropriate substitute for a CA HSM.
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