A separate PKI is a distinct public key infrastructure used for a specific environment, such as OT or IT. Splitting trust domains can reduce cascading failures, simplify governance boundaries, and limit the impact of certificate issues. It still requires disciplined enrollment, renewal, revocation, and policy management.
Expanded Definition
A separate PKI is not just a different certificate store. It is a deliberately isolated trust system with its own issuing hierarchy, policy decisions, revocation processes, and operational ownership for a defined environment such as OT, IT, or a regulated business unit. The boundary matters because certificate trust is transitive: once one CA hierarchy is treated as trusted, mis-issuance or compromise can spread far beyond the original scope.
Guidance versus consensus: there is broad agreement that separation improves containment, but there is no single universal design. Some organisations separate by environment, others by business risk, and others by lifecycle or regulatory boundary. The common misunderstanding is to treat “separate PKI” as a naming convention rather than a control boundary. In practice, the separation is only meaningful if policy, issuance authority, and recovery procedures are also split.
For machine and service certificates, separation often becomes a governance decision as much as a technical one. The main question is not whether certificates can be issued, but which trust domain should be able to validate them and under what operating assumptions.
Examples and Use Cases
Separate PKI appears wherever one certificate trust domain would create too much shared exposure across environments. It is most useful when different systems have different uptime expectations, device constraints, or trust rules.
- An OT environment uses its own CA chain so plant systems do not depend on the same certificate services as corporate IT.
- A production application platform keeps workload certificates separate from developer and test certificates to avoid accidental trust expansion.
- A regulated business unit runs a dedicated PKI so certificate policy, key protection, and audit ownership remain clearly scoped.
- A partner integration uses a bounded trust hierarchy so external certificates cannot be validated by the organisation’s broader internal pki.
- A machine identity programme separates issuing paths for human users and automated services because their renewal, revocation, and lifecycle controls differ.
The trade-off is operational overhead. More PKI domains mean more policy alignment, more renewal discipline, and more recovery planning, but they also reduce the chance that one certificate failure affects every connected system.
Security Implications
The security value of a separate PKI is containment. If one issuing chain is misconfigured, exposed, or unavailable, the failure should stay within that trust domain instead of becoming a broad authentication or signing outage. That matters because certificate problems are not always loud: broken enrollment can surface as failed service startup, expired workloads, mutual TLS failures, or trust-chain mismatches long after the root cause.
Mismanaged separation creates its own risk. If administrators duplicate trust roots too freely, the organisation ends up with the appearance of separation but not the actual blast-radius reduction. If revocation and renewal are handled inconsistently across domains, one PKI may become easier to compromise while another is over-restricted and operationally brittle.
For NHIMG readers, the practical signal is that certificate scope and ownership should match the trust boundary being defended. A separate PKI only improves resilience when it is supported by disciplined lifecycle control and clear recovery responsibilities.
Domain and Governance Relevance
Separate PKI is especially relevant in identity-heavy environments because certificates are frequently used as machine identities, service identities, or authorization anchors. In those settings, the PKI is not merely infrastructure support; it becomes part of who or what is trusted to act. That changes governance: the issuing authority, approval path, renewal ownership, and revocation response all become control decisions that affect access and continuity.
In NHI-oriented environments, separation helps prevent one certificate lifecycle problem from cascading across every workload, API client, or automation account that relies on the same trust root. It also makes accountability clearer when different teams manage different environments, because ownership follows the trust domain rather than the technology stack alone.
Where separate PKI is used for OT, regulated services, or high-value automation, the key governance question is whether the trust boundary is real in practice. If cross-signing, shared admin access, or uncontrolled root distribution exists, the organisation has weakened the separation it intended to create.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 and MITRE ATT&CK address the attack and risk surface, while CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-01 — Inventory and Ownership | Separate PKI governs machine and service certificate ownership across trust domains. |
| Recommendation — Inventory each PKI domain and assign clear ownership for issuance, renewal, and revocation. | ||
| CIS Controls v8 | 5 — Account Management | PKI separation changes how identities and access paths are governed across environments. |
| Recommendation — Restrict certificate-admin and trust-root access to the smallest necessary operator set. | ||
| NIST CSF 2.0 | PR.AC-1 — Identity and Credentials | PKI separation is a trust and credential boundary that supports access control. |
| PR.DS-6 — Data-at-Rest Protection | Private keys and CA material in separate PKIs need distinct protection assumptions. | |
| Recommendation — Define trust-domain boundaries so certificate validation stays limited to intended systems. Protect CA keys and signing material according to the sensitivity of each PKI domain. | ||
| MITRE ATT&CK | T1552 — Unsecured Credentials | Compromised PKI secrets can collapse the intended isolation between trust domains. |
| Recommendation — Hunt for exposed CA keys and revoke trust if signing material is found outside protected storage. | ||
Related resources from NHI Mgmt Group
- Should organisations manage FIDO2 and PKI in separate programmes?
- What breaks when organisations manage PKI certificates and FIDO2 passkeys in separate workflows?
- Should organisations build separate controls for AI agent deployments?
- What is the difference between converged identity governance and separate IGA and PAM tools?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 7, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
