The Ultimate Certificate Authority Security Assessment Checklist for 2025

Public Key Infrastructure (PKI) and Certificate Authorities (CAs) are undergoing a massive, forced transformation. The days of treating your CA as a "set it and forget it" piece of legacy infrastructure are over.

Between Google Chrome’s impending push to reduce maximum public TLS certificate lifecycles to 90 days, the finalization of Post-Quantum Cryptography (PQC) standards, and the explosive sprawl of machine identities across Kubernetes clusters and service meshes, manual certificate management is now a critical security liability.

Furthermore, 2024 proved that even the largest commercial CAs are not immune to catastrophic failures. The highly publicized distrust of Entrust by major browser vendors and DigiCert’s forced 24-hour revocation of 83,000 certificates due to a domain validation bug served as a stark wake-up call. Trust is fragile, and operational rigor is non-negotiable.

Whether you are managing a sprawling internal PKI, evaluating a public Trust Service Provider, or securing a cloud-native microservices architecture, you need a modernized approach to auditing your trust anchors. This comprehensive Certificate Authority Security Assessment Checklist provides DevOps engineers, security professionals, and IT administrators with the actionable framework needed to secure PKI in 2025.

Why Your CA Security Posture Needs an Overhaul Now

Before diving into the checklist, it is crucial to understand the threat landscape and regulatory shifts driving these requirements.

1. The 90-Day Certificate Validity Push: Google's proposal to shrink the maximum validity of public TLS certificates from 398 days to 90 days means organizations will cycle through certificates four times faster. If your CA infrastructure and endpoint clients do not support fully automated Certificate Lifecycle Management (CLM) via protocols like ACME, you will experience catastrophic outages.
2. Post-Quantum Cryptography (PQC) Reality: In August 2024, NIST released the first three finalized post-quantum encryption standards (FIPS 203, 204, and 205). Threat actors are currently executing "harvest now, decrypt later" attacks. CAs must now be assessed on their cryptographic agility and readiness to support hybrid certificates.
3. Machine Identity Sprawl: Machine identities (containers, IoT devices, APIs) now outnumber human identities by staggering margins. Private CAs are scaling rapidly to secure DevOps pipelines, making them high-value targets for lateral movement and privilege escalation.
4. Private PKI Needs Public Rigor: Many organizations rely on internal Microsoft Active Directory Certificate Services (AD CS). Without strict auditing, these environments are notorious for misconfigurations (such as the infamous ESC1 through ESC8 vulnerabilities) that allow attackers to instantly escalate to Domain Admin privileges.

The 2025 Certificate Authority Security Assessment Checklist

Use this framework to evaluate your internal private CAs, cloud-based PKI-as-a-Service providers, and commercial public CAs.

1. Cryptographic & Architecture Security (The Foundation)

The core of any CA is its private key. If the root key is compromised, every certificate issued beneath it is invalidated, requiring a complete, organization-wide rebuild of trust.

• Offline Root CA: Is the Root CA completely air-gapped? It should be powered off, physically disconnected from any network, and stored in a highly secure physical location. It should only be brought online temporarily to sign Subordinate (Issuing) CAs or Certificate Revocation Lists (CRLs).
• Hardware Security Modules (HSMs): Are all CA private keys generated and stored within dedicated hardware? Ensure your HSMs are certified to at least FIPS 140-2 Level 3 (or FIPS 140-3). This applies to cloud environments as well; leverage services like AWS CloudHSM or Azure Key Vault Managed HSM.
• Algorithm Strength: Are you enforcing modern cryptographic standards? Ensure RSA keys are at least 3072-bit (preferably 4096-bit) and Elliptic Curve keys use at least NIST P-256 or P-384. Legacy algorithms like SHA-1 and MD5 must be strictly prohibited at the hardware level.
• PQC Readiness Roadmap: Does the CA architecture support cryptographic agility? You should have a documented timeline for migrating to NIST-approved post-quantum algorithms (like ML-KEM and ML-DSA) using hybrid certificate structures to maintain backward compatibility.

2. Logical & Operational Security (Defending the Issuing CA)

While the Root CA is offline, the Issuing CA is online and actively communicating with your network. It is the primary target for attackers.

• Strict Role-Based Access Control (RBAC): Are CA administrative roles strictly separated? You must enforce separation of duties among CA Administrators, Certificate Managers, Auditors, and Backup Operators. No single user should have the ability to configure the CA, approve a request, and clear the audit logs.
• Phishing-Resistant MFA: Is logical access to the CA infrastructure protected by FIDO2/WebAuthn hardware keys? Traditional SMS or push-notification MFA is no longer sufficient for Tier 0 infrastructure.
• Network Segmentation: Is the Issuing CA isolated in a highly restricted network zone? It should only accept traffic on specific ports (e.g., TCP 443 for enrollment APIs, TCP 80 for CRL/OCSP) from known, trusted subnets or API gateways.
• Active Directory CS Hardening: If using Microsoft AD CS, have you audited your certificate templates? Ensure you are actively scanning for ESC vulnerabilities (e.g., templates that allow client authentication while permitting the requester to specify a Subject Alternative Name, leading to domain takeover).
• Code Signing Strictness: As seen in the early 2024 AnyDesk breach, code-signing certificates are prime targets. Code-signing private keys must never leave the HSM, and signing operations must require multi-person approval pipelines.

3. Certificate Lifecycle & Automation (The 90-Day Reality)

With lifecycles shrinking, manual installation of certificates is a guaranteed path to an outage. Automation is now a baseline security requirement.

• Modern Automation Protocols: Does the CA natively support the Automated Certificate Management Environment (ACME) protocol, Simple Certificate Enrollment Protocol (SCEP), and Enrollment over Secure Transport (EST)?
• Agile Revocation Infrastructure: Are your Certificate Revocation Lists (CRLs) and Online Certificate Status Protocol (OCSP) responders highly available? In the event of a mass revocation (like the DigiCert incident), your OCSP responders must handle massive spikes in traffic without failing open or closed.
• Continuous Discovery and Inventory: Do you have comprehensive visibility into every certificate on your network? You cannot secure or rotate what you cannot see.

This is where a dedicated tracking solution becomes critical. Relying on spreadsheets to track 90-day certificates will inevitably result in expired certificates and application downtime. Implementing a robust monitoring platform like Expiring.at ensures you have real-time visibility into certificate lifecycles, automated alerts before expiration, and a centralized inventory of your entire TLS landscape, bridging the gap between issuance and operational monitoring.

4. Physical Security (For On-Premises PKI)

If you are hosting your own Root or Issuing CAs in a physical data center, the physical controls must be as rigorous as the logical ones.

• Tiered Access: Is the CA infrastructure housed in a secure rack within a Tier 3 or 4 data center?
• Multi-Factor Physical Access: Does reaching the physical server require biometric authentication, personalized badge access, and passage through a mantrap?
• M-of-N Control for Key Ceremonies: Are Root CA operations governed by M-of-N multi-person control? For example, accessing the HSM should require physical smart cards from 3 out of 5 designated keyholders, ensuring no single rogue administrator can sign a subordinate CA.
• Environmental Controls: Are there adequate fire suppression systems, redundant power supplies, and (for highly classified government or financial environments) Faraday cages to prevent electromagnetic interception?

5. Audit, Logging & Compliance

A CA that cannot prove its integrity is a CA that cannot be trusted.

• Immutable Logging: Are all CA activities—including certificate issuance, revocation requests, template modifications, and failed login attempts—forwarded to a centralized, immutable Security Information and Event Management (SIEM) system?
• Anomalous Behavior Alerting: Are alerts configured for