The Ultimate Certificate Authority (CA) Security Assessment Checklist for 2025
The landscape of Public Key Infrastructure (PKI) and Certificate Authorities (CAs) is experiencing a seismic shift. If you are still treating your internal CA security assessment as a static, annual checkbox exercise, your infrastructure is already falling behind.
In 2024, the industry witnessed unprecedented disruptions. Google Chrome and Mozilla made the historic decision to distrust certificates issued by Entrust following repeated compliance failures and delayed incident reporting. Shortly after, a logic flaw in DigiCert's domain validation process forced the mass revocation of approximately 83,000 certificates within a 24-hour window.
These incidents prove that no CA is "too big to fail." Whether you are managing an internal Microsoft ADCS instance, a cloud-native HashiCorp Vault PKI, or consuming public trust, your CA infrastructure must be resilient, automated, and relentlessly audited.
Coupled with Google’s "Moving Forward, Together" initiative—which aims to reduce maximum public TLS certificate validity from 398 days to just 90 days—and the impending reality of Post-Quantum Cryptography (PQC), manual certificate management is now mathematically impossible.
To survive this new era, DevOps engineers, security professionals, and IT administrators must adopt a modernized CA assessment framework. Here is the comprehensive, four-pillar CA Security Assessment Checklist for 2025.
Pillar 1: Cryptographic & Key Management Security
The foundational trust of any CA relies entirely on how its private keys are generated, stored, and utilized. If a root key is compromised, every certificate issued beneath it is instantly invalidated.
Hardware Security Modules (HSMs)
Never store CA private keys on a standard server filesystem.
* Check: Are your Root and Issuing CA keys generated and stored within an HSM certified to FIPS 140-2/3 Level 3 or Common Criteria EAL 4+?
* Check: Are you utilizing a verified True Random Number Generator (TRNG) for key entropy?
Key Generation Ceremonies
A compromised key generation process ruins the CA before it even begins operating.
* Check: Do you enforce a documented, video-recorded Key Generation Ceremony?
* Check: Is M-of-N multi-person control enforced? For example, requiring 3 out of 5 designated key custodians to present physical smart cards to activate the Root CA.
Crypto-Agility and Post-Quantum Readiness
In August 2024, NIST finalized the first three Post-Quantum Cryptography standards (FIPS 203, 204, and 205). Your CA must support modern algorithms today and have a roadmap for tomorrow.
* Check: Does your CA natively support modern Elliptic Curve algorithms (ECDSA P-384, Ed25519)?
* Check: Can your infrastructure issue hybrid certificates (combining traditional RSA/ECC with quantum-resistant algorithms like ML-KEM)?
You can actively audit your current internal certificates to ensure they are moving away from legacy RSA-2048 using openssl:
# Check the public key algorithm and size of a specific certificate
openssl x509 -in internal-service.crt -text -noout | grep -A 2 "Public Key Algorithm"
# Expected output for a modernized certificate:
# Public Key Algorithm: id-ecPublicKey
# Public-Key: (384 bit)
# NIST CURVE: P-384
Pillar 2: Logical & Network Security
Once your keys are secure, the systems interacting with them must be locked down using Zero Trust principles.
The Air-Gapped Root
- Check: Is your Root CA completely offline? It should be physically disconnected from all networks, powered off, and stored in a secure safe, only brought online to sign Subordinate/Issuing CAs or CRLs.
Network Segmentation & Access Control
Issuing CAs must be online, making them prime targets for lateral movement during a network breach.
* Check: Are Issuing CAs isolated in highly restricted DMZs with strict egress/ingress firewall rules? Only necessary protocols (CMP, EST, SCEP, ACME) should be permitted.
* Check: Is strict Role-Based Access Control (RBAC) enforced?
* Check: Are all CA administrators required to authenticate using phishing-resistant MFA, such as FIDO2/WebAuthn hardware security keys?
If you are using HashiCorp Vault as your internal CA, your logical security relies heavily on strict HCL policies. A proper assessment should verify that applications only have access to the specific PKI roles they need:
# Example Vault Policy: Restrict web servers to only issue certs for their specific domain
path "pki_int/issue/web-servers" {
capabilities = ["create", "update"]
# Ensure the requested common_name matches the allowed pattern
allowed_parameters = {
"common_name" = ["*.internal.example.com"]
"ttl" = ["720h"] # Max 30 days
}
}
Pillar 3: Physical Security & Infrastructure
Cloud-managed PKI solutions like AWS Private CA or Google CAS offload much of this burden, but if you host your own HSMs or offline roots, physical security is paramount.
- Check: Is the CA hosted in a Tier 3 or Tier 4 data center?
- Check: Are physical access controls multi-factor? The industry standard requires at least three factors (e.g., RFID Badge + Biometric Scan + PIN) to access the CA server cage.
- Check: Are servers and HSMs stored in tamper-evident racks?
- Check: Is there 24/7 CCTV monitoring covering the CA hardware, with footage immutably retained for a minimum of 90 days?
Pillar 4: Operational Management & Automation
With machine identities now outnumbering human identities by 45:1, and the 90-day public certificate lifespan fast approaching, automation is no longer optional. A CA that cannot automate issuance and revocation is a liability.
Revocation Infrastructure
The DigiCert incident highlighted the critical need for rapid, reliable revocation.
* Check: Are your Certificate Revocation Lists (CRLs) and Online Certificate Status Protocol (OCSP) responders highly available (HA)?
* Check: Can your OCSP responders withstand a volumetric DDoS attack?
Automated Certificate Management Environment (ACME)
To survive the 90-day lifespan rule, your internal CA must support the same automation protocols used by public CAs like Let's Encrypt.
* Check: Does your CA support ACMEv2 (RFC 8555)?
If you are running an internal CA using tools like Smallstep (step-ca), you can easily assess its automation readiness by configuring standard ACME clients like certbot to interact with it:
# Requesting an internal certificate automatically using an internal ACME CA
REQUESTS_CA_BUNDLE=$(step path)/certs/root_ca.crt \
certbot certonly -n --standalone -d internal-api.example.com \
--server https://ca.internal.example.com/acme/acme/directory
Immutable Logging & Disaster Recovery
- Check: Are all CA activities (issuance, revocation, policy changes) forwarded in real-time to an immutable SIEM (Security Information and Event Management) system?
- Check: Do you have a documented and actively tested Disaster Recovery (DR) plan? You must define a strict Recovery Time Objective (RTO) and Recovery Point Objective (RPO) for your Issuing CA.
Compliance and Regulatory Mapping
A robust CA assessment doesn't exist in a vacuum; it must map to established industry frameworks. When auditing your infrastructure, benchmark against the following:
- CA/Browser (CAB) Forum Baseline Requirements: This is the absolute gold standard for public trust. Even if you run a private CA, you should assess your certificate profiles against these rules. You can use open-source tools like ZLint to programmatically check your issued certificates for CAB Forum compliance.
- NIS2 Directive: Effective in Europe as of late 2024, NIS2 requires critical infrastructure entities to implement strict cryptographic controls and incident reporting. Your internal CA assessments are a major component of NIS2 compliance.
- DORA (Digital Operational Resilience Act): Coming into force in 2025, financial institutions must prove the resilience of their cryptographic infrastructure, including stringent audits of third-party CA providers.
The Automation Paradox: Why You Still Need Out-of-Band Monitoring
There is a dangerous misconception that implementing ACME and automated certificate lifecycle management (CLM) solves all PKI problems. In reality, automation introduces new failure modes.
Cron jobs fail. ACME endpoints get blocked by aggressive firewall rules. DNS validation records get accidentally deleted. When automated renewal fails silently, you end up with an unexpected, catastrophic outage.
This is where out-of-band monitoring becomes a critical requirement in your CA assessment. You cannot rely solely on the system issuing the certificates to tell you if the certificates are validly deployed on the endpoints.
To bridge this gap, implement independent monitoring using Expiring.at. Expiring.at acts as an external source of truth, continuously scanning your public-facing and internal endpoints to verify that your automated CA is actually doing its job.
By integrating Expiring.at into your operational lifecycle, you gain:
* Defense-in-Depth: If your internal automated renewal scripts fail, Expiring.at will catch the expiring certificate before it causes an outage.
* Actionable Alerts: Route expiration warnings directly to the teams that need them via Slack, Email, or custom Webhooks.
* Endpoint Validation: Ensure that the new certificate wasn't just issued by the CA, but successfully bound to the web server or load balancer.
Conclusion: Next Steps for 2025
The era of "set it and forget it" PKI is officially over. The Entrust and DigiCert incidents of 2024 have proven that operational transparency, rapid revocation capabilities, and strict adherence to security checklists are non-negotiable for modern infrastructure.
To prepare for 2025, take the following immediate actions:
1. Audit your algorithms: Run an inventory of