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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Before adopting a new TLS certificate authority (CA), decide whether it will issue publicly trusted certificates or serve an internal trust domain, identify every client that must accept its certificates, and verify the CA’s policies, audit evidence, hierarchy, and operational controls. Then test complete certificate paths against the actual client software and versions you support. A DNS CAA record can limit which CAs are authorized to issue for a domain, but it cannot prove that a certificate is valid or trusted.
First define what kind of trust you are adding
Record the intended use before comparing providers: public Internet-facing server certificates, internal-only services, mutual TLS, a constrained enterprise trust domain, or a combination. Public trust and private enterprise PKI have different trust boundaries and evidence requirements.
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| Question | Publicly trusted CA | Private enterprise CA |
|---|---|---|
| Who must trust it? | Clients whose application-software suppliers include the relevant root in their trust programs. | Only the clients and systems where your organization installs or configures the private trust anchor. |
| Which requirements apply? | Applicable root-store policies and current CA/Browser Forum TLS Baseline Requirements, among other program-specific obligations. | Your organization’s security, governance, deployment, and lifecycle requirements. Public TLS requirements do not automatically define the complete control framework for internal-only PKI. |
| What can you assume about acceptance? | Acceptance by one root-store program does not establish acceptance by every program or client. | Acceptance depends on how roots are installed, updated, constrained, and removed across managed clients. |
The CA/Browser Forum says its TLS Baseline Requirements concern certificates for Internet-accessible TLS servers and exclude internal-only enterprise PKI where the root is not distributed by an application-software supplier. For public certificates, identify each relevant root-store program rather than treating “publicly trusted” as a universal status.
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A certificate chain typically connects a leaf certificate to one or more subordinate CAs and then to a trust anchor. The trust anchor is selected by the relying client; a technically well-formed chain is not automatically trusted everywhere. RFC 5280 defines path validation in relation to a trust anchor, while TLS 1.3 leaves detailed certificate validation to other specifications and recommends careful trust-anchor selection.
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- Draw the proposed path from trust anchor through every subordinate CA to the leaf certificates you expect to use.
- Identify whether adoption adds a root, adds an intermediate beneath an existing trusted root, or introduces a private trust anchor. These options have different reach and potential blast radius.
- Review CA certificate constraints, permitted names and purposes, and the certificate profiles the CA will issue.
- Check that the intended path is compatible with clients’ path-building behavior; do not assume every client constructs a chain the same way.
Request evidence of governance and operating controls
Ask for the current Certificate Policy (CP) and Certification Practice Statement (CPS), plus their revision history. They should make validation, issuance, revocation, incident notification, and subordinate-CA practices understandable enough to assess against your requirements.
Audit and policy evidence
- Obtain independent audit statements applicable to the specific CA certificates and time periods under review. Confirm the criteria, scope, exceptions, and any supplemental reports; a logo or brief assurance statement is not a substitute.
- For a public CA, map the evidence to each target root-store policy and the current CA/Browser Forum requirements. These policies are program-specific and can change.
- Mozilla’s Root Store Policy is one example of a program requiring applicable baseline compliance and audit evidence; it does not establish acceptance by other root programs.
- Mozilla’s June 2026 policy update describes a Detailed Controls Report intended to improve visibility into controls, testing, and operating effectiveness. Assess the evidence that applies to the CA and period you are evaluating.
Incidents, accountability, and third parties
- Review disclosed incidents and the CA’s response, including root-cause analysis, remediation milestones, and evidence that corrective actions were tested.
- Confirm ownership, operational control, relevant jurisdictions, escalation contacts, and whether third parties operate any part of the hierarchy.
- Check issuance and revocation operations, including availability and response commitments that matter to your architecture. Do not assume that all client platforms check revocation in the same way.
Examine CA hierarchy and private-key protection
Assurance should match the CA’s role. Review how CA keys are generated, held, accessed, backed up, recovered, and protected from compromise, using applicable policy requirements and audit evidence rather than a vendor statement alone.
- Ask for evidence covering key custody, access controls, operational separation, ceremony records, backup and recovery, and change control.
- Understand the controls over subordinate CAs, including who can authorize them and what issuance constraints apply.
- Confirm the CA has a documented compromise response and know how it would affect certificates and trust paths in your environment.
- Set acceptance criteria for algorithms and key sizes based on current applicable policy and the cryptographic capabilities of your supported clients. RFC 8446 recommends enforcing minimum and maximum key sizes.
Exact requirements vary by trust program and CA role. Compare evidence against the requirements that actually apply to the proposed chain.
Check the clients that must accept the certificates
Make a client inventory before rollout. A browser, operating system, language runtime, appliance, container, mobile client, and long-lived device may rely on different trust stores or use different versions of them.
- For each client family, record supported versions and whether trust comes from a system store, application-specific store, or explicitly configured private store.
- For public certificates, confirm which root-store programs and versions cover the clients in scope. For private PKI, document how trust anchors are distributed, updated, constrained, and removed on managed clients.
- Check certificate transparency and audit requirements that apply to the relevant public trust program. Do not assume a single CT rule or enforcement behavior applies to every client or to private PKI.
- Confirm the certificate profile and algorithms are compatible with the clients and services that will use them.
Test full certificate paths and failure behavior
Use the real client software and supported versions in scope, not just a single command-line validator. RFC 5280 provides the general path-validation framework, but client trust stores and implementation behavior determine whether a path works in practice.
- Serve a representative certificate and complete chain. Ensure required intermediates are delivered correctly and the path can be built by each target client.
- Verify certificate identity and constraints. Check hostname matching, issuer sequencing, validity dates, path constraints, intended certificate purposes, and algorithm and key-strength acceptance.
- Exercise negative cases. Test expired and not-yet-valid certificates, missing or incorrect intermediates, an unapproved issuer, and a revoked test certificate where the platform supports meaningful revocation testing.
- Observe platform-specific results. Record handshake outcomes and certificate errors across the actual client population. Revocation handling and trust-store behavior can differ by client and platform.
- Pilot and roll back safely. Stage trust-store or configuration changes, monitor failures, and expand only after the intended clients behave as expected. Keep a rollback plan for removing the new trust path.
Use CAA for issuance authorization, not certificate validation
DNS Certification Authority Authorization (CAA) records tell certificate issuers which CAs are authorized to issue for a domain. Under RFC 8659, compliance with a published CAA record is necessary but not sufficient for issuance. The RFC also states: “Relying Parties MUST NOT use CAA records as part of certificate validation.” Use CAA to reduce unauthorized-issuance risk; do not treat its presence as proof that an observed certificate was correctly issued, valid, or trusted by a client.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Compare candidate CAs against the same criteria
When evaluating multiple candidates, use one scorecard and require evidence for each dimension rather than relying on a general reputation claim.
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- Trust-store coverage for the actual client population.
- Audit scope, currency, exceptions, and remediation quality.
- Hierarchy design and subordinate-CA constraints.
- Private-key custody and operational controls.
- Certificate profiles, algorithms, and path compatibility.
- Issuance automation, renewal, revocation, and incident response.
- Transparency and disclosure practices.
- Exit cost, migration support, and the ability to remove trust cleanly.
Standards such as RFC 5280 and RFC 8446 provide stable foundations, but root-store policies and CA/Browser Forum requirements change. Check the applicable policies and requirements again at the time of an actual adoption decision.
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