Zero Trust and PKI define identity verification across digital systems

At a glance

What this is: This is a Zero Trust and PKI explainer that says continuous verification is the basis of digital trust across users, devices, services, and documents.

Why it matters: It matters because IAM, NHI, and access governance teams need identity controls that verify every connection, not just initial authentication, across human and machine programmes.

👉 Read DigiCert's overview of Zero Trust, PKI, and digital trust

Context

Zero Trust is an identity and access model that assumes no user, device, service, or document should be trusted by default. The core issue is not simply perimeter collapse, but the need to verify every connection every time, especially as access paths now span human identity, service accounts, workloads, and digital documents.

That makes PKI relevant to identity governance, not just transport security. Certificates, public-private keys, MFA, and SSO become the mechanisms that establish and re-establish trust at runtime. For practitioners, the real question is whether verification is embedded across the full access lifecycle or only at the first login.

Key questions

Q: How should security teams implement Zero Trust for both human and machine identities?

A: Security teams should use Zero Trust as an identity verification model, not just a network segmentation model. For humans, that means MFA, SSO, and strong authentication. For machines and services, it means certificate-backed identity, lifecycle control, and revocation discipline so trust can be re-established at every connection.

Q: Why do service and workload identities need PKI in Zero Trust environments?

A: Service and workload identities often need to authenticate without a human present, which makes passwords and one-time logins a poor fit. PKI gives those identities durable cryptographic proof, while also supporting encryption and integrity. That makes it easier to verify what is connecting before access is granted.

Q: What breaks when certificate lifecycle management is weak?

A: Weak certificate lifecycle management creates stale trust, expired access, and revocation gaps. In Zero Trust designs, that means systems may continue accepting identity proof that no longer reflects the real owner, purpose, or risk level. The result is hidden exposure that looks compliant until it is tested.

Q: Who is accountable when a trusted certificate is misused?

A: Accountability should sit with the team that owns certificate issuance, lifecycle governance, and identity policy for the affected environment. Zero Trust depends on continuous verification, so ownership must extend beyond deployment to renewal, revocation, and monitoring. NIST Cybersecurity Framework 2.0 can help map those governance responsibilities.

Technical breakdown

How PKI anchors Zero Trust verification

Public key infrastructure binds a cryptographic key pair to an identity through certificates, allowing systems to authenticate who or what is connecting. In Zero Trust designs, that identity proof is not a one-time event. It supports repeated verification across applications, services, devices, and documents, which reduces reliance on network location or implicit trust. PKI also provides encryption and integrity, so the same trust primitive can protect both identity and data. The architectural point is that Zero Trust needs a durable proof of identity, not just a password check or a one-off session grant.

Practical implication: map high-value connections to certificate-backed identity proof rather than relying on perimeter trust or static session assumptions.

Why MFA and SSO still need certificate trust

MFA and SSO improve authentication flow, but they do not by themselves prove the cryptographic identity of the endpoint or workload. In practice, Zero Trust works best when PKI complements those controls, especially where users move between devices, apps, and remote access paths. That combination helps reduce impersonation risk and prevents access decisions from depending solely on a successful interactive login. For machine and service identities, certificate-backed authentication is often the more durable trust anchor because it survives the limitations of human-centric login methods.

Practical implication: do not treat MFA and SSO as substitutes for certificate-based identity assurance in machine-to-machine or high-trust access paths.

Why certificate lifecycle management is a Zero Trust control

Zero Trust fails if certificates cannot be issued, monitored, rotated, and revoked with the same discipline applied to other credentials. The article points to trust lifecycle management as a way to centralize visibility and control, which matters because PKI only strengthens trust when certificate states remain current. Expired, over-permitted, or unmanaged certificates create blind spots that undermine the verification model. In other words, Zero Trust is not only about authenticating identities, but about maintaining trustworthy identity artefacts across their full lifecycle.

Practical implication: treat certificate lifecycle management as a core Zero Trust control and include it in entitlement, renewal, and revocation workflows.

Threat narrative

Attacker objective: The objective is to turn a trusted-looking connection into unauthorized access to internal applications, services, or protected data.

1. Entry occurs when an attacker or unauthorised actor can present a connection that appears trusted enough to reach the environment. In Zero Trust terms, the objective is to get past the first identity check or exploit an overtrusted path.
2. Escalation follows when access decisions rely on static trust, weak verification, or unmanaged certificates that outlive their intended use. That allows the actor to move from initial access to broader identity and service reach.
3. Impact occurs when the trusted connection is used to access apps, services, data, or documents that should have required fresh verification. The result is identity-driven exposure rather than perimeter-based containment.

Breaches seen in the wild

• Cisco DevHub NHI breach — IntelBroker exploited exposed Cisco credentials, API tokens and keys in DevHub.
• DeepSeek breach — DeepSeek breach exposed 1M+ log lines and sensitive secret keys.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

Zero Trust is only as strong as the identity proof behind each connection. The article is correct that perimeter trust has failed as a security model, but the deeper issue is that Zero Trust depends on trustworthy identity artefacts at runtime. If the certificate, token, or session assertion is stale or unmanaged, continuous verification becomes a slogan rather than a control. Practitioners should treat identity proof as the operational core of Zero Trust, not a supporting detail.

PKI is the trust layer that lets Zero Trust extend beyond human login events. Human IAM controls such as MFA and SSO are necessary, but they do not solve service, device, and document verification on their own. That is why certificate-backed identity is central to workload and machine access, especially where access must be re-validated across distributed systems. The implication for programmes is that IAM and NHI governance cannot stay separate if continuous verification is the goal.

Certificate lifecycle drift creates identity trust debt. Certificates that are issued once but not continuously monitored, rotated, and revoked create a hidden backlog of trust assumptions that no longer match reality. That backlog becomes attack surface because a valid-looking credential can remain accepted long after ownership, purpose, or risk has changed. This is the same structural problem NHIMG sees across machine identity governance: trust artefacts persist longer than the business context that justified them.

Identity governance must move from access grant logic to verification durability. The article frames digital trust as something rebuilt at every connection, which is the right direction for security architecture. The field-level implication is that governance cannot stop at provisioning or login assurance. Zero Trust programmes need lifecycle discipline for certificates, service identities, and user authentication paths so that verification remains meaningful after initial issuance.

Named concept: verification durability. In Zero Trust environments, the real control objective is not merely proving identity once, but sustaining trustworthy proof across the lifetime of the connection. That matters because modern access paths span users, services, devices, and documents, each with different expiry and revocation behavior. Practitioners should design governance around how long identity proof remains trustworthy, not only whether it was valid at first contact.

From our research:

• 90% of IT leaders say properly managing NHIs is essential for a successful zero-trust implementation, according to Ultimate Guide to NHIs.
• Only 5.7% of organisations have full visibility into their service accounts, which shows how often identity assurance breaks before Zero Trust can work as intended.
• For a deeper control model, see Ultimate Guide to NHIs , Standards for the standards and control families that anchor verification and lifecycle governance.

What this signals

Verification durability: the next Zero Trust maturity question is not whether access is protected at login, but whether identity proof stays trustworthy across renewal, rotation, and revocation. Teams that cannot trace that lifecycle will struggle to prove they are operating beyond perimeter trust.

With 96% of organisations storing secrets outside secrets managers in vulnerable locations including code, config files, and CI/CD tools, according to the State of Secrets in AppSec, the verification problem extends far beyond human logins and into machine identity hygiene.

Zero Trust programmes that separate human IAM from workload and certificate governance will keep running into the same gap. The practical next step is to align policy, lifecycle, and runtime verification so that trust is continuously re-earned rather than assumed after issuance.

For practitioners

• Map trust points to cryptographic identity proof Identify every place where users, devices, services, and documents are accepted on the basis of a trust decision. Replace implicit network trust with certificate-backed verification for the highest-risk connections.
• Align MFA and SSO with workload identity controls Use MFA and SSO for human access, but pair them with certificate-based identity for workloads, services, and remote systems that must authenticate without human interaction.
• Put certificate lifecycle under governance Track issuance, renewal, rotation, expiration, and revocation as governed identity events. Treat unmanaged certificates as standing trust debt, not as routine infrastructure noise.

Key takeaways

• Zero Trust is an identity model first and a perimeter model only second.
• PKI, MFA, and SSO work together when certificate lifecycle governance keeps identity proof current.
• The main operational risk is trust artefacts that outlive the context that made them valid.

Key terms

• Zero Trust: A security model that assumes no user, device, service, or connection is trusted by default. Access is granted only after explicit verification and must continue to be re-evaluated as context changes, making identity assurance a continuous control rather than a one-time gate.
• Public Key Infrastructure: A system for binding cryptographic keys to identities through certificates. In identity programmes, PKI provides authentication, encryption, and integrity for users, devices, services, and documents, which makes it a core trust mechanism for Zero Trust and machine identity governance.
• Certificate Lifecycle Management: The governed process of issuing, renewing, rotating, monitoring, and revoking certificates. It matters because a certificate only supports trustworthy access while its status matches reality, and stale or unmanaged certificates become persistent identity risk across the environment.
• Digital Trust: The confidence that a system can verify who or what is connecting and can protect the integrity of that interaction. It is stronger when identity proof is cryptographic, continuously checked, and tied to lifecycle controls instead of implicit network assumptions.

Deepen your knowledge

NHI Foundation Level course, the industry's only accredited NHI security programme, covers NHI governance, machine identity security, and identity lifecycle management. If you are responsible for identity security strategy or access governance in your organisation, it is worth exploring.

This post draws on content published by DigiCert: Zero Trust and PKI as the foundation of digital trust. Read the original.