In short: PKI as a service (PKIaaS) delivers a certificate authority as a subscription, so you consume trust instead of building it. It sits on a spectrum with on-prem PKI, cloud PKI, and managed PKI, and the right choice depends on your control, compliance, and staffing needs rather than on any single "best" model.
Every organisation that issues certificates faces the same question: run the certificate authority yourself, or have someone run it for you. The answer used to be simple because on-prem was the only real option. Today there are several deployment models, and the labels overlap in confusing ways.
This guide compares the main options and, in particular, explains where PKI as a service fits. The goal is not to crown a winner but to match each model to the organisations it actually suits.
What PKI as a service (PKIaaS) means
PKIaaS delivers a full certificate authority as an operated, subscription service. The provider runs the CA software, protects the root and issuing keys in certified HSMs, handles availability and audits, and exposes issuance through APIs and standard protocols such as ACME, EST, and SCEP.
Crucially, PKIaaS is about who operates the trust, not merely where it runs. You keep your certificate policy and control issuance, while the heavy operational burden, key ceremonies, hardware, patching, and resilience, sits with the provider.
The four deployment models compared
It helps to see the options as a spectrum from full control to full delegation.
- On-prem PKI: you own the hardware, software, and staff. Maximum control and data locality, but also maximum operational load and single-points-of-failure risk.
- Cloud PKI: the same CA software runs in cloud infrastructure. You gain elasticity but still carry design and day-to-day operations yourself.
- Managed PKI: an expert team operates your CA, on-prem or cloud, under your policy, sharing responsibility for uptime and audits.
- PKIaaS: a multi-tenant or dedicated service you subscribe to, with the provider owning the platform and you owning policy and issuance.
The models are not mutually exclusive. Many organisations combine, for example, an on-prem root with hosted issuing CAs for specific use cases.
How to choose the right model
Use these questions to narrow the field quickly.
- Control and sovereignty: Do regulations or internal policy require keys and data to stay in a specific jurisdiction or on your own hardware?
- In-house expertise: Do you have staff who can run key ceremonies, HSMs, and CRL/OCSP reliably around the clock?
- Scale and volume: Are you issuing a few hundred certificates or millions across workloads and devices?
- Speed to value: How quickly must you stand up trusted issuance for a new project?
- Compliance load: Who will carry the evidence burden for NIS2, DORA, and audit requirements?
Why PKIaaS is gaining ground
Two pressures push organisations toward managed and hosted PKI. First, certificate volumes are exploding as machine identities outnumber human ones. Second, certificate lifetimes are shrinking: the CA/Browser Forum decided in 2025 to reduce the maximum lifetime of public TLS certificates in stages toward 47 days by 2029, which makes manual renewal untenable.
PKIaaS answers both by pairing an operated, resilient CA with automation for issuance and renewal. Teams get modern, short-lived certificates and audit-ready operations without hiring a dedicated PKI team.
Avoiding the hidden costs of DIY PKI
Running your own CA looks cheaper until you count the full lifecycle: hardware refreshes, HSM maintenance, high-availability design, staff on call, and the reputational cost of a single expired certificate taking down a service. On-prem PKI remains the right call for some highly sovereign workloads, but for many others the total cost favours a managed or PKIaaS model.
Whatever the model, the deciding factor is operational discipline. A well-run cloud PKI beats a neglected on-prem one every time.
How CRYPTAS helps
CRYPTAS operates PKI across the full spectrum, from managed PKI to hybrid designs with an on-prem root, so you can match control, sovereignty, and cost to each use case without compromising on security or audit readiness.
Not sure which PKI deployment model fits your organisation?
Explore: Enterprise PKI · Managed Services · Certificate Lifecycle Management