Identity-based access authenticates the user through a managed identity and issues access according to policy, often with short-lived credentials. File-based SSH access depends on possession of PEM or PPK files that act as long-lived secrets. The first approach improves control, revocation, and auditability. The second increases operational sprawl and the chance of unmanaged credential exposure.
Why Identity-Based SSH Access Is a Different Security Model
Identity-based access changes the trust anchor from a stored SSH file to a managed identity and a policy decision. That matters because cloud access then becomes something security teams can govern centrally, time-bound, and revoke without hunting down copies of a key file on laptops, build agents, or shared jump hosts. For instance, identity-based access is easier to align with OWASP Non-Human Identity Top 10, which focuses attention on the risks of unmanaged machine access and long-lived credentials.
File-based SSH access works differently: possession of a PEM or PPK file is effectively possession of the credential, so the operational model depends on protecting a secret file rather than asserting identity through policy. That increases the chance of uncontrolled duplication, stale access, and weak offboarding. The difference is not just convenience; it changes how access is granted, how fast it can be removed, and how confidently it can be audited. In practice, many teams discover the real cost of file-based SSH only after a key has been copied into a CI system or left behind during instance replacement.
How the Two Models Work in Practice
Identity-based SSH access typically starts with a central identity provider or cloud IAM policy that authorises a user, workload, or operator role for a bounded session. Access can be short-lived, tied to context, and logged as an identity event rather than as a static file use. This makes it easier to enforce least privilege, rotate trust quickly, and prove who accessed which instance and when. By contrast, file-based SSH access usually depends on a private key stored somewhere the operator can retrieve it, such as a workstation, vault export, configuration bundle, or automation pipeline. The key may still be encrypted, but the core control remains possession of the file.
- Identity-based access improves revocation because the permission can be removed centrally instead of waiting for every key copy to be found.
- File-based SSH is simple to start with, but it tends to spread across endpoints and scripts as soon as teams automate instance access.
- Identity-based access fits better with short-lived credentials and session auditing, while file-based access often leaves a longer forensic tail and more uncertain ownership.
- File-based access can still be valid in legacy environments, but it usually demands stronger key inventory and rotation discipline than teams expect.
NHIMG research shows why this distinction matters at scale: 88.5% of organisations say their non-human IAM practices lag behind or are only on par with human IAM, and 59.8% see value in dynamic ephemeral credentials. That gap is exactly where SSH key files become risky, because the operational convenience of a saved file can outlast the governance around it. For broader context on non-human identity lifecycle issues, the Ultimate Guide to NHIs is useful reading.
These controls tend to break down when instance access is embedded in automation, shared across teams, or handled through ad hoc break-glass processes because the boundary between authorised session and leaked credential becomes hard to observe.
Common Variations and Edge Cases
Tighter identity-based control often adds orchestration overhead, so teams need to balance revocation speed and auditability against integration effort in older platforms. Some cloud environments support identity federation cleanly, while others still require SSH keys for certain bastion patterns, vendor appliances, or cross-account administration. The practical question is not whether SSH keys exist at all, but whether they are treated as controlled exceptions or as the normal access path.
A common edge case is ephemeral infrastructure. If instances are frequently rebuilt, a static key file can survive long after the instance it originally protected has gone away, which weakens both traceability and offboarding. Another edge case is automation: a pipeline that uses file-based SSH may work reliably, but it also creates a high-value secret that often needs separate vaulting, distribution, and rotation controls. Where teams have not centralised that discipline, the file becomes the real identity. Guidance is evolving, but current best practice is to prefer policy-driven, time-bound access whenever the environment can support it, and to reserve file-based access for narrow compatibility cases rather than default operation.
Risk and Threat Considerations
File-based SSH access creates concentrated exposure because the private key is a reusable secret that can be copied, cached, or embedded into automation. If that file is stolen, the attacker gains the same access path as the legitimate user until the key is rotated or removed, and detection is often weaker because the event may look like ordinary SSH use.
Failure mechanism: The risk materialises when long-lived keys are distributed beyond their intended holder, stored in code or build systems, or left active after role changes. An adversary who obtains the file can authenticate directly, bypass central policy checks that would otherwise govern session start, duration, and revocation.
Impact: The result can be persistent instance access, lateral movement across similarly configured hosts, and delayed incident containment because revoking the credential requires finding every copy and every dependent workflow.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST CSF 2.0 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-01 — Secrets and Credential Management | SSH key files are long-lived machine credentials that must be governed. |
| NHI-03 — Authorization and Least Privilege | Identity-based SSH relies on policy-bound access rather than file possession. | |
| Recommendation — Inventory, rotate, and revoke SSH private keys as managed non-human credentials. Grant instance access through least-privilege policies and remove excess trust paths. | ||
| NIST CSF 2.0 | PR.AC-1 — Identity Management, Authentication, and Access Control | The question contrasts managed identity access with static secret-based access. |
| Recommendation — Use managed identity controls to authenticate users and workloads before granting access. | ||
| CIS Controls v8 | 6.3 — Access Control Management | SSH access differences directly affect account and key lifecycle control. |
| 5.3 — Secure Service Account Management | Cloud instance access often extends to automated workloads and service identities. | |
| Recommendation — Centralise access approvals and promptly remove obsolete SSH access paths. Replace shared SSH files with governed identities for automated instance access. | ||
Practitioner Guidance
What to prioritise: Treat the access model choice as a control decision, not a tooling preference. If the environment can support identity-based SSH, prioritise it for human operators and for any automation that does not truly require a long-lived file.
What to verify: Confirm whether any existing PEM or PPK files are still being used by CI jobs, break-glass accounts, or shared admin paths. If they are, verify ownership, rotation cadence, and offboarding coverage before assuming the access path is controlled.
Practitioner takeaway: The meaningful difference is not SSH syntax; it is whether access is governed as an identity with bounded authority or as a portable secret that must be hunted down after the fact.
Related resources from NHI Mgmt Group
- What is the difference between manual SSH key management and centralized identity-based SSH access?
- What is the difference between OT network segmentation and identity-based access control?
- What is the difference between workload identity and secret-based access?
- What is the difference between Kubernetes network policy and identity-based access control?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 10, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
