Shared device keys make revocation and containment far harder than in systems with unique identities. Industrial environments often have long device lifecycles, so one compromised key can remain useful for years unless the organisation has a clear replacement and rotation strategy. That creates persistent exposure, especially where devices cannot be patched quickly.
Why This Matters for Security Teams
Shared device keys in OT collapse many devices into one security decision. That is efficient for provisioning, but it creates a single compromise domain: if one key leaks from a field device, gateway, or maintenance workflow, every system using that key can be impersonated until the key is replaced everywhere. That is especially dangerous in plants where devices are difficult to inventory and even harder to take offline.
Operational teams often underestimate how quickly shared secrets spread across vendors, remote support paths, and integrator handoffs. The result is a control weakness that looks small on paper but can persist across years of uptime. NHI Management Group’s Ultimate Guide to NHIs — Key Challenges and Risks notes that 71% of NHIs are not rotated within recommended time frames, which is a useful proxy for why shared keys linger so long in real environments. For broader governance context, the NIST Cybersecurity Framework 2.0 remains a useful baseline for inventory, protection, and recovery planning.
In practice, many security teams discover shared-key exposure only after a maintenance account, historian connector, or vendor remote-access path has already been abused.
How It Works in Practice
The core issue is that a shared key is not an identity in the operational sense. It is a reusable credential that lets multiple assets present the same trust signal. In OT, that trust signal often exists because of legacy design, constrained hardware, or the need to onboard large device fleets quickly. But once the same key is reused across many endpoints, security teams lose the ability to answer basic questions such as which device used the key, when it was last seen, or whether it should still be trusted.
Effective mitigation starts with moving from shared keys toward unique device identities and segmented trust. Current guidance suggests pairing this with centralized secret lifecycle management, asset inventory, and deterministic replacement procedures so that a compromise can be contained to one device or one site rather than the entire estate. For examples of how weak identity governance drives real-world exposure, see Top 10 NHI Issues and the 2024 ESG Report: Managing Non-Human Identities, which reports that 72% of organisations have experienced or suspect a breach of non-human identities.
- Assign a unique identity per device, cell, or gateway where the platform allows it.
- Store credentials in a controlled system of record, not in vendor manuals, scripts, or shared field notes.
- Enforce rotation and revocation workflows that can be executed without a full outage.
- Limit the blast radius with network segmentation and strict device-to-service allowlists.
- Validate that replacement procedures work before a key is actually lost or exposed.
These controls tend to break down in brownfield plants with fragile uptime dependencies, opaque vendor support arrangements, and equipment that cannot support per-device certificate or token issuance.
Common Variations and Edge Cases
Tighter key control often increases operational overhead, requiring organisations to balance resilience against maintenance complexity. That tradeoff is most visible in older OT environments where a full identity redesign is not immediately realistic, so teams need an interim model rather than a perfect one.
One common exception is vendor-managed equipment that only supports a fleet-wide shared credential. In those cases, best practice is evolving, but current guidance suggests compensating with tighter segmentation, shorter validity windows where possible, and rigorous change control. Another edge case is emergency response access: plant teams sometimes preserve a shared key for downtime recovery, then never remove it. That temporary exception becomes a standing risk unless there is an explicit expiry and review cycle.
The Schneider Electric credentials breach illustrates how credential exposure can expand beyond the intended system boundary, while the Ultimate Guide to NHIs — Why NHI Security Matters Now reinforces why slow rotation and weak visibility are especially dangerous. In mixed IT/OT estates, shared keys are also harder to govern because access often crosses engineering, operations, and third-party support boundaries at the same time.
The practical rule is simple: if one credential can authenticate more than one device, then compromise containment depends on process discipline instead of technical separation.
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 NIST Zero Trust (SP 800-207) set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-03 | Shared keys create rotation and revocation risk across many devices. |
| NIST CSF 2.0 | PR.AC-1 | Identity and credential management underpins access control for OT devices. |
| NIST Zero Trust (SP 800-207) | PR.AC-4 | Zero Trust reduces blast radius when device credentials are compromised. |
Replace shared OT keys with unique identities and enforce rapid rotation when compromise is suspected.
Related resources from NHI Mgmt Group
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Reviewed and updated by the NHIMG editorial team on June 23, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
