How to Evaluate Tenant-Scoped KMS Key Policies on Shared GPU Hosts

Consider this evaluation scenario: two workloads share a Supermicro HGX B300 host. Each writes encrypted checkpoints using a different KMS key alias. The architecture diagram looks tenant-scoped. But both workloads reach KMS through one host agent whose identity can decrypt with either key.

When the evaluator submits Tenant B’s encrypted checkpoint through Tenant A’s job, the agent decrypts it. Separate aliases existed; separate authorization did not.

For founders comparing cloud services with on-prem GPU pods, that is the evaluation target: whether every path to key use preserves a tenant boundary, including shared services and administrative exceptions.

1. Define scope beyond a tenant-shaped alias

“Tenant-scoped” should mean that a tenant’s authorized workload identities can perform specified operations against its designated keys—and cannot use another tenant’s keys through direct calls or intermediaries.

On a multi-workload host, first define the tenant: a customer, project, enclave, or workload security domain. Then request a mapping of:

• Tenant identifier and authenticated workload identities.
• Canonical key IDs and any mutable aliases pointing to them.
• Key policies, identity policies, grants, and relevant resource conditions.
• Services that encrypt, decrypt, wrap, or unwrap data keys.

An alias is a convenient name, not proof of isolation. Ask who can retarget it and whether authorization evaluates the underlying key, the alias, or both. Those semantics vary by KMS.

Prefer distinct key resources for distinct authorization domains. If multiple tenants share one key, require an explicit explanation of how every access path enforces tenant restrictions; names and metadata alone do not establish them.

2. Separate key administration from data-plane use

Build a permission matrix with separate rows for policy editing, alias changes, grant creation, rotation, disabling, deletion, encryption, and decryption.

A key administrator should not automatically receive routine decrypt permission. A workload identity should not edit its own policy or create an unrestricted grant. Also examine escalation: an administrator who cannot decrypt today may still be able to modify policy and authorize itself tomorrow.

For sensitive changes, evaluate independent approval, constrained administrative roles, and attributable change records. Check whether emergency access expires and whether its use is reviewed.

Read Pacific’s CMMC evaluation context when framing these controls for a CUI environment. Ask counsel and your ISSM to review the evaluation criteria, system boundary, and acceptable administrative exceptions. A KMS configuration does not establish CMMC certification or guarantee compliance.

3. Prove cross-tenant decrypt fails closed

Do not accept a successful Tenant A decrypt as sufficient testing. Require negative tests using synthetic data:

• 1. Tenant A requests decryption of Tenant B’s ciphertext.
• 2. Tenant A supplies Tenant B’s key ID or alias directly.
• 3. Tenant A submits a forged tenant label or encryption context.
• 4. A shared host agent receives the same unauthorized request.
• 5. A request arrives with missing tenant identity or incomplete context.

Expected result: denial through every supported path, with an attributable event at the enforcement point.

Where supported, bind authenticated tenant identity to required encryption-context conditions. Caller-supplied context is not identity by itself; authenticated callers must not freely choose another tenant’s authorization attributes.

Inspect all applicable policies and grants. A default-deny key policy is insufficient if another effective authorization path permits access. Compare the actual cloud or on-prem KMS semantics, not just similarly named policy fields.

4. Bound grants, rotation, and shared-service authority

Keep this review focused on authorization continuity, not a generic rotation schedule.

When rotating key material or moving to a replacement key resource, ask whether tenant restrictions persist, who updates aliases, and which identities can decrypt historical ciphertext. Rotation does not necessarily revoke old access or invalidate cached plaintext data keys.

Inventory grants by tenant, grantee, permitted operation, purpose, and revocation owner. Prefer constrained, short-lived delegation where supported. Otherwise require an explicit expiry-and-revocation process; do not assume grants expire automatically.

Shared checkpoint agents, storage gateways, backup services, and diagnostic tools deserve special scrutiny. They may hold broad KMS credentials or cached unwrapped data keys even when workloads have narrow permissions.

Require tenant authorization at each shared-service request boundary. Test cache separation and revocation behavior. If privileged host software can read tenant plaintext or cached keys, document that residual host-trust boundary: KMS policy alone does not isolate runtime memory.

5. Demand a reproducible evidence packet

Ask for more than screenshots. A useful packet includes:

• Timestamped key, alias, policy, and grant exports.
• The tenant-to-identity mapping and administrative permission matrix.
• Successful same-tenant tests paired with denied cross-tenant tests.
• Policy-change, alias-change, grant, and rotation records.
• Correlated request IDs showing principal, key, operation, decision, and time.
• Known logging gaps, cache behavior, and unresolved exceptions.

Record the software and configuration versions tested. Preserve evidence without collecting plaintext secrets.

Use Pacific’s GPU capacity and deployment information to anchor the proposed host arrangement, then evaluate its authorization paths. Hardware selection does not determine policy correctness.

Need a focused review of the proposed boundary? Schedule a 30-minute evaluation conversation with Pacific Intelligent Technologies, Inc.. Bring the policy matrix and one failed negative test—not just the architecture diagram.

FAQ

How is this different from general key-management evaluation?

On-prem GPU pod key management addresses the broader operating model. This review asks exactly which tenant identity can authorize each key operation, including delegated paths.

Does tenant-scoped KMS prove tenant isolation?

No. It supports one authorization boundary. Tenant crypto separation is the broader evaluation; shared host privileges and plaintext exposure still matter.

Should rotation frequency be the acceptance criterion?

Not alone. Use secrets rotation cadence for lifecycle timing. Here, require proof that rotation, alias updates, historical decrypt access, and grant revocation preserve tenant restrictions.