Key Sovereignty & Custody (BYOK/HYOK, EU HSM/KMS)
Why important?
Control over cryptographic keys is the most effective technical sovereignty boundary against operator and third-country access.
How measured?
Scale 0–5 + N/A:
- 0 = No customer control over keys; provider-managed keys only; the operator can decrypt at any time.
- 1 = BYOK only claimed/announced; key or HSM location and operation unclear.
- 2 = BYOK available, but KMS/HSM not demonstrably EU-operated or no external custody option.
- 3 = BYOK plus EU-operated KMS/HSM; external key custody possible; operator access restricted contractually/technically.
- 4 = HYOK or customer-held keys widely available; EU-certified HSM; the operator generally cannot decrypt without customer keys.
- 5 = HYOK throughout with customer-held keys; EU-certified HSM (e.g. eIDAS/CC) + verifiable evidence; technical exclusion of operator decryption evidenced.
- N/A = no reliable evidence
Sources / Evidence
Validation questions (RFP)
- Which KMS/HSM options exist (BYOK, HYOK, external key store)? Where are the HSMs located, who operates them, and with which certification (e.g. FIPS 140-3, Common Criteria)? Is it technically impossible for the provider to access keys, and how are key custody, rotation and access logged?
Scores comparison
| Provider | Score | |
|---|---|---|
| AWS European Sovereign Cloud | 4.0 | AWS KMS with CMK/BYOK; CloudHSM (FIPS 140-2 L3); External Key Store (XKS) enables customer-held keys outside AWS (HYOK, "kill switch"). ESC operated in the EU; Nitro/Enclaves reduce operator access. eIDAS HSM/consistency per service to be checked. (stated) |
| STACKIT | 4.0 | STACKIT KMS (GA): HSM-backed (FIPS 140-2 L3, keys never leave the HSM), BYOK (import), AES-256-GCM/RSA, rotation, audit logs; keys exclusively in DE data centres. Confidential Server/Kubernetes (AMD SEV-SNP / Intel TDX) excludes operator access at runtime. (stated) |
| Oracle EU Sovereign Cloud | 4.0 | OCI Vault BYOK; OCI Dedicated KMS (single-tenant FIPS 140-2 L3 HSM partitions, customer-owned, PKCS#11); external KMS/HYOK via Thales CCKM (keys outside OCI). EU Sovereign Cloud operated by dedicated EU legal entities; confidential computing. (stated) |
| Microsoft Sovereign Cloud | 4.0 | Azure Key Vault Managed HSM (FIPS 140-3 L3), CMK/BYOK; Double Key Encryption (DKE) as a customer-held second key (HYOK-like); confidential VMs (AMD SEV-SNP / Intel TDX). EU Data Boundary, keys in an EU region. US parent (see legal axis). (stated) |
| Cloud Temple Trusted Cloud | 4.0 | SecNumCloud (ANSSI) enforces strict key/access controls and operator exclusion by design; HSM/key management within the qualified scope; no explicit confidential computing (SGX/SEV). EU/FR. (stated) |
| OVHcloud Public Cloud (inkl. SecNumCloud) | 3.0 | OVHcloud KMS: CMK/BYOK (import), KMIP API (portability/reversibility), open source SDK/CLI; ISO 27001 + FIPS 140-2 L2 certification in progress. SGX/AMD SEV on bare metal (TEE). SecNumCloud scope. HYOK "coming soon". EU/FR. (stated) |
| T Cloud Public | 3.0 | T Cloud KMS (Cloud KMS): HSM-backed, BYOK (import own keys), customer master keys with 'grant master key' for temporary access, central key management for OBS/RDS/apps, console and Cloud Trace audit. (evidenced) |
| Exoscale | 3.0 | Object storage SSE-C with customer-held key and managed KMS available; no confidential computing documented. EU/CH. (evidenced) |
| Scaleway | 3.0 | Scaleway Key Manager (GA): CMK/BYOK (import via HKDF/SHA-256), keys never leave the Key Manager, rotation/revocation, Secret Manager. No HSM/confidential computing documented. EU/FR. (stated) |
| Delos Cloud | 3.0 | Azure Key Vault / Managed HSM within the sovereign boundary; Microsoft without general access, security-cleared staff (DE); BYOK via Azure key management. (verify → evidenced) |
| IONOS Cloud | 2.0 | SSE-C (server-side encryption with customer-provided keys) for object storage publicly documented (API/SDK; DCD only SSE-S3); block storage at rest AES-XTS-256 (key per volume, provider-side). No managed KMS/HSM (in development according to the provider). |
| pluscloud open | 2.0 | pluscloud open (SCS/OpenStack): customer-side encryption excludes operator access to encrypted data; no confidential computing, managed options with admin access; Barbican KMS possible in principle. EU/DE. (partial) |
| Hetzner Cloud | 2.0 | IaaS without managed KMS/HSM; customer-side encryption (DIY/LUKS) possible, keys thus remain with the customer; no confidential computing. EU/DE. (partial) |
| SysEleven OpenStack Cloud | 2.0 | OpenStack Barbican (KMS) available (managed K8s); no dedicated BYOK/HYOK concept advertised. |
| Infomaniak Public Cloud | 2.0 | OpenStack public cloud without managed KMS/HSM/secrets manager; customer-side encryption possible; no confidential computing. Swiss sovereignty focus. (partial) |
| UpCloud | 1.0 | Server-side encryption available; no managed KMS/HSM or BYOK service found (as of 2026-06). (Privileged access via EU Access Management Policy, see operator access cell.) |
| noris Sovereign Cloud | 1.0 | OpenStack/Gardener basis; no documented customer key management/BYOK advertised (OpenStack Barbican possibly available, not stated). (not evidenced) |