# BSI C5:2020 CRY-03 — Encryption of sensitive data for storage - Source: https://support.icompaas.com/compliance/bsi-c5-2020/cry-03-encryption-of-sensitive-data-for-storage - Section: [Compliance](https://support.icompaas.com/compliance) › [BSI C5:2020 (Cloud Computing Compliance Criteria)](https://support.icompaas.com/compliance/bsi-c5-2020) › Cryptography & Key Management (CRY) - Last updated: 2026-06-05 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **BSI C5:2020**·Criterion `CRY-03`·critical·Component: **Cryptography & Key Management** ## What this control requires > Encrypts stored customer data with private keys known only to customers, per legal requirements. Specifies exceptions via contractual agreements, ensuring confidentiality of cloud customer data at rest through robust encryption procedures. > > — BSI C5:2020, Criterion CRY-03 ### In plain English Encrypts stored customer data with private keys known only to customers, per legal requirements. In practice, this means you can prove you exceptions agreements-level controls on a defined cadence. ## Why it matters BSI C5 is the default cloud-security baseline German public-sector buyers and many DAX-listed enterprises expect; gaps here directly block procurement in the DACH region and frequently appear as must-have items in EU public-tender documents. This control is rated **critical** in the source catalogue. Treat gaps here as production incidents in the risk register, not housekeeping. ## What an auditor looks for A C5 attesting auditor (under ISAE 3000 / IDW PS 860) tests both the design and — for a Type 2 — the operating effectiveness over the attestation period. For each criterion they look for both the Basic and any in-scope Additional objectives. Within **Cryptography & Key Management**, the assessor will trace your implementation back to the catalogue reference (Criterion CRY-03) and look for objective evidence on the latest two assessment cycles. ## How to implement #### Cloud Posture **CSPM.** Run Wiz / Prisma / Defender for Cloud / Security Command Center over every account; auto-ticket findings above your accepted-risk threshold. #### Configuration Management **Policy-as-code.** Codify the control as Service Control Policies (AWS), Azure Policy initiatives, or Organisation Policy (GCP) so the platform enforces what the document promises. **IaC.** Gate Terraform / Pulumi / CloudFormation changes with Checkov / tfsec / OPA so misconfigurations never reach production. **Drift.** Run a CSPM (Wiz / Prisma / Defender for Cloud / Security Command Center) over every account and route findings to a single risk register. #### Network Security **AWS.** VPC Flow Logs to S3, default-deny security groups, AWS Network Firewall for north-south, and Transit Gateway for hub-and-spoke segmentation. **Azure.** NSGs with deny-by-default, Azure Firewall Premium with TLS inspection, Private Endpoints for PaaS, and Microsoft Defender for Cloud's secure score for drift. **GCP.** VPC Service Controls perimeters around sensitive APIs, Cloud NGFW Enterprise for L7 inspection, Private Service Connect for managed services. ### Operational checklist - **Exceptions.** Document the trigger, the owner and the cadence. - **Security.** Document the trigger, the owner and the cadence. - **Confidentiality.** Document the trigger, the owner and the cadence. - **Protection.** Document the trigger, the owner and the cadence. - **Data.** Document the trigger, the owner and the cadence. - **Scope:** agreements, protection, - configuration, cloud customer data, key management. ## Evidence to collect - **Infra Scan.** Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings. Infrastructure posture tooling (AWS Config, Azure Policy, Nessus) verifies platform hardening. Focus: Encryption of sensitive data for storage. ## Common pitfalls - Treating CSPM findings as a backlog instead of a hot queue: findings older than the policy SLA accumulate until the auditor asks why. - Manual cloud-console changes that never make it back to Terraform — drift accumulates until the next outage forces a reconciliation. - Default-allow egress rules; East-West traffic with no segmentation; jump hosts on the public internet with password auth. ## How it maps to other frameworks Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit. - [**NIST SP 800-171 Rev. 3 3.14.8** — Information Management and Retention](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-14-8-information-management-and-retention) - [**NIST SP 800-53 Rev. 5 CP-9(3)** — Separate Storage For Critical Information](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/cp-9-3-separate-storage-for-critical-information) - [**ISO/IEC 27001:2022 A.5.34** — Privacy and protection of personal identifiable information (PII)](https://support.icompaas.com/compliance/iso-27001-2022/a-5-34-privacy-and-protection-of-personal-identifiable-information-pii) - [**CIS Controls v8 11.3** — Protect Recovery Data](https://support.icompaas.com/compliance/cis-controls-v8/11-3-protect-recovery-data) ## Related controls in BSI C5:2020 - [**Criterion CRY-04** — Secure key management](https://support.icompaas.com/compliance/bsi-c5-2020/cry-04-secure-key-management) - [**Criterion CRY-02** — Encryption of data for transmission (transport encryption)](https://support.icompaas.com/compliance/bsi-c5-2020/cry-02-encryption-of-data-for-transmission-transport-encryption) - [**Criterion PI-03** — Secure deletion of data](https://support.icompaas.com/compliance/bsi-c5-2020/pi-03-secure-deletion-of-data) - [**Criterion COS-04** — Cross-network access](https://support.icompaas.com/compliance/bsi-c5-2020/cos-04-cross-network-access) - [**Criterion INQ-01** — Legal Assessment of Investigative Inquiries](https://support.icompaas.com/compliance/bsi-c5-2020/inq-01-legal-assessment-of-investigative-inquiries) - [**Criterion DEV-06** — Testing changes](https://support.icompaas.com/compliance/bsi-c5-2020/dev-06-testing-changes) ## References - [Bundesamt für Sicherheit in der Informationstechnik (BSI) — BSI C5:2020](https://www.bsi.bund.de/EN/Topics/CloudComputing/Compliance_Criteria_Catalogue/Compliance_Criteria_Catalogue_node.html) - Catalogue identifier: `Criterion CRY-03` Topics: data protectioncloud infrastructurecloud postureconfiguration managementnetwork securityapi security ## Related compliance guidance - [SOC 2 compliance: a practical implementation guide for cloud-native SaaS teams](https://support.icompaas.com/compliance/soc-2-trust-services-criteria): Configuration checks like this one are the technical half of a SOC 2 / ISO 27001 programme — the guide shows where they fit, what else an auditor expects, and how to evidence them. - [ISO/IEC 27001:2022 compliance: a practical implementation guide](https://support.icompaas.com/compliance/iso-27001-2022): ISO 27001 Annex A.8 (technological controls) is where cloud hardening evidence lands; the guide shows how to run the ISMS around it.