Description

Enable sensitive data encryption at rest using Customer Managed Keys (CMK) rather than Microsoft Managed keys.

Rationale

By default, data in the storage account is encrypted using Microsoft Managed Keys at rest. All Azure Storage resources are encrypted, including blobs, disks, files, queues, and tables. All object metadata is also encrypted. If you want to control and manage this encryption key yourself, however, you can specify a customer-managed key. That key is used to protect and control access to the key that encrypts your data. You can also choose to automatically update the key version used for Azure Storage encryption whenever a new version is available in the associated Key Vault.

While it is possible to automate the assessment of this recommendation, the assessment status for this recommendation remains 'Manual.' This is because the recommendation pertains to storage accounts that store critical data and is therefore not applicable to all storage accounts.

Impact

If the key expires by setting the activation date and expiration date, the user must rotate the key manually.

Using Customer Managed Keys may also incur additional man-hour requirements to create, store, manage, and protect the keys as needed.

Audit

From Azure Console

1. Go to Storage Accounts.
2. For each storage account, under Security + networking, go to Encryption.
3. Ensure that Encryption type is set to Customer-managed keys.

From PowerShell

Connect-AzAccount Set-AzContext -Subscription <subscription id> Get-AzStorageAccount |Select-Object -ExpandProperty Encryption

PowerShell Results - Non-Compliant

KeySource : Microsoft.Storage

PowerShell Results - Compliant

KeySource : Microsoft.Keyvault

From Azure Policy

If referencing a digital copy of this Benchmark, clicking a Policy ID will open a link to the associated Policy definition in Azure.

• Policy ID: 6fac406b-40ca-413b-bf8e-0bf964659c25 - Name: Storage accounts should use customer-managed key for encryption

Default Value

By default, Encryption type is set to Microsoft Managed Keys.

References

1. https://docs.microsoft.com/en-us/azure/storage/common/storage-service-encryption
2. https://docs.microsoft.com/en-us/azure/security/fundamentals/data-encryption-best-practices#protect-data-at-rest
3. https://docs.microsoft.com/en-us/azure/storage/common/storage-service-encryption#azure-storage-encryption-versus-disk-encryption
4. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-data-protection#dp-5-use-customer-managed-key-option-in-data-at-rest-encryption-when-required