Configure customer-managed key encryption at rest in Azure VMware Solution

This article illustrates how to encrypt VMware vSAN Key Encryption Keys (KEKs) with customer-managed keys (CMKs) managed by customer-owned Azure Key Vault.

When CMK encryptions are enabled on your Azure VMware Solution private cloud, Azure VMware Solution uses the CMK from your key vault to encrypt the vSAN KEKs. Each ESXi host that participates in the vSAN cluster uses randomly generated Disk Encryption Keys (DEKs) that ESXi uses to encrypt disk data at rest. vSAN encrypts all DEKs with a KEK provided by Azure VMware Solution key management system (KMS). Azure VMware Solution private cloud and Azure Key Vault don't need to be in the same subscription.

When managing your own encryption keys, you can do the following actions:

  • Control Azure access to vSAN keys.
  • Centrally manage the lifecycle of CMKs.
  • Revoke Azure from accessing the KEK.

The Customer-managed keys (CMKs) feature supports the following key types. See the following key types, shown by key type and key size.

  • RSA: 2048, 3072, 4096
  • RSA-HSM: 2048, 3072, 4096

Topology

The following diagram shows how Azure VMware Solution uses Azure Active Directory (Azure AD) and a key vault to deliver the customer-managed key.

Diagram showing the customer-managed keys topology.

Prerequisites

Before you begin to enable customer-managed key (CMK) functionality, ensure the following listed requirements are met:

  • You'll need an Azure Key Vault to use CMK functionality. If you don't have an Azure Key Vault, you can create one using Quickstart: Create a key vault using the Azure portal.

  • If you enabled restricted access to key vault, you'll need to allow Microsoft Trusted Services to bypass the Azure Key Vault firewall. Go to Configure Azure Key Vault networking settings to learn more.

    Note

    After firewall rules are in effect, users can only perform Key Vault data plane operations when their requests originate from allowed VMs or IPv4 address ranges. This also applies to accessing key vault from the Azure portal. This also affects the key vault Picker by Azure VMware Solution. Users may be able to see a list of key vaults, but not list keys, if firewall rules prevent their client machine or user does not have list permission in key vault.

  • Enable System Assigned identity on your Azure VMware Solution private cloud if you didn't enable it during software-defined data center (SDDC) provisioning.

    Use the following steps to enable System Assigned identity:

    1. Sign in to Azure portal.

    2. Navigate to Azure VMware Solution and locate your SDDC.

    3. From the left navigation, open Manage and select Identity.

    4. In System Assigned, check Enable and select Save.

      1. System Assigned identity should now be enabled.

    Once System Assigned identity is enabled, you'll see the tab for Object ID. Make note of the Object ID for use later.

  • Configure the key vault access policy to grant permissions to the managed identity. It will be used to authorize access to the key vault.

    1. Sign in to Azure portal.
    2. Navigate to Key vaults and locate the key vault you want to use.
    3. From the left navigation, under Settings, select Access policies.
    4. In Access policies, select Add Access Policy.
      1. From the Key Permissions drop-down, check Select all, Unwrap Key, and Wrap Key.
      2. Under Select principal, select None selected. A new Principal window with a search box will open.
      3. In the search box, paste the Object ID from the previous step, or search the private cloud name you want to use. Choose Select when you're done.
      4. Select ADD.
      5. Verify the new policy appears under the current policy's Application section.
      6. Select Save to commit changes.

Customer-managed key version lifecycle

You can change the customer-managed key (CMK) by creating a new version of the key. The creation of a new version won't interrupt the virtual machine (VM) workflow.

In Azure VMware Solution, CMK key version rotation will depend on the key selection setting you've chosen during CMK setup.

Key selection setting 1

A customer enables CMK encryption without supplying a specific key version for CMK. Azure VMware Solution selects the latest key version for CMK from the customer's key vault to encrypt the vSAN Key Encryption Keys (KEKs). Azure VMware Solution tracks the CMK for version rotation. When a new version of the CMK key in Azure Key Vault is created, it's captured by Azure VMware Solution automatically to encrypt vSAN KEKs.

Note

Azure VMware Solution can take up to ten minutes to detect a new auto-rotated key version.

Key selection setting 2

A customer can enable CMK encryption for a specified CMK key version to supply the full key version URI under the Enter Key from URI option. When the customer's current key expires, they'll need to extend the CMK key expiration or disable CMK.

Enable CMK with system-assigned identity

System-assigned identity is restricted to one per resource and is tied to the lifecycle of the resource. You can grant permissions to the managed identity on Azure resource. The managed identity is authenticated with Azure AD, so you don't have to store any credentials in code.

Important

Ensure that key vault is in the same region as the Azure VMware Solution private cloud.

Navigate to your Azure Key Vault and provide access to the SDDC on Azure Key Vault using the Principal ID captured in the Enable MSI tab.

  1. From your Azure VMware Solution private cloud, under Manage, select Encryption, then select Customer-managed keys (CMK).

  2. CMK provides two options for Key Selection from Azure Key Vault.

    Option 1

    1. Under Encryption key, choose the select from Key Vault button.
    2. Select the encryption type, then the Select Key Vault and key option.
    3. Select the Key Vault and key from the drop-down, then choose Select.

    Option 2

    1. Under Encryption key, choose the Enter key from URI button.
    2. Enter a specific Key URI in the Key URI box.

    Important

    If you want to select a specific key version instead of the automatically selected latest version, you'll need to specify the key URI with key version. This will affect the CMK key version life cycle.

  3. Select Save to grant access to the resource.

Change from customer-managed key to Microsoft managed key

When a customer wants to change from a customer-managed key (CMK) to a Microsoft managed key (MMK), it won't interrupt VM workload. To make the change from CMK to MMK, use the following steps.

  1. Select Encryption, located under Manage from your Azure VMware Solution private cloud.
  2. Select Microsoft-managed keys (MMK).
  3. Select Save.

Limitations

The Azure Key Vault must be configured as recoverable.

  • Configure Azure Key Vault with the Soft Delete option.
  • Turn on Purge Protection to guard against force deletion of the secret vault, even after soft delete.

Updating CMK settings won't work if the key is expired or the Azure VMware Solution access key has been revoked.

Troubleshooting and best practices

Accidental deletion of a key

If you accidentally delete your key in the Azure Key Vault, private cloud won't be able to perform some cluster modification operations. To avoid this scenario, we recommend that you keep soft deletes enabled on key vault. This option ensures that, if a key is deleted, it can be recovered within a 90-day period as part of the default soft-delete retention. If you are within the 90-day period, you can restore the key in order to resolve the issue.

Restore key vault permission

If you have a private cloud that lost access to the customer managed key, check if Managed System Identity (MSI) requires permissions in key vault. The error notification returned from Azure may not correctly indicate MSI requiring permissions in key vault as the root cause. Remember, the required permissions are: get, wrapKey, and unwrapKey. See step 4 in Prerequisites.

Fix expired key

If you aren't using the auto-rotate function and the Customer Managed Key has expired in key vault, you can change the expiration date on key.

Restore key vault access

Ensure Managed System Identity (MSI) is used for providing private cloud access to key vault.

Deletion of MSI

If you accidentally delete the Managed System Identity (MSI) associated with private cloud, you'll need to disable CMK, then follow the steps to enable CMK from start.

Next steps

Learn about Azure Key Vault backup and restore

Learn about Azure Key Vault recovery