Configure customer-managed keys in an Azure key vault for an existing storage account

Azure Storage encrypts all data in a storage account at rest. By default, data is encrypted with Microsoft-managed keys. For additional control over encryption keys, you can manage your own keys. Customer-managed keys must be stored in Azure Key Vault or Key Vault Managed Hardware Security Model (HSM).

This article shows how to configure encryption with customer-managed keys for an existing storage account. The customer-managed keys are stored in a key vault.

To learn how to configure customer-managed keys for a new storage account, see Configure customer-managed keys in an Azure key vault for an new storage account.

To learn how to configure encryption with customer-managed keys stored in a managed HSM, see Configure encryption with customer-managed keys stored in Azure Key Vault Managed HSM.

Note

Azure Key Vault and Azure Key Vault Managed HSM support the same APIs and management interfaces for configuration.

Configure the key vault

You can use a new or existing key vault to store customer-managed keys. The storage account and key vault may be in different regions or subscriptions in the same tenant. To learn more about Azure Key Vault, see Azure Key Vault Overview and What is Azure Key Vault?.

Using customer-managed keys with Azure Storage encryption requires that both soft delete and purge protection be enabled for the key vault. Soft delete is enabled by default when you create a new key vault and cannot be disabled. You can enable purge protection either when you create the key vault or after it is created.

Azure Key Vault supports authorization with Azure RBAC via an Azure RBAC permission model. Microsoft recommends using the Azure RBAC permission model over key vault access policies. For more information, see Grant permission to applications to access an Azure key vault using Azure RBAC.

To learn how to create a key vault with the Azure portal, see Quickstart: Create a key vault using the Azure portal. When you create the key vault, select Enable purge protection, as shown in the following image.

Screenshot showing how to enable purge protection when creating a key vault.

To enable purge protection on an existing key vault, follow these steps:

  1. Navigate to your key vault in the Azure portal.
  2. Under Settings, choose Properties.
  3. In the Purge protection section, choose Enable purge protection.

Add a key

Next, add a key to the key vault. Before you add the key, make sure that you have assigned to yourself the Key Vault Crypto Officer role.

Azure Storage encryption supports RSA and RSA-HSM keys of sizes 2048, 3072 and 4096. For more information about supported key types, see About keys.

To learn how to add a key with the Azure portal, see Quickstart: Set and retrieve a key from Azure Key Vault using the Azure portal.

Choose a managed identity to authorize access to the key vault

When you enable customer-managed keys for an existing storage account, you must specify a managed identity that will be used to authorize access to the key vault that contains the key. The managed identity must have permissions to access the key in the key vault.

The managed identity that authorizes access to the key vault may be either a user-assigned or system-assigned managed identity. To learn more about system-assigned versus user-assigned managed identities, see Managed identity types.

Use a user-assigned managed identity to authorize access

When you enable customer-managed keys for a new storage account, you must specify a user-assigned managed identity. An existing storage account supports using either a user-assigned managed identity or a system-assigned managed identity to configure customer-managed keys.

When you configure customer-managed keys with a user-assigned managed identity, the user-assigned managed identity is used to authorize access to the key vault that contains the key. You must create the user-assigned identity before you configure customer-managed keys.

A user-assigned is a standalone Azure resource. To learn more about user-assigned managed identities, see Managed identity types. To learn how to create and manage a user-assigned managed identity, see Manage user-assigned managed identities.

The user-assigned managed identity must have permissions to access the key in the key vault. Assign the Key Vault Crypto Service Encryption User role to the user-assigned managed identity with key vault scope to grant these permissions.

Before you can configure customer-managed keys with a user-assigned managed identity, you must assign the Key Vault Crypto Service Encryption User role to the user-assigned managed identity, scoped to the key vault. This role grants the user-assigned managed identity permissions to access the key in the key vault. For more information on assigning Azure RBAC roles with the Azure portal, see Assign Azure roles using the Azure portal.

When you configure customer-managed keys with the Azure portal, you can select an existing user-assigned identity through the portal user interface.

Use a system-assigned managed identity to authorize access

A system-assigned managed identity is associated with an instance of an Azure service, in this case an Azure Storage account. You must explicitly assign a system-assigned managed identity to a storage account before you can use the system-assigned managed identity to authorize access to the key vault that contains your customer-managed key.

Only existing storage accounts can use a system-assigned identity to authorize access to the key vault. New storage accounts must use a user-assigned identity, if customer-managed keys are configured on account creation.

The system-assigned managed identity must have permissions to access the key in the key vault. Assign the Key Vault Crypto Service Encryption User role to the system-assigned managed identity with key vault scope to grant these permissions.

Before you can configure customer-managed keys with a system-assigned managed identity, you must assign the Key Vault Crypto Service Encryption User role to the system-assigned managed identity, scoped to the key vault. This role grants the system-assigned managed identity permissions to access the key in the key vault. For more information on assigning Azure RBAC roles with the Azure portal, see Assign Azure roles using the Azure portal.

When you configure customer-managed keys with the Azure portal with a system-assigned managed identity, the system-assigned managed identity is assigned to the storage account for you under the covers.

Configure customer-managed keys for an existing account

When you configure encryption with customer-managed keys for an existing storage account, you can choose to automatically update the key version used for Azure Storage encryption whenever a new version is available in the associated key vault. Alternately, you can explicitly specify a key version to be used for encryption until the key version is manually updated.

You can use either a system-assigned or user-assigned managed identity to authorize access to the key vault when you configure customer-managed keys for an existing storage account.

Note

To rotate a key, create a new version of the key in Azure Key Vault. Azure Storage does not handle key rotation, so you will need to manage rotation of the key in the key vault. You can configure key auto-rotation in Azure Key Vault or rotate your key manually.

Configure encryption for automatic updating of key versions

Azure Storage can automatically update the customer-managed key that is used for encryption to use the latest key version from the key vault. Azure Storage checks the key vault daily for a new version of the key. When a new version becomes available, then Azure Storage automatically begins using the latest version of the key for encryption.

Important

Azure Storage checks the key vault for a new key version only once daily. When you rotate a key, be sure to wait 24 hours before disabling the older version.

To configure customer-managed keys for an existing account with automatic updating of the key version in the Azure portal, follow these steps:

  1. Navigate to your storage account.

  2. On the Settings blade for the storage account, select Encryption. By default, key management is set to Microsoft Managed Keys, as shown in the following image.

    Screenshot showing encryption options in Azure portal.

  3. Select the Customer Managed Keys option.

  4. Choose the Select from Key Vault option.

  5. Select Select a key vault and key.

  6. Select the key vault containing the key you want to use. You can also create a new key vault.

  7. Select the key from the key vault. You can also create a new key.

    Screenshot showing how to select key vault and key in Azure portal.

  8. Select the type of identity to use to authenticate access to the key vault. The options include System-assigned (the default) or User-assigned. To learn more about each type of managed identity, see Managed identity types.

    1. If you select System-assigned, the system-assigned managed identity for the storage account is created under the covers, if it doesn't already exist.
    2. If you select User-assigned, then you must select an existing user-assigned identity that has permissions to access the key vault. To learn how to create a user-assigned identity, see Manage user-assigned managed identities.

    Screenshot showing how to select a user-assigned managed identity for key vault authentication.

  9. Save your changes.

After you've specified the key, the Azure portal indicates that automatic updating of the key version is enabled and displays the key version currently in use for encryption. The portal also displays the type of managed identity used to authorize access to the key vault and the principal ID for the managed identity.

Screenshot showing automatic updating of the key version enabled.

Configure encryption for manual updating of key versions

If you prefer to manually update the key version, then explicitly specify the version at the time that you configure encryption with customer-managed keys. In this case, Azure Storage won't automatically update the key version when a new version is created in the key vault. To use a new key version, you must manually update the version used for Azure Storage encryption.

To configure customer-managed keys with manual updating of the key version in the Azure portal, specify the key URI, including the version. To specify a key as a URI, follow these steps:

  1. To locate the key URI in the Azure portal, navigate to your key vault, and select the Keys setting. Select the desired key, then select the key to view its versions. Select a key version to view the settings for that version.

  2. Copy the value of the Key Identifier field, which provides the URI.

    Screenshot showing key vault key URI in Azure portal.

  3. In the Encryption key settings for your storage account, choose the Enter key URI option.

  4. Paste the URI that you copied into the Key URI field. Omit the key version from the URI to enable automatic updating of the key version.

    Screenshot showing how to enter key URI in Azure portal.

  5. Specify the subscription that contains the key vault.

  6. Specify either a system-assigned or user-assigned managed identity.

  7. Save your changes.

Change the key

You can change the key that you are using for Azure Storage encryption at any time.

To change the key with the Azure portal, follow these steps:

  1. Navigate to your storage account and display the Encryption settings.
  2. Select the key vault and choose a new key.
  3. Save your changes.

Revoke customer-managed keys

Revoking a customer-managed key removes the association between the storage account and the key vault.

To revoke customer-managed keys with the Azure portal, disable the key as described in Disable customer-managed keys.

Disable customer-managed keys

When you disable customer-managed keys, your storage account is once again encrypted with Microsoft-managed keys.

To disable customer-managed keys in the Azure portal, follow these steps:

  1. Navigate to your storage account and display the Encryption settings.
  2. Deselect the checkbox next to the Use your own key setting.

Next steps