Configure customer-managed keys for your Azure Cosmos DB account with Azure Key Vault

APPLIES TO: NoSQL MongoDB Cassandra Gremlin Table

Data stored in your Azure Cosmos DB account is automatically and seamlessly encrypted with keys managed by Microsoft (service-managed keys). Optionally, you can choose to add a second layer of encryption with keys you manage (customer-managed keys or CMK).

Diagram of the layers of encryption around customer data.

You must store customer-managed keys in Azure Key Vault and provide a key for each Azure Cosmos DB account that is enabled with customer-managed keys. This key is used to encrypt all the data stored in that account.

Note

Currently, customer-managed keys are available only for new Azure Cosmos DB accounts. You should configure them during account creation.

Prerequisites

Register the Azure Cosmos DB resource provider

If the Microsoft.DocumentDB resource provider isn't already registered, you should register this provider as a first step.

  1. Sign in to the Azure portal, go to your Azure subscription, and select Resource providers under the Settings tab:

    Screenshot of the Resource providers option in the resource navigation menu.

  2. Search for the Microsoft.DocumentDB resource provider. Verify if the resource provider is already marked as registered. If not, choose the resource provider and select Register:

    Screenshot of the Register option for the Microsoft.DocumentDB resource provider.

Configure your Azure Key Vault instance

Important

Your Azure Key Vault instance must be accessible through public network access or allow trusted Microsoft services to bypass its firewall. An instance that is exclusively accessible through private endpoints cannot be used to host your customer-managed keys.

Using customer-managed keys with Azure Cosmos DB requires you to set two properties on the Azure Key Vault instance that you plan to use to host your encryption keys: Soft Delete and Purge Protection.

  1. If you create a new Azure Key Vault instance, enable these properties during creation:

    Screenshot of Azure Key Vault options including soft delete and purge protection.

  2. If you're using an existing Azure Key Vault instance, you can verify that these properties are enabled by looking at the Properties section on the Azure portal. If any of these properties isn't enabled, see the "Enabling soft-delete" and "Enabling Purge Protection" sections in one of the following articles:

Choosing the preferred security model 

Once purge protection and soft-delete have been enabled, on the access policy tab, you can choose your preferred permission model to use. Access policies are set by default, but Azure role-based access control is supported as well.

The necessary permissions must be given for allowing Cosmos DB to use your encryption key. This step varies depending on whether the Azure Key Vault is using either Access policies or role-based access control.

Note

It is important to note that only one security model can be active at a time, so there is no need to seed the role based access control if the Azure Key Vault is set to use access policies and vice versa)

Add an access policy

In this variation, use the Azure Cosmos DB principal to create an access policy with the appropriate permissions.

  1. From the Azure portal, go to the Azure Key Vault instance that you plan to use to host your encryption keys. Select Access Policies from the left menu:

    Screenshot of the Access policies option in the resource navigation menu.

  2. Select + Add Access Policy.

  3. Under the Key permissions drop-down menu, select Get, Unwrap Key, and Wrap Key permissions:

    Screenshot of access policy permissions including Get, Unwrap key, and Wrap key.

  4. Under Select principal, select None selected.

  5. Search for Azure Cosmos DB principal and select it (to make it easier to find, you can also search by application ID: a232010e-820c-4083-83bb-3ace5fc29d0b for any Azure region except Azure Government regions where the application ID is 57506a73-e302-42a9-b869-6f12d9ec29e9).

    Tip

    This registers the Azure Cosmos DB first-party-identity in your Azure Key Vault access policy. If the Azure Cosmos DB principal isn't in the list, you might need to re-register the Microsoft.DocumentDB resource provider.

  6. Choose Select at the bottom.

    Screenshot of the Select principal option on the Add access policy page.

  7. Select Add to add the new access policy.

  8. Select Save on the Key Vault instance to save all changes.

Adding role-based access control roles

  1. From the Azure portal, go to the Azure Key Vault instance that you plan to use to host your encryption keys. Select Access control (IAM) from the left menu and select Grant access to this resource.

    Screenshot of the Access control option in the resource navigation menu.

    Screenshot of the Grant access to this resource option on the Access control page.

  2. Search the “Key Vault Administrator role” and assign it to yourself. This assignment is done by first searching the role name from the list and then clicking on the “Members” tab. Once on the tab, select the “User, group or service principal” option from the radio and then look up your Azure account. Once the account has been selected, the role can be assigned.

    Screenshot of the Key vault administrator role in the search results.

    Screenshot of a role assignment on the Access control page.

  3. Then, the necessary permissions must be assigned to Cosmos DB’s principal. So, like the last role assignment, go to the assignment page but this time look for the “Key Vault Crypto Service Encryption User” role and on the members tab look for Cosmos DB’s principal. To find the principal, search for Azure Cosmos DB principal and select it.

    Screenshot of the Azure Cosmos DB principal being assigned to a permission.

    Important

    In the Azure Government region, the application ID is 57506a73-e302-42a9-b869-6f12d9ec29e9.

  4. Select Review + assign and the role will be assigned to Cosmos DB.

Validate that the roles have been set correctly

Next, use the access control page to confirm that all roles have been configured correctly.

  1. Once the roles have been assigned, select “View access to this resource” on the Access Control IAM page to verify that everything has been set correctly.

    Screenshot of the View access to resource option on the Access control page.

  2. On the page, set the scope to “this resource” and verify that you have the Key Vault Administrator role, and the Cosmos DB principal has the Key Vault Crypto Encryption User role.

    Screenshot of the scope adjustment option for a role assignment query.

Generate a key in Azure Key Vault

Here, create a new key using Azure Key Vault and retrieve the unique identifier.

  1. From the Azure portal, go the Azure Key Vault instance that you plan to use to host your encryption keys. Then, select Keys from the left menu:

    Screenshot of the Keys option in the resource navigation menu.

  2. Select Generate/Import, provide a name for the new key, and select an RSA key size. A minimum of 3072 is recommended for best security. Then select Create:

    Screenshot of the dialog to create a new key.

  3. After the key is created, select the newly created key and then its current version.

  4. Copy the key's Key Identifier, except the part after the last forward slash:

    Screenshot of the key identifier field and the copy action.

Create a new Azure Cosmos DB account

Create a new Azure Cosmos DB account using the Azure portal or Azure CLI.

When you create a new Azure Cosmos DB account from the Azure portal, choose Customer-managed key in the Encryption step. In the Key URI field, paste the URI/key identifier of the Azure Key Vault key that you copied from the previous step:

Screenshot of the Encryption page with a custom-managed key URI configured.

Using a managed identity in the Azure Key Vault access policy

This access policy ensures that your encryption keys can be accessed by your Azure Cosmos DB account. The access policy is implemented by granting access to a specific Azure Active Directory (AD) identity. Two types of identities are supported:

  • Azure Cosmos DB's first-party identity can be used to grant access to the Azure Cosmos DB service.
  • Your Azure Cosmos DB account's managed identity can be used to grant access to your account specifically.

Not available

Use customer-managed keys with continuous backup

You can create a continuous backup account by using the Azure CLI or an Azure Resource Manager template.

Currently, only user-assigned managed identity is supported for creating continuous backup accounts.

Once the account has been created, you can update the identity to system-assigned managed identity.

Note

System-assigned identity and continuous backup mode is currently under Public Preview and may change in the future.

Alternatively, user can also create a system identity with periodic backup mode first, then migrate the account to Continuous backup mode using these instructions Migrate an Azure Cosmos DB account from periodic to continuous backup mode

Not available

Restore a continuous account that is configured with managed identity

System identity is tied to one specific account and can't be reused in another account. So, a new user-assigned identity is required during the restore process.

Not available

Customer-managed keys and double encryption

The data you store in your Azure Cosmos DB account when using customer-managed keys ends up being encrypted twice:

  • Once through the default encryption performed with Microsoft-managed keys.
  • Once through the extra encryption performed with customer-managed keys.

Double encryption only applies to the main Azure Cosmos DB transactional storage. Some features involve internal replication of your data to a second tier of storage where double encryption isn't provided, even with customer-managed keys. These features include:

Key rotation

Rotating the customer-managed key used by your Azure Cosmos DB account can be done in two ways.

  • Create a new version of the key currently used from Azure Key Vault:

    Screenshot of the New Version option in the Versions page of the Azure portal.

  • Swap the key currently used with a different one by updating the key URI on your account. From the Azure portal, go to your Azure Cosmos DB account and select Data Encryption from the left menu:

    Screenshot of the Data Encryption option on the resource navigation menu.

    Then, replace the Key URI with the new key you want to use and select Save:

    Screenshot of the Save option on the Key page.

    Here's how to do achieve the same result in PowerShell:

    # Variable for resource group name
    $RESOURCE_GROUP_NAME = "<resource-group-name>"
    
    # Variable for account name
    $ACCOUNT_NAME = "<globally-unique-account-name>"
    
    # Variable for new key URI in the key vault
    $NEW_KEY_VAULT_KEY_URI="https://<key-vault-name>.vault.azure.net/keys/<new-key-name>"
    
    $parameters = @{
        ResourceGroupName = $RESOURCE_GROUP_NAME 
        Name = $ACCOUNT_NAME
        ResourceType = "Microsoft.DocumentDb/databaseAccounts"
    }
    $ACCOUNT = Get-AzResource @parameters
    
    $ACCOUNT.Properties.keyVaultKeyUri = $NEW_KEY_VAULT_KEY_URI
    
    $ACCOUNT | Set-AzResource -Force
    

The previous key or key version can be disabled after the Azure Key Vault audit logs don't show activity from Azure Cosmos DB on that key or key version anymore. No more activity should take place on the previous key or key version after 24 hours of key rotation.

Error handling

If there are any errors with customer-managed keys in Azure Cosmos DB, Azure Cosmos DB returns the error details along with an HTTP substatus code in the response. You can use the HTTP substatus code to debug the root cause of the issue. See the HTTP Status Codes for Azure Cosmos DB article to get the list of supported HTTP substatus codes.

Frequently asked questions

Included here are frequently asked questions about setting up customer-managed keys in Azure Cosmos DB.

Are there more charges to enable customer-managed keys?

No, there's no charge to enable this feature.

How do customer-managed keys influence capacity planning?

Request Units consumed by your database operations see an increase to reflect the extra processing required to perform encryption and decryption of your data when using customer-managed keys. The extra RU consumption may lead to slightly higher utilization of your provisioned capacity. Use this table for guidance:

Operation type Request Unit increase
Point-reads (fetching items by their ID) + 5% per operation
Any write operation + 6% per operation | Approximately + 0.06 RU per indexed property
Queries, reading change feed, or conflict feed + 15% per operation

What data gets encrypted with the customer-managed keys?

All the data stored in your Azure Cosmos DB account is encrypted with the customer-managed keys, except for the following metadata:

Are customer-managed keys supported for existing Azure Cosmos DB accounts?

This feature is currently available only for new accounts.

Is it possible to use customer-managed keys with the Azure Cosmos DB analytical store?

Yes, Azure Synapse Link only supports configuring customer-managed keys using your Azure Cosmos DB account's managed identity. You must use your Azure Cosmos DB account's managed identity in your Azure Key Vault access policy before enabling Azure Synapse Link on your account. For a how-to guide on how to enable managed identity and use it in an access policy, see access Azure Key Vault from Azure Cosmos DB using a managed identity.

Is there a plan to support finer granularity than account-level keys?

Not currently, but container-level keys are being considered.

How can I tell if customer-managed keys are enabled on my Azure Cosmos DB account?

From the Azure portal, go to your Azure Cosmos DB account and watch for the Data Encryption entry in the left menu; if this entry exists, customer-managed keys are enabled on your account:

Screenshot of the Data encryption option in the resource navigation menu.

You can also programmatically fetch the details of your Azure Cosmos DB account and look for the presence of the keyVaultKeyUri property.

How do customer-managed keys affect periodic backups?

Azure Cosmos DB takes regular and automatic backups of the data stored in your account. This operation backs up the encrypted data.

The following conditions are necessary to successfully restore a periodic backup:

  • The encryption key that you used at the time of the backup is required and must be available in Azure Key Vault. This condition requires that no revocation was made and the version of the key that was used at the time of the backup is still enabled.
  • If you used a system-assigned managed identity in the access policy, temporarily grant access to the Azure Cosmos DB first-party identity before restoring your data. This requirement exists because a system-assigned managed identity is specific to an account and can't be reused in the target account. Once the data is fully restored to the target account, you can set your desired identity configuration and remove the first-party identity from the Key Vault access policy.

How do customer-managed keys affect continuous backups?

Azure Cosmos DB gives you the option to configure continuous backups on your account. With continuous backups, you can restore your data to any point in time within the past 30 days. To use continuous backups on an account where customer-managed keys are enabled, you must use a user-assigned managed identity in the Key Vault access policy. Azure Cosmos DB first-party identities or system-assigned managed identities aren't currently supported on accounts using continuous backups.

The following conditions are necessary to successfully perform a point-in-time restore:

  • The encryption key that you used at the time of the backup is required and must be available in Azure Key Vault. This requirement means that no revocation was made and the version of the key that was used at the time of the backup is still enabled.
  • You must ensure that the user-assigned managed identity originally used on the source account is still declared in the Key Vault access policy.

Important

If you revoke the encryption key before deleting your account, your account's backup may miss the data written up to 1 hour before the revocation was made.

How do I revoke an encryption key?

Key revocation is done by disabling the latest version of the key:

Screenshot of a disabled custom key version.

Alternatively, to revoke all keys from an Azure Key Vault instance, you can delete the access policy granted to the Azure Cosmos DB principal:

Screenshot of the Delete option for an access policy.

What operations are available after a customer-managed key is revoked?

The only operation possible when the encryption key has been revoked is account deletion.

Next steps