Secure your key vault

Azure Key Vault is a cloud service that safeguards encryption keys and secrets (such as certificates, connection strings, passwords) for your cloud applications. Since this data is sensitive and business critical, you want to secure access to your key vaults so that only authorized applications and users can access key vault. This article provides an overview of key vault access model, explains authentication and authorization, and describes how to secure access to key vault for your cloud applications with an example.

Overview

Access to a key vault is controlled through two separate interfaces: management plane and data plane. For both planes proper authentication and authorization is required before a caller (a user or an application) can get access to key vault. Authentication establishes the identity of the caller, while authorization determines what operations the caller is allowed to perform.

For authentication both management plane and data plane use Azure Active Directory. For authorization, management plane uses role-based access control (RBAC) while data plane uses key vault access policy.

Here is a brief overview of the topics covered:

Authentication using Azure Active Directory - This section explains how a caller authenticates with Azure Active Directory to access a key vault via management plane and data plane.

Management plane and data plane - Management plane and data plane are two access planes used for accessing your key vault. Each access plane supports specific operations. This section describes the access endpoints, operations supported, and access control method used by each plane.

Management plane access control - In this section we'll look at allowing access to management plane operations using role-based access control.

Data plane access control - This section describes how to use key vault access policy to control data plane access.

Example - This example describes how to setup access control for your key vault to allow three different teams (security team, developers/operators, and auditors) to perform specific tasks to develop, manage and monitor an application in Azure.

Authentication using Azure Active Directory

When you create a key vault in an Azure subscription, it is automatically associated with the subscription's Azure Active Directory tenant. All callers (users and applications) must be registered in this tenant to access this key vault. An application or a user must authenticate with Azure Active Directory to access key vault. This applies to both management plane and data plane access. In both cases, an application can access key vault in two ways:

  • user+app access - usually this is for applications that access key vault on behalf of a signed-in user. Azure PowerShell, Azure Portal are examples of this type of access. There are two ways to grant access to users: one way is to grant access to users so they can access key vault from any application and the other way is to grant a user access to key vault only when they use a specific application (referred to as compound identity).
  • app-only access - for applications that run daemon services, background jobs etc. The application's identity is granted access to the key vault.

In both types of applications, the application authenticates with Azure Active Directory using any of the supported authentication methods and acquires a token. Authentication method used depends on the application type. Then the application uses this token and sends REST API request to key vault. In case of management plane access the requests are routed through Azure Resource Manager endpoint. When accessing data plane, the applications talks directly to a key vault endpoint. See more details on the whole authentication flow.

The resource name for which the application requests a token is different depending on whether the application is accessing management plane or data plane. Hence the resource name is either management plane or data plane endpoint described in the table in a later section, depending on the Azure environment.

Having one single mechanism for authentication to both management and data plane has its own benefits:

  • Organizations can centrally control access to all key vaults in their organization
  • If a user leaves, they instantly lose access to all key vaults in the organization
  • Organizations can customize authentication via the options in Azure Active Directory (for example, enabling multi-factor authentication for added security)

Management plane and data plane

Azure Key Vault is an Azure service available via Azure Resource Manager deployment model. When you create a key vault, you get a virtual container inside which you can create other objects like keys, secrets, and certificates. Then you access your key vault using management plane and data plane to perform specific operations. Management plane interface is used to manage your key vault itself, such as creating, deleting, updating key vault attributes and setting access policies for data plane. Data plane interface is used to add, delete, modify, and use the keys, secrets, and certificates stored in your key vault.

The management plane and data plane interfaces are accessed through different endpoints (see table). The second column in the table describes the DNS names for these endpoints in different Azure environments. The third column describes the operations you can perform from each access plane. Each access plane also has its own access control mechanism: for management plane access control is set using Azure Resource Manager Role-Based Access Control (RBAC), while for data plane access control is set using key vault access policy.

Access plane Access endpoints Operations Access control mechanism
Management plane Global:
management.azure.com:443

Azure China:
management.chinacloudapi.cn:443

Azure US Government:
management.usgovcloudapi.net:443

Azure Germany:
management.microsoftazure.de:443
Create/Read/Update/Delete key vault
Set access policies for key vault
Set tags for key vault
Azure Resource Manager Role-Based Access Control (RBAC)
Data plane Global:
<vault-name>.vault.azure.net:443

Azure China:
<vault-name>.vault.azure.cn:443

Azure US Government:
<vault-name>.vault.usgovcloudapi.net:443

Azure Germany:
<vault-name>.vault.microsoftazure.de:443
For Keys: Decrypt, Encrypt, UnwrapKey, WrapKey, Verify, Sign, Get, List, Update, Create, Import, Delete, Backup, Restore

For secrets: Get, List, Set, Delete
Key vault access policy

The management plane and data plane access controls work independently. For example, if you want to grant an application access to use keys in a key vault, you only need to grant data plane access permissions using key vault access policies and no management plane access is needed for this application. And conversely, if you want a user to be able to read vault properties and tags, but not have any access to keys, secrets, or certificates, you can grant this user, 'read' access using RBAC and no access to data plane is required.

Management plane access control

The management plane consists of operations that affect the key vault itself. For example, you can create or delete a key vault. You can get a list of vaults in a subscription. You can retrieve key vault properties (such as SKU, tags) and set key vault access policies that control the users and applications that can access keys and secrets in the key vault. Management plane access control uses RBAC. See the complete list of key vault operations that can be performed via management plane in the table in preceding section.

Role-based Access Control (RBAC)

Each Azure subscription has an Azure Active Directory. Users, groups, and applications from this directory can be granted access to manage resources in the Azure subscription that use the Azure Resource Manager deployment model. This type of access control is referred to as Role-Based Access Control (RBAC). To manage this access, you can use the Azure portal, the Azure CLI tools, PowerShell, or the Azure Resource Manager REST APIs.

With the Azure Resource Manager model, you create your key vault in a resource group and control access to the management plane of this key vault by using Azure Active Directory. For example, you can grant users or a group ability to manage key vaults in a specific resource group.

You can grant access to users, groups and applications at a specific scope by assigning appropriate RBAC roles. For example, to grant access to a user to manage key vaults you would assign a predefined role 'key vault Contributor' to this user at a specific scope. The scope in this case would be either a subscription, a resource group, or just a specific key vault. A role assigned at subscription level applies to all resource groups and resources within that subscription. A role assigned at resource group level applies to all resources in that resource group. A role assigned for a specific resource only applies to that resource. There are several predefined roles (see RBAC: Built-in roles), and if the predefined roles do not fit your needs you can also define your own roles.

Important

Note that if a user has Contributor permissions (RBAC) to a key vault management plane, she can grant herself access to data plane, by setting key vault access policy, which controls access to data plane. Therefore, it is recommended to tightly control who has 'Contributor' access to your key vaults to ensure only authorized persons can access and manage your key vaults, keys, secrets, and certificates.

Data plane access control

The key vault data plane consists of operations that affect the objects in a key vault, such as keys, secrets, and certificates. This includes key operations such as create, import, update, list, backup, and restore keys, cryptographic operations such as sign, verify, encrypt, decrypt, wrap, and unwrap, and set tags and other attributes for keys. Similarly, for secrets it includes, get, set, list, delete.

Data plane access is granted by setting access policies for a key vault. A user, group, or an application must have Contributor permissions (RBAC) for management plane for a key vault to be able to set access policies for that key vault. A user, group, or application can be granted access to perform specific operations for keys or secrets in a key vault. Key vault support up to 16 access policy entries for a key vault. Create an Azure Active Directory security group and add users to that group to grant data plane access to several users to a key vault.

Key vault Access Policies

Key vault access policies grant permissions to keys, secrets and certificates separately. For example, you can give a user access to only keys, but no permissions for secrets. However, permissions to access keys or secrets or certificates are at the vault level. In other words, key vault access policy does not support object level permissions. You can use Azure portal, the Azure CLI tools, PowerShell, or the key vault Management REST APIs to set access policies for a key vault.

Important

Note that key vault access policies apply at the vault level. For example, when a user is granted permission to create and delete keys, she can perform those operations on all keys in that key vault.

Example

Let's say you are developing an application that uses a certificate for SSL, Azure storage for storing data, and uses an RSA 2048-bit key for sign operations. Let's say this application is running in a VM (or a VM Scale Set). You can use a key vault to store all the application secrets, and use key vault to store the bootstrap certificate that is used by the application to authenticate with Azure Active Directory.

So, here's a summary of all the keys and secrets to be stored in a key vault.

  • SSL Cert - used for SSL
  • Storage Key - used to get access to Storage account
  • RSA 2048-bit key - used for sign operations
  • Bootstrap certificate - used to authenticate to Azure Active Directory, to get access to key vault to fetch the storage key and use the RSA key for signing.

Now let's meet the people who are managing, deploying and auditing this application. We'll use three roles in this example.

  • Security team - These are typically IT staff from the 'office of the CSO (Chief Security Officer)' or equivalent, responsible for the proper safekeeping of secrets such as SSL certificates, RSA keys used for signing, connection strings for databases, storage account keys.
  • Developers/operators - These are the folks who develop this application and then deploy it in Azure. Typically, they are not part of the security team, and hence they should not have access to any sensitive data, such as SSL certificates, RSA keys, but the application they deploy should have access to those.
  • Auditors - This is usually a different set of people, isolated from the developers and general IT staff. Their responsibility is to review proper use and maintenance of certificates, keys, etc. and ensure compliance with data security standards.

There is one more role that is outside the scope of this application, but relevant here to be mentioned, and that would be the subscription (or resource group) administrator. Subscription administrator sets up initial access permissions for the security team. Here we assume that the subscription administrator has granted access to the security team to a resource group in which all the resources needed for this application reside.

Now let's see what actions each role performs in the context of this application.

  • Security team
    • Create key vaults
    • Turns on key vault logging
    • Add keys/secrets
    • Create backup of keys for disaster recovery
    • Set key vault access policy to grant permissions to users and applications to perform specific operations
    • Periodically roll keys/secrets
  • Developers/operators
    • Get references to bootstrap and SSL certs (thumbprints), storage key (secret URI) and signing key (Key URI) from security team
    • Develop and deploy application that accesses keys and secrets programmatically
  • Auditors
    • Review usage logs to confirm proper key/secret use and compliance with data security standards

Now let's see what access permissions to key vault are needed by each role (and the application) to perform their assigned tasks.

User Role Management plane permissions Data plane permissions
Security Team key vault Contributor Keys: backup, create, delete, get, import, list, restore
Secrets: all
Developers/Operator key vault deploy permission so that the VMs they deploy can fetch secrets from the key vault None
Auditors None Keys: list
Secrets: list
Application None Keys: sign
Secrets: get
Note

Auditors need list permission for keys and secrets so they can inspect attributes for keys and secrets that are not emitted in the logs, such as tags, activation and expiration dates.

Besides permission to key vault, all three roles also need access to other resources. For example, to be able to deploy VMs (or Web Apps etc.) Developers/Operators also need 'Contributor' access to those resource types. Auditors need read access to the storage account where the key vault logs are stored.

Since the focus of this article is securing access to your key vault, we only illustrate the relevant portions pertaining to this topic and skip details regarding deploying certificates, accessing keys and secrets programmatically etc. Those details are already covered elsewhere. Deploying certificates stored in key vault to VMs is covered in a blog post, and there is sample code available that illustrates how to use bootstrap certificate to authenticate to Azure AD to get access to key vault.

Most of the access permissions can be granted using Azure portal, but to grant granular permissions you may need to use Azure PowerShell (or Azure CLI) to achieve the desired result.

The following PowerShell snippets assume:

  • The Azure Active Directory administrator has created security groups that represent the three roles, namely Contoso Security Team, Contoso App Devops, Contoso App Auditors. The administrator has also added users to the groups they belong.
  • ContosoAppRG is the resource group where all the resources reside. contosologstorage is where the logs are stored.
  • Key vault ContosoKeyVault and storage account used for key vault logs contosologstorage must be in the same Azure location

First the subscription administrator assigns 'key vault Contributor' and 'User Access Administrator' roles to the security team. This allows the security team to manage access to other resources and manage key vaults in the resource group ContosoAppRG.

New-AzureRmRoleAssignment -ObjectId (Get-AzureRmADGroup -SearchString 'Contoso Security Team')[0].Id -RoleDefinitionName "key vault Contributor" -ResourceGroupName ContosoAppRG
New-AzureRmRoleAssignment -ObjectId (Get-AzureRmADGroup -SearchString 'Contoso Security Team')[0].Id -RoleDefinitionName "User Access Administrator" -ResourceGroupName ContosoAppRG

The following script illustrates how the security team can create a key vault, setup logging, and set access permissions for other roles and the application.

# Create key vault and enable logging
$sa = Get-AzureRmStorageAccount -ResourceGroup ContosoAppRG -Name contosologstorage
$kv = New-AzureRmKeyVault -VaultName ContosoKeyVault -ResourceGroup ContosoAppRG -SKU premium -Location 'westus' -EnabledForDeployment
Set-AzureRmDiagnosticSetting -ResourceId $kv.ResourceId -StorageAccountId $sa.Id -Enabled $true -Categories AuditEvent

# Data plane permissions for Security team
Set-AzureRmKeyVaultAccessPolicy -VaultName ContosoKeyVault -ObjectId (Get-AzureRmADGroup -SearchString 'Contoso Security Team')[0].Id -PermissionsToKeys backup,create,delete,get,import,list,restore -PermissionsToSecrets all

# Management plane permissions for Dev/ops
# Create a new role from an existing role
$devopsrole = Get-AzureRmRoleDefinition -Name "Virtual Machine Contributor"
$devopsrole.Id = $null
$devopsrole.Name = "Contoso App Devops"
$devopsrole.Description = "Can deploy VMs that need secrets from key vault"
$devopsrole.AssignableScopes = @("/subscriptions/<SUBSCRIPTION-GUID>")

# Add permission for dev/ops so they can deploy VMs that have secrets deployed from key vaults
$devopsrole.Actions.Add("Microsoft.KeyVault/vaults/deploy/action")
New-AzureRmRoleDefinition -Role $devopsrole

# Assign this newly defined role to Dev ops security group
New-AzureRmRoleAssignment -ObjectId (Get-AzureRmADGroup -SearchString 'Contoso App Devops')[0].Id -RoleDefinitionName "Contoso App Devops" -ResourceGroupName ContosoAppRG

# Data plane permissions for Auditors
Set-AzureRmKeyVaultAccessPolicy -VaultName ContosoKeyVault -ObjectId (Get-AzureRmADGroup -SearchString 'Contoso App Auditors')[0].Id -PermissionsToKeys list -PermissionsToSecrets list

The custom role defined, is only assignable to the subscription where the ContosoAppRG resource group is created. If the same custom roles will be used for other projects in other subscriptions, it's scope could have more subscriptions added.

The custom role assignment for the developers/operators for the "deploy/action" permission is scoped to the resource group. This way only the VMs created in the resource group 'ContosoAppRG' will get the secrets (SSL cert and bootstrap cert). Any VMs that a member of dev/ops team creates in other resource group will not be able to get these secrets even if they knew the secret URIs.

This example depicts a simple scenario. Real life scenarios may be more complex and you may need to adjust permissions to your key vault based on your needs. For example, in our example, we assume that security team will provide the key and secret references (URIs and thumbprints) that developers/operators team need to reference in their applications. Hence, they don't need to grant developers/operators any data plane access. Also, note that this example focuses on securing your key vault. Similar consideration should be given to secure your VMs, storage accounts and other Azure resources too.

Note

Note: This example shows how key vault access will be locked down in production. The developers should have their own subscription or resourcegroup where they have full permissions to manage their vaults, VMs and storage account where they develop the application.

Resources

Next Steps

For a getting started tutorial for an administrator, see Get Started with Azure key vault.

For more information about usage logging for key vault, see Azure key vault Logging.

For more information about using keys and secrets with Azure key vault, see About Keys and Secrets.

If you have questions about key vault, visit the Azure key vault Forums