Import HSM-protected keys to Managed HSM (BYOK)

Azure Key Vault Managed HSM supports importing keys generated in your on-premises hardware security module (HSM). The keys never leave the HSM protection boundary. This scenario is often referred to as bring your own key (BYOK). Managed HSM uses the Marvell LiquidSecurity HSM adapters (FIPS 140-3 Level 3 validated) to protect your keys.

Use the information in this article to help you plan for, generate, and transfer your own HSM-protected keys to use with Managed HSM.

For more information, and for a tutorial to get started using Managed HSM, see What is Managed HSM?

Overview

Here's an overview of the process. Specific steps to complete are described later in the article.

• In Managed HSM, generate a key (referred to as a Key Exchange Key (KEK)). The KEK must be an RSA-HSM key that has only the import key operation.
• Download the KEK public key as a .pem file.
• Transfer the KEK public key to an offline computer that is connected to an on-premises HSM.
• In the offline computer, use the BYOK tool provided by your HSM vendor to create a BYOK file.
• The target key is encrypted with a KEK, which stays encrypted until it's transferred to the Managed HSM. Only the encrypted version of your key leaves the on-premises HSM.
• A KEK that's generated inside a Managed HSM isn't exportable. HSMs enforce the rule that no clear version of a KEK exists outside a Managed HSM.
• The KEK must be in the same managed HSM where the target key will be imported.
• When you upload the BYOK file to Managed HSM, a Managed HSM uses the KEK private key to decrypt the target key material and import it as an HSM key. This operation happens entirely inside the HSM. The target key always remains in the HSM protection boundary.

Prerequisites

An Azure subscription is required. If you don't have one, create a free account before you begin.

You also need:

• Azure CLI version 2.12.0 or later. Run az --version to find the version. If you need to install or upgrade, see Install the Azure CLI.
• A managed HSM in the supported HSMs list in your subscription. To provision and activate a managed HSM, see Quickstart: Provision and activate a managed HSM using Azure CLI.

Azure Cloud Shell

Azure hosts Azure Cloud Shell, an interactive shell environment that you can use through your browser. You can use either Bash or PowerShell with Cloud Shell to work with Azure services. You can use the Cloud Shell preinstalled commands to run the code in this article, without having to install anything on your local environment.

To start Azure Cloud Shell:

Option	Example/Link
Select Try It in the upper-right corner of a code or command block. Selecting Try It doesn't automatically copy the code or command to Cloud Shell.
Go to https://shell.azure.com, or select the Launch Cloud Shell button to open Cloud Shell in your browser.
Select the Cloud Shell button on the menu bar at the upper right in the Azure portal.

To use Azure Cloud Shell:

1. Start Cloud Shell.

2. Select the Copy button on a code block (or command block) to copy the code or command.

3. Paste the code or command into the Cloud Shell session by selecting Ctrl+Shift+V on Windows and Linux, or by selecting Cmd+Shift+V on macOS.

4. Select Enter to run the code or command.

To sign in to Azure by using the CLI, type:

az login

For more information on authentication options through the CLI, see sign in with Azure CLI.

Supported HSMs

Supported key types

Generate and transfer your key to the Managed HSM

Step 1: Generate a KEK

A KEK is an RSA key that you generate in a Managed HSM. Use the KEK to encrypt the key you want to import (the target key).

The KEK must be:

• An RSA-HSM key (2,048-bit, 3,072-bit, or 4,096-bit)
• Generated in the same Managed HSM where you intend to import the target key
• Created with allowed key operations set to import

Use the az keyvault key create command to create a KEK that has key operations set to import. Record the key identifier (kid) that's returned from the following command. (You'll use the kid value in Step 3.)

az keyvault key create --kty RSA-HSM --size 4096 --name KEKforBYOK --ops import --hsm-name <hsm-name>

Step 2: Download the KEK public key

Use az keyvault key download to download the KEK public key to a .pem file. The target key you import is encrypted by using the KEK public key.

az keyvault key download --name KEKforBYOK --hsm-name <hsm-name> --file KEKforBYOK.publickey.pem

Transfer the KEKforBYOK.publickey.pem file to your offline computer. You need this file in the next step.

Step 3: Generate and prepare your key for transfer

To download and install the BYOK tool, see your HSM vendor's documentation. Follow the instructions from your HSM vendor to generate a target key, and then create a key transfer package (a BYOK file). The BYOK tool uses the kid from Step 1 and the KEKforBYOK.publickey.pem file you downloaded in Step 2 to generate an encrypted target key in a BYOK file.

Transfer the BYOK file to your connected computer.

Step 4: Transfer your key to Managed HSM

To complete the key import, transfer the key transfer package (a BYOK file) from your disconnected computer to the internet-connected computer. Use the az keyvault key import command to upload the BYOK file to the Managed HSM.

az keyvault key import --hsm-name <hsm-name> --name <key-name> --byok-file KeyTransferPackage-<key-name>.byok

If the upload is successful, Azure CLI displays the properties of the imported key.

Next steps

You can now use this HSM-protected key in your Managed HSM. For more information, see this price and feature comparison.