Import HSM-protected keys to Key Vault (BYOK)

For added assurance when you use Azure Key Vault, you can import or generate a key in a hardware security module (HSM); the key will never leave the HSM boundary. This scenario often is referred to as bring your own key (BYOK). Key Vault uses the nCipher nShield family of HSMs (FIPS 140-2 Level 2 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 Azure Key Vault.

Note

This functionality is not available for Azure China 21Vianet.

This import method is available only for supported HSMs.

For more information, and for a tutorial to get started using Key Vault (including how to create a key vault for HSM-protected keys), see What is Azure Key Vault?.

Overview

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

  • In Key Vault, 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. Only Key Vault Premium SKU supports RSA-HSM keys.
  • 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 is transferred to the Key Vault HSM. Only the encrypted version of your key leaves the on-premises HSM.
  • A KEK that's generated inside a Key Vault HSM is not exportable. HSMs enforce the rule that no clear version of a KEK exists outside a Key Vault HSM.
  • The KEK must be in the same key vault where the target key will be imported.
  • When the BYOK file is uploaded to Key Vault, a Key Vault HSM uses the KEK private key to decrypt the target key material and import it as an HSM key. This operation happens entirely inside a Key Vault HSM. The target key always remains in the HSM protection boundary.

Prerequisites

The following table lists prerequisites for using BYOK in Azure Key Vault:

Requirement More information
An Azure subscription To create a key vault in Azure Key Vault, you need an Azure subscription. Sign up for a free trial.
A Key Vault Premium SKU to import HSM-protected keys For more information about the service tiers and capabilities in Azure Key Vault, see Key Vault Pricing.
An HSM from the supported HSMs list and a BYOK tool and instructions provided by your HSM vendor You must have permissions for an HSM and basic knowledge of how to use your HSM. See Supported HSMs.
Azure CLI version 2.1.0 or later See Install the Azure CLI.

Supported HSMs

Vendor name Vendor Type Supported HSM models More information
Cryptomathic ISV (Enterprise Key Management System) Multiple HSM brands and models including
  • nCipher
  • Thales
  • Utimaco
See Cryptomathic site for details
Cryptomathic BYOK tool and documentation
Entrust Manufacturer,
HSM as a service
  • nShield family of HSMs
  • nShield as a service
nCipher new BYOK tool and documentation
Fortanix Manufacturer,
HSM as a service
  • Self-Defending Key Management Service (SDKMS)
  • Equinix SmartKey
Exporting SDKMS keys to Cloud Providers for BYOK - Azure Key Vault
IBM Manufacturer IBM 476x, CryptoExpress IBM Enterprise Key Management Foundation
Marvell Manufacturer All LiquidSecurity HSMs with
  • Firmware version 2.0.4 or later
  • Firmware version 3.2 or newer
Marvell BYOK tool and documentation
nCipher Manufacturer,
HSM as a service
  • nShield family of HSMs
  • nShield as a service
nCipher new BYOK tool and documentation
Securosys SA Manufacturer,
HSM as a service
Primus HSM family, Securosys Clouds HSM Primus BYOK tool and documentation
StorMagic ISV (Enterprise Key Management System) Multiple HSM brands and models including
  • Utimaco
  • Thales
  • nCipher
See StorMagic site for details
SvKMS and Azure Key Vault BYOK
Thales Manufacturer
  • Luna HSM 7 family with firmware version 7.3 or newer
Luna BYOK tool and documentation
Utimaco Manufacturer,
HSM as a service
u.trust Anchor, CryptoServer Utimaco BYOK tool and Integration guide

Supported key types

Key name Key type Key size/curve Origin Description
Key Exchange Key (KEK) RSA 2,048-bit
3,072-bit
4,096-bit
Azure Key Vault HSM An HSM-backed RSA key pair generated in Azure Key Vault
Target key
RSA 2,048-bit
3,072-bit
4,096-bit
Vendor HSM The key to be transferred to the Azure Key Vault HSM
EC P-256
P-384
P-521
Vendor HSM The key to be transferred to the Azure Key Vault HSM

Generate and transfer your key to the Key Vault HSM

To generate and transfer your key to a Key Vault HSM:

Step 1: Generate a KEK

A KEK is an RSA key that's generated in a Key Vault HSM. The KEK is used 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 key vault where you intend to import the target key
  • Created with allowed key operations set to import

Note

The KEK must have 'import' as the only allowed key operation. 'import' is mutually exclusive with all other key operations.

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 will use the kid value in Step 3.)

az keyvault key create --kty RSA-HSM --size 4096 --name KEKforBYOK --ops import --vault-name ContosoKeyVaultHSM

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 --vault-name ContosoKeyVaultHSM --file KEKforBYOK.publickey.pem

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

Step 3: Generate and prepare your key for transfer

Refer to your HSM vendor's documentation to download and install the BYOK tool. Follow instructions from your HSM vendor to generate a target key, and then create a key transfer package (a BYOK file). The BYOK tool will use 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.

Note

Importing RSA 1,024-bit keys is not supported. Importing Elliptic Curve key with curve P-256K is not supported.

Known issue: Importing an RSA 4K target key from Luna HSMs is only supported with firmware 7.4.0 or newer.

Step 4: Transfer your key to Azure Key Vault

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 Key Vault HSM.

To import an RSA key use following command. Parameter --kty is optional and defaults to 'RSA-HSM'.

az keyvault key import --vault-name ContosoKeyVaultHSM --name ContosoFirstHSMkey --byok-file KeyTransferPackage-ContosoFirstHSMkey.byok

To import an EC key, you must specify key type and the curve name.

az keyvault key import --vault-name ContosoKeyVaultHSM --name ContosoFirstHSMkey --byok-file --kty EC-HSM --curve-name "P-256" KeyTransferPackage-ContosoFirstHSMkey.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 key vault. For more information, see this price and feature comparison.