HSM integration - seal wrap

Vault Enterprise integrates with Hardware Security Module (HSM) platforms to opt-in automatic unsealing. HSM integration provides three pieces of special functionality:

• Root Key Wrapping: Vault protects its root key (previously known as master key) by transiting it through the HSM for encryption rather than splitting into key shares
• Automatic Unsealing: Vault stores its encrypted root key in storage, allowing for automatic unsealing
• Seal Wrapping to provide FIPS KeyStorage-conforming functionality for Critical Security Parameters

In some large organizations, there is a fair amount of complexity in designating key officers, who might be available to unseal Vault installations as the most common pattern is to deploy Vault immutably. As such automating unseal using an HSM provides a simplified yet secure way of unsealing Vault nodes as they get deployed.

Vault pulls its encrypted root key from storage and transit it through the HSM for decryption via PKCS #11 API. Once the root key is decrypted, Vault uses the root key to decrypt the encryption key to resume with Vault operations.

Challenge

The Federal Information Processing Standard (FIPS) 140-2 is a U.S. Government computer security standard used to accredit cryptography modules. If your product or service does not follow FIPS' security requirements, it may complicate your ability to operate with U.S. Government data.

Aside from doing business with U.S. government, your organization may care about FIPS which approves various cryptographic ciphers for hashing, signature, key exchange, and encryption for security.

Solution

Integrate Vault with FIPS 140-2 certified HSM and enable the Seal Wrap feature to protect your data.

Vault encrypts secrets using 256-bit AES in GCM mode with a randomly generated nonce prior to writing them to its persistent storage. By enabling seal wrap, Vault wraps your secrets with an extra layer of encryption leveraging the HSM encryption and decryption.

Benefits of the Seal Wrap:

• Conformance with FIPS 140-2 directives on Key Storage and Key Transport as certified by Leidos
• Supports FIPS level of security equal to HSM
  • For example, if you use Level 3 hardware encryption on an HSM, Vault will be using FIPS 140-2 Level 3 cryptography
• Allows Vault to be deployed in high security GRC environments (e.g. PCI-DSS, HIPAA) where FIPS guidelines important for external audits
• Pathway for Vault's use in managing Department of Defense's (DOD) or North Atlantic Treaty Organization (NATO) military secrets

Prerequisites

This intermediate operations tutorial assumes that you have:

• A supported HSM cluster to integrate with Vault
• Vault Enterprise version 0.9.0 or later

Step 1: Configure HSM Auto-unseal

When a Vault server is started, it normally starts in a sealed state where a quorum of existing unseal keys is required to unseal it. By integrating Vault with HSM, your Vault server can be automatically unsealed by the trusted HSM key provider.

1. To integrate your Vault Enterprise server with an HSM cluster, the configuration file must define the PKCS11 seal stanza providing necessary connection information.

   Example: config-hsm.hcl

   # Provide your AWS CloudHSM cluster connection information
   seal "pkcs11" {
     lib = "/opt/cloudhsm/lib/libcloudhsm_pkcs11.so"
     slot = "1"
     pin = "vault:Password1"
     key_label = "hsm_demo"
     hmac_key_label = "hsm_hmac_demo"
     generate_key = "true"
   }
   
   # Configure the storage backend for Vault
   storage "file" {
     path = "/tmp/vault"
   }
   
   # Addresses and ports on which Vault will respond to requests
   listener "tcp" {
     address          = "0.0.0.0:8200"
     tls_disable      = "true"
   }
   
   ui = true
   disable_mlock = true
   

   For the purpose of this tutorial, the storage backend is set to the local file system (/tmp/vault) to make the verification step easy.

   Warning

   Although the listener stanza disables TLS (tls_disable = "true") for this tutorial, Vault should always be used with TLS in production to provide secure communication between clients and the Vault server. It requires a certificate file and key file on each Vault host.

   The example configuration defines the following in its seal stanza:

   Parameter	Description
   lib	Path to the PKCS #11 library on the virtual machine where Vault Enterprise is installed.
   slot	The slot number to use.
   pin	PKCS #11 PIN for login.
   key_label	Defines the label of the key you want to use.
   hmac_key_label	Defines the label of the key you want to use for HMACing.
   generate_key	If no existing key with the label specified by key_label can be found at Vault initialization time, Vault generates a key.

   IMPORTANT: Having Vault generate its own key is the easiest way to get up and running, but for security, Vault marks the key as non-exportable. If your HSM key backup strategy requires the key to be exportable, you should generate the key yourself. Refer to the key generation attributes.

   For the full list of configuration parameters, refer to the documentation.

2. If you are using systemd, the ExecStart parameter should point to the correct location of your configuration file. For example, if your configuration file is located at /etc/vault.d/config-hsm.hcl, the vault.service file may look as follow.

   Example: /etc/systemd/system/vault.service

   [Unit]
   Description="HashiCorp Vault - A tool for managing secrets"
   Documentation=https://www.vaultproject.io/docs/
   Requires=network-online.target
   After=network-online.target
   ConditionFileNotEmpty=/etc/vault.d/vault.hcl
   StartLimitIntervalSec=60
   StartLimitBurst=3
   
   [Service]
   User=vault
   Group=vault
   ProtectSystem=full
   ProtectHome=read-only
   PrivateTmp=yes
   PrivateDevices=yes
   SecureBits=keep-caps
   AmbientCapabilities=CAP_IPC_LOCK
   Capabilities=CAP_IPC_LOCK+ep
   CapabilityBoundingSet=CAP_SYSLOG CAP_IPC_LOCK
   NoNewPrivileges=yes
   ExecStart=/usr/local/bin/vault server -config=/etc/vault.d/config-hsm.hcl
   ExecReload=/bin/kill --signal HUP $MAINPID
   KillMode=process
   KillSignal=SIGINT
   Restart=on-failure
   RestartSec=5
   TimeoutStopSec=30
   StartLimitInterval=60
   StartLimitIntervalSec=60
   StartLimitBurst=3
   LimitNOFILE=65536
   LimitMEMLOCK=infinity
   
   [Install]
   WantedBy=multi-user.target
   

3. Start the Vault server.

   Example:

   If starting from the command:

   $ vault server -config=/etc/vault.d/config-hsm.hcl
   

   If starting as a service using systemd, first enable the vault service.

   $ sudo systemctl enable vault
   

   Start the Vault server as a service.

   $ sudo systemctl start vault
   

4. Check the Vault status.

   $ vault status
   
   Key                      Value
   ---                      -----
   Recovery Seal Type       pkcs11
   Initialized              false
   Sealed                   true
   ...
   

5. Initialize Vault.

   First, set the VAULT_ADDR environment variable.

   $ export VAULT_ADDR="http://127.0.0.1:8200"
   

   Initialize Vault.

   $ vault operator init
   

   Example output:

   Recovery Key 1: iz1XWxe4CM+wrOGqRCx8ex8kB2XvGJEdfjhXFC+MA6Rc
   Recovery Key 2: rKZETr6IAy686IxfO3ZBKXPDAOkkwkpSepIME+bjeUT7
   Recovery Key 3: 4XA/KJqFOm+jzbBkKQuRVePEYPrQe3H3TmFVmdlUjRFv
   Recovery Key 4: lfnaYoZufP0uhooO3mHDAKGNZB5HLP9HYYb+LAfKkUmd
   Recovery Key 5: L169hHj3DMpphGsOnS8TEz3Febvdx3vsG3Xr8kGWdUtW
   
   Initial Root Token: s.AWnDagUkKNNbvkENiL72wysn
   
   Success! Vault is initialized
   
   Recovery key initialized with 5 key shares and a key threshold of 3. Please
   securely distribute the key shares printed above.
   

   When Vault is initialized while using an HSM, rather than unseal keys being returned to the operator, recovery keys are returned. These are generated from an internal recovery key that is split via Shamir's Secret Sharing, similar to Vault's treatment of unseal keys when running without an HSM. Some Vault operations such as generation of a root token require these recovery keys.

6. Check the Vault status again.

   $ vault status
   
   Key                      Value
   ---                      -----
   Recovery Seal Type       shamir
   Initialized              true
   Sealed                   false
   Total Recovery Shares    1
   Threshold                1
   Version                  1.2.3+ent.hsm
   Cluster Name             vault-cluster-dfcace02
   Cluster ID               0fe5ab51-ff92-fdb0-9c37-f739679554f8
   HA Enabled               false
   

   Vault is now unsealed (Sealed value is now false).

7. To verify auto-unseal, stop and restart the Vault server and check its status.

   If starting the Vault server as a service using systemd:

   $ sudo systemctl restart vault
   

   Verify the Vault server status.

   $ vault status
   Key                      Value
   ---                      -----
   Recovery Seal Type       shamir
   Initialized              true
   Sealed                   false
   ...
   

Step 2: Enable Seal Wrap

For some values, seal wrapping is always enabled including the recovery key, any stored key shares, the root key, the keyring, and more. When working with the key/value secrets engine, you can enable seal wrap to wrap all data.

Step 3: Test the Seal Wrap Feature

In this step, you are going to:

1. Write some test data
2. View the encrypted secrets

View the encrypted secrets

Remember that the Vault server was configured to use the local file system (/tmp/vault) as its storage backend in this example.

# Configure the storage backend for Vault
storage "file" {
  path = "/tmp/vault"
}

SSH into the machine where the Vault server is running, and check the stored values in the /tmp/vault directory.

$ cd /tmp/vault/logical

Under the /tmp/vault/logical directory, there are two sub-directories. One maps to kv-unwrapped/ and another maps to kv-seal-wrapped/ although you cannot tell by the folder names.

View the secret at rest. One of the directory maps to kv-unwrapped/unwrapped.

Example:

$ cd 2da357cd-55f2-7eed-c46e-c477b70bed18

View its content - password value is encrypted.

$ cat _unwrapped
{"Value":"AAAAAQICk547prhuhMiBXLq2lx8ZkMpSB3p+GKHAwuMhKrZGSeqsFevMS6YoqTVlbvpU9B4zWPZ2HA
SeNZ3YMw=="}

Another directory maps to kv-seal-wrapped/wrapped.

$ cd ../5bcea44d-28a3-87af-393b-c6d398fe41d8

View its content. The password value is encrypted.

$ cat _wrapped
{"Value":"ClBAg9oN7zBBaDBZcsilDAyGkL7soPe7vBA5+ADADuyzo8GuHZHb9UFN2nF1h0OpKEgCIkG3JNHcXt
tZqCi6szcuNBgF3pwhWGwB4FREM3b5CRIQYK7239Q92gRGrcBBeZD6ghogEtSBDmZJBahk7n4lIYF3X4iBqmwZgH
Vo4lzWur7rzncgASofCIIhENEEGghoc21fZGVtbyINaHNtX2htYWNfZGVtb3M="}

Secrets are encrypted regardless; however, the seal-wrapped value is significantly longer despite the fact that both values are the same, my-long-password.

Help and Reference

• HashiCorp + AWS: Integrating CloudHSM with Vault Enterprise webinar
• Seal Wrap documentation
• Vault Configuration - pkcs11 Seal
• Vault Enterprise HSM Support
• NIST SC-12: Cryptographic Key Establishment and Management
• NIST SC-13: Cryptographic Protection