Rekeying & Rotating Vault

» Background

In order to prevent no one person from having complete access to the system, Vault employs Shamir's Secret Sharing Algorithm. Under this process, a secret is divided into a subset of parts such that a subset of those parts are needed to reconstruct the original secret. Vault makes heavy use of this algorithm as part of the unsealing process.

When a Vault server is first initialized, Vault generates a master key and immediately splits this master key into a series of key shares following Shamir's Secret Sharing Algorithm. Vault never stores the master key, therefore, the only way to retrieve the master key is to have a quorum of unseal keys re-generate it.

The master key is used to decrypt the underlying encryption key. Vault uses the encryption key to encrypt data at rest in a storage backend like the filesystem or Consul.

Typically each of these key shares is distributed to trusted parties in the organization. These parties must come together to "unseal" the Vault by entering their key share.

Vault Shamir Secret Sharing Algorithm

In some cases, you may want to re-generate the master key and key shares. Here are a few examples:

  • Someone joins or leaves the organization
  • Security wants to change the number of shares or threshold of shares
  • Compliance mandates the master key be rotated at a regular interval

In addition to rekeying the master key, there may be an independent desire to rotate the underlying encryption key Vault uses to encrypt data at rest.

Vault Rekey vs Rotate

In Vault, rekeying and rotating are two separate operations. The process for generating a new master key and applying Shamir's algorithm is called "rekeying". The process for generating a new encryption key for Vault to encrypt data at rest is called "rotating".

Both rekeying the Vault and rotating Vault's underlying encryption key are fully online operations. Vault will continue to service requests uninterrupted during either of these processes.

» Rekeying Vault

Rekeying the Vault requires a quorum of unseal keys. Before continuing, you should ensure enough unseal key holders are available to assist with the rekeying to match the threshold configured when the keys were issued.

First, initialize a rekeying operation. The flags represent the newly desired number of keys and threshold:

$ vault operator rekey -init -key-shares=3 -key-threshold=2

This will generate a nonce value and start the rekeying process. All other unseal keys must also provide this nonce value. This nonce value is not a secret, so it is safe to distribute over insecure channels like chat, email, or carrier pigeon.

Key               Value
---               -----
Nonce             dc1aec3b-ae67-5780-b4b5-2a10ca05b17c
Started           true
Rekey Progress    0/1
New Shares        3
New Threshold     2

Each unseal key holder runs the following command and enters their unseal key:

$ vault operator rekey -nonce=<nonce>

Rekey operation nonce: dc1aec3b-ae67-5780-b4b5-2a10ca05b17c
Key (will be hidden):

When the final unseal key holder enters their key, Vault will output the new unseal keys:

Key 1: EDj4NZK6z5Y9rpr+TtihTulfdHvFzXtBYQk36dmBczuQ
Key 2: sCkM1i5BGGNDFk5GsqtVolWRPyd5mWn2eZG0gUySiCF7
Key 3: e5DUvDIH0cPU8Q+hh1KNVkkMc9lliliPVe9u3Fzbzv38

Operation nonce: dc1aec3b-ae67-5780-b4b5-2a10ca05b17c

Vault rekeyed with 3 keys and a key threshold of 2. Please
securely distribute the above keys. When the vault is re-sealed,
restarted, or stopped, you must provide at least 2 of these keys
to unseal it again.

Vault does not store the master key. Without at least 2 keys,
your vault will remain permanently sealed.

Like the initialization process, Vault supports PGP encrypting the resulting unseal keys and creating backup encryption keys for disaster recovery.

» Rotating the Encryption Key

Unlike rekeying the Vault, rotating Vault's encryption key does not require a quorum of unseal keys. Anyone with the proper permissions in Vault can perform the encryption key rotation.

To trigger a key rotation, execute the command:

$ vault operator rotate

This will output the key version and installation time:

Key Term: 2
Installation Time: ...

This will add a new key to the keyring. All new values written to the storage backend will be encrypted with this new key.