Note: This feature requires Vault Enterprise Plus.
Vault Enterprise features a mechanism to wrap values with an extra layer of encryption for supporting seals. This adds an extra layer of protection and is useful in some compliance and regulatory environments, including FIPS 140-2 environments.
To use this feature, you must have an active or trial license for Vault Enterprise Plus (HSMs). To start a trial, contact HashiCorp sales.
Seal Wrap is enabled by default on supporting seals. This implies that the seal must be available throughout Vault's runtime. Most cloud-based seals should be quite reliable, but, for instance, if using an HSM in a non-HA setup a connection interruption to the HSM will result in issues with Vault functionality.
To disable seal wrapping, set
disable_sealwrap = true in Vault's
configuration file. This will not affect auto-unsealing functionality; Vault's
root key will still be protected by the seal wrapping mechanism. It will
simply prevent other storage entries within Vault from being seal wrapped.
N.B.: This is a lazy downgrade; as keys are accessed or written their seal wrapping status will change. Similarly, if the flag is removed, it will be a lazy upgrade (which is the case when initially upgrading to a seal wrap-supporting version of Vault).
Activating Seal Wrapping
For some values, seal wrapping is always enabled with a supporting seal. This includes the recovery key, any stored key shares, the root key, the keyring, and more; essentially, any Critical Security Parameter (CSP) within Vault's core. If upgrading from a version of Vault that did not support seal wrapping, the next time these values are read they will be seal-wrapped and stored.
Backend mounts within Vault can also take advantage of seal wrapping. Seal
wrapping can be activated at mount time for a given mount by mounting the
backend with the
seal_wrap configuration value set to
true. (This value
cannot currently be changed later.)
A given backend's author can specify which values should be seal-wrapped by identifying where CSPs are stored. They may also choose to seal wrap all or none of their values.
Note that it is often an order of magnitude or two slower to write to and read from HSMs or remote seals. However, values will be cached in memory un-seal-wrapped (but still encrypted by Vault's built-in cryptographic barrier) in Vault, which will mitigate this for read-heavy workloads.
Seal Wrap and Replication
Seal wrapping takes place below the replication logic. As a result, it is transparent to replication. Replication will convey which values should be seal-wrapped, but it is up to the seal on the local cluster to implement it. In practice, this means that seal wrapping can be used without needing to have the replicated keys on both ends of the connection; each cluster can have distinct keys in an HSM or in KMS.
In addition, it is possible to replicate from a Shamir-protected primary cluster to clusters that use HSMs when seal wrapping is required in downstream datacenters but not in the primary.
Each plugin (whether secret or auth) maintains control over parameters it feels are best to Seal Wrap. These are usually just a few core values as Seal Wrapping does incur some performance overhead.
Some examples of places where seal wrapping is used include:
- The LDAP, RADIUS, Okta, and AWS auth methods, for storing their config.
- PKI for storing the issuers and their keys,
- SSH for storing the CA's keys,
- KMIP for storing managed objects (externally-provided keys) and its CA keys.
- Transit for storing keys and their policy.
See the FIPS-specific Seal Wrap documentation for more information about using Seal Wrapping to achieve FIPS 140-2 compliance. Note that there are additional FIPS considerations regarding Seal Wrap usage and Vault Replication.