Note: This feature requires Vault Enterprise with the Governance & Policy Module.
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 (HSMs) or Vault Pro (AWS KMS). 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
master 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).
FIPS 140-2 Compliance
Vault's Seal Wrap feature has been evaluated by Leidos for compliance with FIPS 140-2 requirements. When used with a FIPS 140-2-compliant HSM, Vault will store Critical Security Parameters (CSPs) in a manner that is compliant with KeyStorage and KeyTransit requirements. This is on by default for many parts of Vault and opt-in for each individual mount; see the Activating Seal Wrapping section below for details.
Updates Since The Latest FIPS Compliance Audit
The following are values that take advantage of seal wrapping in the current release of Vault that have not yet been asserted as compliant by Leidos. The mechanism for seal wrapping is the same, they simply were not specifically evaluated by the auditors.
- Root tokens
- Replication secondary activation tokens
- Client authentication information for the GCP Auth Backend
- Client authentication information for the Kubernetes Auth Backend
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 master 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. If no specific CSPs are identifiable, all data for the backend may be seal-wrapped.
To see the current list of seal-wrapped data per backend type, see the latest audit letter and updates in the FIPS 140-2 Compliance section above.
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.
Because of the level of flexibility targeted for replication, values sent over replication connections do not currently meet KeyTransit requirements for FIPS 140-2. Vault's clustering implementation does support best practices guidance given in FIPS 140-2, but the cryptographic implementation of TLS is not FIPS 140-2 certified. We may look into providing certified TLS in the future for replication traffic; in the meantime, a transparent TCP proxy that supports certified FIPS 140-2 TLS (such as stunnel) can be used for replication traffic if meeting KeyTransit requirements for replication is necessary.