threshold/website/content/docs/concepts/security/data-encryption.mdx

---
layout: docs
page_title: Data Encryption
description: |-
  How Boundary secures data at rest
---

# Data Security in Boundary

Boundary has multiple mechanisms to ensure secure end-to-end behavior of the
system. A key part of this is [support for various Key Management
Systems](/docs/configuration/kms) that protect the base encryption keys used
for various functions. This page describes the various KMS key purposes that
Boundary supports and how they are used within the system.

## The `worker-auth-storage` KMS Key

The `worker-auth-storage` KMS key is used by a [PKI
Worker](/docs/configuration/worker/pki-worker) for storage of authentication
keys. It is optional for PKI workers; if not specified the authentication keys
will not be encrypted on disk. This is not used by KMS workers.

## The `root` KMS Key and Per-Scope KEK/DEKs <sup>OSS Only</sup>

Following best practices of using different encryption keys for different
purposes, Boundary has a number of encryption keys generated within each scope.
Each key further contains versions, which hold the key material used to encrypt
data. You can create new key versions by _rotating_ the keys. A key version
can be destroyed, which will re-encrypt any existing data before destroying the
key material permanently.

The `root` KMS key acts as a KEK (Key Encrypting Key) for the scope-specific
KEKs (also referred to as the scope's `root` key). The scope's `root` KEK
and the various DEKs (Data Encryption Keys) are created when a scope is created.
The DEKs are encrypted with the scope's `root` KEK, and this is in turn
encrypted with the KMS key marked for the `root` purpose.

The current scoped DEKs and their purposes are detailed below:

- `audit`: This is used to encrypt secret values in the event log. For more
  information about the event log, refer to
  [the events config](/docs/configuration/events).

- `database`: This is the general-purpose DEK used to encrypt values within the
  database. Values that are encrypted are those generally considered to be
  secret, such as API keys, third-party tokens, certificate private keys, and so
  on.

- `oidc`: This is used to encrypt OIDC information in cookies and authentication
  requests.

- `oplog`: This is used for encrypting oplog (operation log) values for the
  given scope.

- `tokens`: This is used for encrypting tokens generated by auth methods within
  the given scope.

- `sessions`: This is used as a base key against which to derive
  session-specific encryption keys.

### Key version lifecycle Management

You can control the lifecycles of the per-scope KEK and DEKs via the CLI or
API using the key endpoints under the scopes section. To rotate all the keys
in a scope, use the `rotate-keys` endpoint:

```shell-session
$ boundary scopes rotate-keys -scope-id p_A4jfDjZ9jf
```

This endpoint creates new key versions for all keys in the scope
`p_A4jfDjZ9jf`, and makes these key versions the active key versions for
encrypting new data. The previous key version(s) will continue to be used for
decrypting existing data. You can use the `-rewrap` flag to immediately rewrap
all DEK versions with the new KEK version. Otherwise, the DEK versions remain
encrypted by the prior KEK version from when they were created.

To list all keys in a scope and their versions, use the `list-keys` endpoint:

```shell-session
$ boundary scopes list-keys -scope-id p_A4jfDjZ9jf
```

To destroy a key version, use the `destroy-key-version` endpoint:

```shell-session
$ boundary scopes destroy-key-version -scope-id p_A4jfDjZ9jf -key-version-id kdkv_tr6ZN8opYr
```

The latest key version cannot be destroyed, so if you want to destroy the
latest key version, you will need to call the `rotate-keys` endpoint first,
to create a new set of key versions. The `oplog` purpose key versions also
cannot be destroyed at this time.

Destroying a key version sometimes requires background work before it can be
completed. This is because DEK versions that currently encrypt data
necessitate re-encrypting that data with the latest DEK version for each
purpose before they can be deleted. You can monitor the progress of this
re-encryption job via the `list-key-destruction-jobs` endpoint:

```shell-session
$ boundary scopes list-key-version-destruction-jobs -scope-id p_A4jfDjZ9jf
```

Once the job disappears from this list, the associated key version will have
been destroyed and any existing data will have been re-encrypted.

## The `previous-root` KMS key <sup>OSS Only</sup>

The `previous-root` KMS key is used when migrating to a new `root` key. Adding
the `previous-root` KMS key to your configuration informs the Controller to use
it for decrypting the existing information in the database, allowing you to
rotate and rewrap the KEKs to complete the migration to the new root key.

## The `worker-auth` KMS Key <sup>OSS Only</sup>

The `worker-auth` KMS key is a key shared by the Controller and Worker in order
to authenticate a Worker to the Controller. Specifics of this mechanism can be
found on the [Connections/TLS page](/docs/concepts/security/connections-tls). If
a worker is used with [PKI
authentication](/docs/configuration/worker/pki-worker) this is unnecessary.

## The `recovery` KMS Key <sup>OSS Only</sup>

The `recovery` KMS key is used for rescue/recovery operations that can be used
by a client to authenticate almost any operation within Boundary. Its mechanism
of operation is very similar to the `worker-auth` flow in terms of using a
shared KMS between the client and the Controller for authentication. A nonce and
creation time are included as an encrypted payload, formatted as a token and
sent to the Controller. The time and nonce are used to ensure that a value
cannot be replayed by an adversary, and also to ensure that each operation must
be individually authenticated by a client so that revoking access to the KMS has
an immediate result.

~> **Note:** It is not required for this `kms` configuration block to exist in the
Controller's configuration file. It's best practice to leave it out except when
actually needed, and to use change control capabilities to ensure that the
configuration file modification is authorized. After it's no longer needed, the
block should be removed.

On the client side, a user can use the `-recovery-config` flag with any
operation on the CLI to specify a configuration file containing a suitable `kms`
block. This functionality is also accessible via the Go SDK.

~> **Note:** Requests authorized via this mechanism will show a user of `u_recovery`. This
mechanism _cannot_ be used to authorize a session, as there is no uniquely
identifying user information available.

There are some other situations where this mechanism can be useful. For example,
it is possible to use this mechanism, along with some defaults in the Terraform
provider, to ensure that _everything_ in Boundary is created through Terraform,
with the exception of resources that cannot themselves be deleted. (This
consists of built-in anonymous (`u_anon`), authenticated (`u_auth`), and
recovery (`u_recovery`) users and the `global` scope.). By initializing Boundary
with the options to skip creating default resources, Terraform can be used to
create the specific resources needed instead, with the `recovery` KMS used to
authenticate setting up the initial auth method(s).

## The `config` KMS Key <sup>OSS Only</sup>

This key can be used to encrypt values within Boundary's configuration file. By
sharing this block between Boundary and an operator, the operator can put
sensitive or secret values (such as cloud API keys for KMSes) in Boundary's
configuration file, run `boundary config encrypt` to encrypt the file, and then
safely pass the file to a change control system. Only another operator or system
with access to that KMS can decrypt the values. Boundary will check for a
`config` KMS block on startup, and if it exists, will use it to decrypt any
encrypted values found at startup time.