Keystone

Security compliance

The keystone charm’s password-security-compliance configuration option sets the [security_compliance] section of Keystone’s configuration file. The value of this option is a YAML dictionary that includes support for the following keys (value formats and units are also included).

change_password_upon_first_use: <boolean>
disable_user_account_days_inactive: <int> (days)
lockout_duration: <int> (seconds)
lockout_failure_attempts: <int>
minimum_password_age: <int> (days)
password_expires_days: <int> (days)
password_regex: <string>
password_regex_description: <string>
unique_last_password_count: <int>

Important

The upstream document Security compliance and PCI-DSS should be consulted before setting any of these options.

The configuration is typically contained within a file, say config.yaml. For example:

password-security-compliance:
   change_password_upon_first_use: True
   lockout_duration: 1800
   lockout_failure_attempts: 3
   ...

It is applied in the usual way:

juju config keystone --file config.yaml

The charm will protect service accounts (accounts requested by other units that are in the service domain) against being forced to change their password. Operators should also ensure that any other accounts are protected as per the above referenced note.

Operators should also ensure that any non-service accounts are protected as per the upstream document.

The charm will enter a blocked state if the value of charm option password-security-compliance is not in valid YAML format and/or the individual service options do not conform to the proper value formats.

Token support

Over time OpenStack has come to support two Keystone token formats: UUID and Fernet.

Fernet tokens were added to address the issue of size observed with PKI and PKIZ tokens in addition to continuing the Keystone behaviour of persisting tokens to a common database cluster (like UUID tokens). For more information see this Fernet FAQ.

Important

Starting with OpenStack Rocky, only the Fernet format for authentication tokens is supported. This is documented as a known upgrade issue.

Fernet keys

Theory of operation

Keystone generates Fernet keys, which in turn are used to generate/encrypt and decode/decrypt Fernet tokens.

There are three key types, and each is associated with a naming scheme that is applied to the directories in which they are found. Directory names are based on integers:

  • primary key

    • integer: the highest one

    • generates tokens

    • number of keys: one

  • staged key

    • integer: ‘0’

    • will become the next primary key

    • can decode tokens

    • number of keys: one

  • secondary key

    • integer: any other number

    • was previously a primary key

    • can decode tokens

    • number of keys: one or more

Each key type must be present at all times. This means Keystone uses a minimum of three keys.

Key rotation

Key rotation refers to the process by which two keys assume a different type, one key gets created, and typically one key gets removed:

  1. staged → primary

  2. primary → secondary

  3. the staged is created

  4. a secondary is removed

A key will get removed if the total number of keys surpasses the specified maximum allowed (more on this later).

This process takes place on the master keystone unit and takes into account three aspects:

  • rotation frequency

  • token expiration

  • maximum number of active keys

These are related according to this formula:

\[max\_active\_keys = \frac{ token\_expiration }{ rotation\_frequency } + 2\]

In the keystone charm, token expiration and the maximum number of active keys are specified, respectively, with the token-expiration and the fernet-max-active-keys configuration options.

For example, given that an administrator desires a token expiration of 1 hour (3600 seconds) and a rotation frequency of 15 minutes (900 seconds), the maximum number of active keys must be six:

\[\begin{split}\begin{eqnarray} max\_active\_keys &=& \frac{ 3600 }{ 900 } + 2\\ &=& 4+2\\ &=& 6\\ \end{eqnarray}\end{split}\]

The above two options can then be set accordingly:

token-expiration: 3600
fernet-max-active-keys: 6

Rotation frequency

From the point of view of rotation frequency:

\[rotation\_frequency = \frac{ token\_expiration }{ max\_active\_keys - 2 }\]

Since the denominator must lead to a positive real number for rotation frequency the value of fernet-max-active-keys must be at least three, and this constraint is enforced by the charm.

To increase rotation frequency either decrease fernet-max-active-keys or increase token-expiration. To decrease rotation frequency, do the opposite.

The most notable effect of increasing rotation frequency is the reduction in key lifetime (secondary keys get removed more often).

Default values

These are the default values for these keystone charm options and the resulting default rotation frequency:

  • token-expiration: 3600 sec (1 hour)

  • fernet-max-active-keys: 3

  • rotation frequency: 3600 sec (1 hour)

Token validation breakage

Token validation breakage is a situation in which a decoding key is no longer available to validate an unexpired token. This can be caused by a rotation frequency that has been set too high (a very short key lifetime) or by keys failing to synchronise (from the master keystone unit to the other units) prior to the succeeding rotation. Incremental changes to rotation frequency is therefore advised.