Add Transport Cert Reference

Launchpad blueprint: https://blueprints.launchpad.net/barbican/+spec/add-transport-cert-ref

Problem description

Transport keys are used to ensure that the secret is pre-encrypted in such a way that only the client and the back-end store can decrypt the secret.

This is for users which do not trust Barbican, but do trust the back-end secret store. Alternatively, clients that are required by FIPS or Common Criteria (CC) requirements only to use CC certified components may be able to argue for being able to use Barbican if the secrets remain opaque in transit through Barbican to their final storage back-ends.

Currently, the client gets the transport key from Barbican. But if the client does not trust Barbican, this is a potential vulnerability. We need to add the ability for the client to retrieve the transport key from the back-end store directly.

Proposed change

The change here is straightforward. Instead of only returning the transport certificate as a result of the GET /transportkeys/{key_id} call, we will also return a reference to the transport key in the header (TRANSPORT_KEY_URL) This reference will be provided by the plugin, and should be a link to a trusted location where the transport cert could be retrieved. In practice, this would most likely be an HTTPS connection to the backend secret store.

Internally, what this means is that the get_transport_key() method in the secret_store interface would be modified to return a dict containing both the value of the transport key and an external URL. We would use this dict to fill in the contents and header of the response.

As this method already has a None default configuration, this change should not require any changes in existing plugins.

Alternatives

This is a trivial change that makes the transport key story more complete.

Data model impact

None.

REST API impact

A new field will be added to the header in the response to GET /transportkeys/{key_id} as described above.

Security impact

Makes transport keys more secure.

Notifications impact

None.

Other end user impact

The client would need to decide whether to accept the value of the transport cert as returned by Barbican, or to retrieve the value from the provided URL.

Performance Impact

None.

Other deployer impact

None.

Developer impact

None.

Implementation

Assignee(s)

Primary assignee:
alee

Work Items

  1. The server side changes can likely be done in a single CR.
  2. Client side changes.

Dependencies

None.

Testing

Unit and functional tests will need to be written.

Documentation Impact

Docs on transport key use will need to be written and updated.

References

None