Request-response over pub/sub for openC2

Openc2 members,

I received a request for technical assistance on openc2 over mqtt spec from Mr Brule earlier today. I am responding to oasis relay as recommended by Mr Brule.

The discussion is around setting up topics.

> Would you set up a topic that is 'action' so an orchestrator would

> post a 'deny evil_domain' then would you set up another topic 'response_action'

> so any actuator that could act on the deny evil domain would post

> its ack on the 'response_deny' channel? Or would you guys make the

>topics more device centric, so there would be a topic that is 'gateway_routers'

> and the orchestrator posts the commands there then each

> router would have its own topic 'router_one', 'router_two' etc. to post its response.

There are a few challenges to the openc2 spec in terms of pub sub. Openc2 messaging specifies request-response semantics, which is a different message pattern vis-Ã-vis pub-sub. The way we may manage req-res over pub-sub is as below (as implemented in McAfee opendxl )

An orchestrator / publisher who intends to receive a response shall subscribe to a an arbitrary topic of its choice. We simply call this the response topic, and it is like the publishers callback phone number. Normally you want this callback topic to be statistically unique, and a guid works well.
The publisher embeds this response topic in the message so that the subscriber / actuator can publish the response back to the callback topic.
The actuator / subscriber topics are better named after the actions rather than the device. Device characteristics are generally unbounded, and you see a topic sprawl with a device centric topic naming as compared to a capability centric topic naming. Also, capabilities centric naming has other benefits like creating a topic hierarchy that automatically describes a hierarchy of actions.

Happy to discuss further on the thread

Sudeep Das

Principal Engineer

McAfee LLC

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