In a comment on “Threat Model Thursday: ARM’s Network Camera TMSA”, Dips asks:
Would it been better if they had been more explicit with their graphics ? I am a beginner in Threat Modelling and would have appreciated a detailed diagram denoting the trust boundaries. Do you think it would help? Or it would further complicate?
That’s a great question, and exactly what I hoped for when I thought about a series. The simplest answer is ‘probably!’ More explicit boundaries would be helpful. My second answer is ‘that’s a great exercise!’ Where could the boundaries be placed? What would enforce them there? Where else could you put them? What are the tradeoffs between the two?
My third answer is to re-phrase the question. Rather than asking ‘would it help,’ let’s ask ‘who might be helped by better boundary demarcation’ ‘when would it help them,’ and ‘is this the most productive thing to improve?’ I would love to hear everyone’s perspective.
Lastly, it would be reasonable to expect that Arm might produce a model that depends on the sorts of boundaries that their systems can help protect. It would be really interesting to see a model from a different perspective. If someone draws one or finds one, I’d be happy to look at it for the next article in the series.