Update X-Protocol Interworking Use Case with Security and Privacy Considerations

[mmccool]

Want to assign OliverPfaff to this, github won't let me... to fix. https://github.com/w3c/wot-architecture/blob/master/USE-CASES/X-Protocol%20Interworking.md

[OliverPfaff]

Here I am

[OliverPfaff]

Link correction: https://github.com/w3c/wot-architecture/blob/master/USE-CASES/X-Protocol-Interworking.md

Comments (independent from security&privacy):

• The notion "device" is not welcome by all with stakes in the considered scenario => consider to make namespaces more explicit (OT also has non-devices "devices" that are important) or consider a more generic term that does not clash
• The notion "interoperability" is difficult as well (valid on macro-level where one "device" implements components in multiple stacks e.g. OPC-UA and PROFINET, potentially misleading on micro-level which considers components belonging to one stack e.g. OPC-UA and PROFINET are non-interoperable like HTTP and SMTP are [but computers implementing HTTP and SMTP components may interact])

Comments (re security&privacy): I think the use case needs some more clarification/refinement in order to suggest a (meaningful) proposal for a security&privacy section. For that reason I leave it for the moment with some early input:

• If two (or more) non-interoperable protocols are used in an information exchange between two (or more) endpoints (think of HTTP for the first mile and SMTP behind that) then: -- There is no E2E security/privacy between these endpoints - on protocol level i.e. layers 2..7a -- If there is E2E security/privacy on the level of application data objects depends - on many things such as info representation, encapsulation strategy, key management...
• Intermediaries are an obstacle to security&privacy that can be achieved. Whether and to which extend depends on their nature (protocol gateway, proxy, router, switch...) as well as security mechanisms, for instance: -- S/MIME can traverse protocol gateways, proxies, routers, switches (but not/hardly language boundaries) -- HTTP-over-TLS can traverse switches, routers, proxies but not protocol gateways -- IPsec can traverse routers and switches but not proxies and protocol gateways -- MACsec can not traverse anything (including switches)