Thanks for the links! I was very interested to see Thomas’s slides on OpenWSN “fresh” . It would be valuable to have a 6TiSCH implementation in RIOT. Are there any more details available on this project?
there used to be OpenWSN support in RIOT but due to a missing maintainer on our side (we did not find the time to adapt it to our rapidly changing APIs for timers and networking) we had to remove it for now .
this is planned for the summer. We discussed with Thomas, and the rough plan was to propose this topic for the IETF hackathon  in Prague this summer, whereby some RIOTers and some OpenWSN people would attend and hammer it out. Until then, OpenWSN Fresh is getting ready AFAIK.
I would like to let you know about our recent work  on access control for the IoT. You can find a pdf version of this work here  and a reference RIOT-based implementation here 
The basic idea is that a trusted third party helps a Thing and an *authorized* user to establish an ephemeral (session-specific) encryption key. It is lightweight (in uses only HMAC and AES) and it provides Thing authentication.