  A common approach to securing end-to-end connectivity between devices on the
Internet is to utilise a cloud-based intermediary. With this reliance upon a
third-party comes a set of security and privacy concerns that are difficult to
mitigate. A promising new protocol, Wireguard, dispenses with the middleman to
provide secure peer-to-peer communication. However, support for initial key
exchange falls outside Wireguard's scope, making it potentially vulnerable to
insecure out-of-band key exchange. The design of secure and usable key exchange
methods is challenging, not least in domestic spaces, as they're often
characterised by technically naive users in multi-occupancy environments,
making them susceptible to insider and passer-by attacks (i.e.: theft,
observation attacks, relay and impersonation attacks). We describe and present
the results from a design ideation study that probes the use of tangible,
multi-factor approaches for securing key exchange in domestic spaces. The study
suggests that a home's semi-fixed features (e.g.: lamps, shelves, chairs) can
be instrumented to support a promising three-factor authentication approach
('what you have, what you know and where you are') to enable key exchange
solutions that are i. more secure than commonly used naive approaches and ii.
desirable for end users.
