  Billions of smart, but constrained objects wirelessly connected to the global
network require novel paradigms in network design. New protocol standards,
tailored to constrained devices, have been designed taking into account
requirements such as asynchronous application traffic, need for caching, and
group communication. The existing connection oriented security architecture is
not able to keep up---first, in terms of the supported features, but also in
terms of the scale and resulting latency on small constrained devices. In this
paper, we propose an architecture that leverages the security concepts both
from content-centric and traditional connection-oriented approaches. We rely on
secure channels established by means of (D)TLS for key exchange, but we get rid
of the notion of the 'state' among communicating entities. We provide a
mechanism to protect from replay attacks by coupling our scheme with the CoAP
application protocol. Our object-based security architecture (OSCAR)
intrinsically supports caching and multicast, and does not affect the radio
duty-cycling operation of constrained objects. We evaluate OSCAR in two cases:
802.15.4 Low Power and Lossy Networks (LLN) and Machine-to-Machine (M2M)
communication for two different hardware platforms and MAC layers on a real
testbed and using the Cooja emulator. We show significant energy savings at
constrained servers and reasonable delays. We also discuss the applicability of
OSCAR to Smart City deployments.
