  The characteristics of high loss rate, resource constraint, being eager for
good security haven't been fully considered in the existing key establishment
protocols of wireless sensor networks. Analyzing the key establishing problem
from the MAC and physical layers, existing protocols are not practicable enough
due to their overlong agreement packets and single round key establishment. To
mitigate the impact of these problems, a group of design principles for secure
sensor networks has been presented and TinyAKE, an authenticated key transport
protocol based on lightweight certificate, is proposed in this paper. The
security of TinyAKE are proved with the theory of indistinguishability,
meanwhile, the correctness is also proved, the performance is analyzed and
compared with the existing similar protocols. Finally TinyAKE is implemented in
the TinyOS with TinyECC. Our evaluation shows that TinyAKE is a more
practicable and trustable authenticated key establishment protocol than
existing protocols. The experimental result shows that the key transport with
certificate mechanism is feasible in WSNs. Moreover, the simulation results
show that the optimal number of repeated negotiation is one when the secure
connectivity rate of TinyAKE is improved by using the repeated key negotiation.
