In fact, a secure key management scheme is the prerequisite for
the security of these primitives, and thus essential to achieving secure infrastructure
in sensor networks.
Due to resource constraints, achieving such key agreement in wireless sensor
networks is non-trivial. The challenge of designing key management protocols
for sensor networks lies in establishing a secure communication infrastructure,
before any routing fabric has been established and either with or
without the presence of any trusted authority or fixed server, from a collection
of sensor nodes which have no prior contact with each other.
Some cryptographic information is normally preloaded in sensor nodes before
deployment, and allows sensor nodes to perform secure communications
with each other. Most schemes do not assume prior knowledge of the network
deployment topology and allow nodes to be added to the network after
deployment. The schemes must be low computational and have low storage
requirements.
There are three types of general key agreement schemes: trusted-server
scheme, self-enforcing scheme, and key pre-distribution scheme. We explain
these schemes in details in the following subsections.
4.1 Trusted-server Scheme
The trusted-server scheme depends on a trusted and secure server such as
the base station for key agreement between nodes, e.g., Kerberos [32]. The
server can be treated as the Key Distribution Center (KDC).
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