Routing in Wireless Sensor Networks Using Identity-Based Cryptography - Security for Wireless Sensor Networks Using Identity-Based Cryptography - page 141

• The deployed sensor nodes are aware of their energy levels. In addition, the nodes
also have the capacity to gauge the energy levels of its immediate neighbors.
• A query-based sensing mechanism is used for information retrieval, and the
information needed is an attribute of a given geographical area.
SCEAR can be categorized into three phases, namely, initialization, identification, and
secure communication.
Initialization:
Each node in the network is preloaded with an energy-aware algorithm that helps in
self-organizing themselves in each cluster (Chan and Perrig 2004). With the intention
of forming a cluster, the elected cluster head broadcasts its identity along with its cur-
rent status. Depending on the signal strength of the broadcasted message, the nodes in
the network decide whether to join the network. The decision to join is dependent on
the principle that the greater the strength of the received signal, the lesser is the energy
required in sending a message to its cluster head. The interested nodes acknowledge
the broadcasted message by sending their identities to their respective cluster heads. For
purposes of confidentiality, the node's identity is encrypted with the cluster head's pub-
lic key (identity of the cluster head). On forming the cluster, each cluster head generates
unique symmetric session keys using the RC5 algorithm and sends it to each of its
members in the cluster (Rivest 1995). The session key is encrypted using the ordinary
node's identity to prevent eavesdropping attacks. Furthermore, the expiration period of
the session key is equal to the lifespan of the elected cluster head.
Identification:
The moment the cluster heads broadcast their identities (discussed in the Initialization
phase), the sink nodes closest to the cluster heads also receive this broadcasted mes-
sage. The sink node responds to this broadcasted message by sending its identity and
location information to the nearest cluster head. The identity and location information
is always sent through a secure channel by encrypting it using the cluster head's iden-
tity. Any pairing- or non-pairing-based identity-based encryption (IBE) algorithm is
used for encrypting this information. The neighboring cluster heads then forward this
information to their immediate neighbors using the same IBE scheme, and the process
continues until all the cluster heads in the network are aware of the sink's identity and
location information.
Secure communication:
Energy conservation has been the prime requirement of a sensor network, and to adhere
to this requirement, SCEAR adopts an event- or query-based sensing functionality. In
addition, SCEAR adopts a hierarchical architecture wherein the ordinary sensor nodes
encrypt the sensed data with their respective cluster head's public key (identity of the
cluster head) before sending the data to the cluster head. Subsequently, the cluster
heads aggregate the sensed data using a data-centric routing model and forwards it to