Protocols for Secure Communication in Wireless Sensor Networks

2.9. Existing Approaches to Wireless Sensor Network Security 61
in 2.7.4.
2.9.3 Secure Routing
Cryptographic keys, being established through techniques discussed in the previous
subsection, help to ensure secure communication with regard to the confidentiality
and the authenticity of messages. It has to made sure, however,
that messages indeed arrive at their destinations without being misrouted or
dropped.
Ariadne [82] is a route discovery protocol that is able to find routes from a
source to a destination in a multi-hop network and pass them back to the sender.
It is secure in the sense that (1) the hosts authenticate themselves and (2) each
host certifies the previous piece of the path from the source to itself. (3) All
host identities are linked through a hash chain. (4) A basic assumption is an
end-to-end secure link between the source and the destination. (This could be
provided by a pre-arranged secret key between both hosts.)
It is assured that malicious hosts cannot cut nodes off the path or insert
new ones. h0 is the initial value, the authentication code of the initial request
message. This is equivalent to a digitally signed request. Each following host
identity X is appended to the hash chain as hi+1 = H[X,hi] where H is a oneway
function. Destination D can easily verify whether the hash chain matches
the path, since it can reconstruct h0. Requests with mismatching items will be
dropped. Intermediate hosts cannot do this verification step and will forward
also bogus messages.
Ariadne does not prevent a malicious host from getting on the selected path
if it follows the protocol. For example, it could then later drop messages being
sent along the path. On the network layer, this will be noticed as a path failure.
A new path discovery request would be issued by the source. Unless the malicious
node creates a bottleneck between source and destination, a path will be
eventually found that passes by the malicious host.
This protocol is not well-suited for wireless sensor networks for several reasons.
(1) The route request is flooded through the network. This is efficient
only in highly dynamic networks. (2) Source routing, for which the protocol
provides the basis, requires node identifiers in the path to be sent along the
node each time the route is used. This is undesirable overhead. The alternative,
caching routes, would require additional memory in hosts. (3) A secure
channel between source and destination hosts is a prerequisite. This implies
that the identity of the destination is known to the source in advance. In sensor
networks, such close links between hosts (sensor nodes) are not a common