Protocols for Secure Communication in Wireless Sensor Networks

6.2. Basic Interleaved Authentication 161
It has been noted [46] that in many systems, other characteristics than identity
are usually more important to know, such as location or behaviour. For
example, it may be important to know that the device, with which a communication
relationship is being established, is indeed located at a certain place.
However, this information cannot be conveyed by an identifier of the device
alone and must be established through other means. For example, if an interface
based on physical contact, such as a cable plug, can be accessed, proximity
is immediately established. Verifying the location of a remote device is much
harder and usually involves a trusted entity, such as a location beacon [158].
Sometimes, authentication is merely used to ensure integrity. In [42], the
protection of military, large-scale WSN deployments against attacks on their
integrity has been studied. The main objective is to prevent an adversary from
placing a majority of malicious nodes within an area. This ensures that reliable
information (e.g. for surveillance) can be retrieved. For that purpose,
nodes are equipped with batch keys, which correspond to their deployment
area, and diversity keys, which provide uniqueness within a deployment area.
When information is retrieved from a set of nodes, it is made sure that nodes
with duplicate diversity keys or inappropriate batch keys are disregarded. Thus,
cryptographic node authentication servers as a means to ensure the integrity of
application-level data.
In summary, we observe that identity serves an important purpose for message
authentication. However, identity is not as important in WSNs as in other
systems. The reasons are that trustworthiness is not guaranteed solely by a
known identifier, and group membership is more relevant than individual identity.
We thus conclude that integrity protection without individual authentication
is sufficient for many applications. In this chapter, we show how message
integrity protection can be achieved with much less costly means than would
be necessary for end-to-end authentication.
6.2 Basic Interleaved Authentication
In the following authentication scheme, messages are authenticated not endto-end,
i.e. between the source and the sink, but locally, i.e. only between
intermediate nodes within a small hop distance. Thereby, it is unnecessary
to transfer any secret keys or certificates to the sink, while the scheme still
effectively preserves the integrity of messages.