Protocols for Secure Communication in Wireless Sensor Networks

Chapter 4
Key Establishment
Shared secret keys are a prerequisite for communication that is secured by
cryptographic means with regard to the three “classical” security properties:
confidentiality, integrity, and authentication. In wireless sensor networks, confidentiality
is important if, for example, sensor readings or aggregated data
are regarded as secrets that have to be protected against unauthorized reading.
Integrity and authentication are required for WSNs that operate in critical environments
where the manipulation of data may have harmful consequences.
In communicating systems, cryptographic keys can be established in a variety
of ways, which can be broadly categorized in two classes. The first is
ususally described as key exchange: Two (or more) parties each contribute a
partial key that are combined into the final key. A key exchange protocol solves
the problem of how to efficiently convey the partial key to the other party without
compromising the final key. The second class is usually called key agreement.
Here, it is not necessary that both parties contribute key material. The
final key can be chosen externally (and both parties simply agree to use it), or
it can be assigned by one party to the other. Such a case is sometimes called
key transport.
In identity-based key agreement protocols, the only information that may be
exchanged are the identities of the involved parties. Identities are not equivalent
to keys as they are (often) not randomly chosen, static, and public. Based on
the identities, the shared key is determined. This often involves the use of
additional key material, which can be either (pseudo-)randomly constructed or
could be already present. The latter case is the result of key pre-distribution.
In this chapter, we describe identity-based key agreement protocols for wireless
sensor networks. The properties of such protocols match the resource constraints
of WSNs such that they are advantageous over alternative key agreement
approaches.