Security in Wireless Sensor Networks - Security for Wireless Sensor Networks Using Identity-Based Cryptography - page 30

• Integrity: The goal of integrity is to affirm that the data received is not altered by an
interceptor during communication (by insertion, deletion, or replay of data) and
is exactly as it was sent by the authorized sender. Usually, cryptographic methods
such as digital signatures and hash values are used to provide data integrity.
• Confidentiality: The goal of confidentiality is to protect the data from unauthor-
ized disclosure. A common approach to achieving confidentiality is by encrypt-
ing user data.
• Availability: The goal of availability is to ensure that the system (network)
resources are available and usable by an authorized entity, upon its request. It
tries to achieve survivability of the network at all times.
• Access control: The goa l of access control is to enforce access rights to a ll resources
in its system. It tries to prevent unauthorized use of system and network
resources. Access control is closely related to authentication attributes. It plays
a major role in preventing leakage of information during a node-compromise
attack. One of the conventional approaches to access control is to use threshold
cryptography. This approach hides data by splitting it into a number of shares.
To retrieve the final data, each share should be received through an authenti-
cated process.
• Nonrepudiation: Nonrepudiation can be best explained with an example. Let
Alice and Bob be two nodes, who wish to communicate with each other. Let
Alice send a message (M) to Bob. Later, Alice claims that she did not send any
message to Bob. Hence, the question that arises is how Bob should be protected
if Alice denies any involvement in any form of communication with Bob. Non-
repudiation aims to achieve protection against communicating entities that deny
that they ever participated in any sort of communication with the victim.
2.3.1 Security in WSN Using a Layered Approach
2.3.1.1 Security Measures in the Physical Layer
To prevent radio interference or jamming, the two common techniques used are
frequency-hopping spread spectrum (FHSS) and direct-sequence spread spectrum
(DSSS). In FHSS, the signal is modulated at frequencies such that it hops from one fre-
quency to another in a random fashion at a fixed time interval. The transmitter and the
corresponding receiver hop between frequencies using the same pseudo-random code
for modulation and demodulation. If an eavesdropper intercepts a FHSS signal, unless
he has prior knowledge of the spreading signal code, he will not be able to demodulate
the signal. Furthermore, spreading the signal across multiple frequencies will consider-
ably reduce interference.
In DSSS, a spreading code is used to map each data bit in the original signal to mul-
tiple bits in the transmitted signal. The pseudo-random code (spreading code) spreads
the input data across a wider frequency range compared to the input frequency. In the
frequency domain, the output signals appear as noise. Since the pseudo-random code
provides a wide bandwidth to the input data, it allows the signal power to drop down