Wireless Sensor Networks: Security Requirements - Authentication, Integrity, and Freshness
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As in conventional systems, authentication techniques verify the identity of the participants in a communication, distinguishing in this way legitimate users from intruders.
In the case of sensor networks, it is essential for each sensor node and base station to have the ability to verify that the data received was really send by a trusted sender and not by an adversary that tricked legitimate nodes into accepting false data. If such a case happens and false data are supplied into the network, then the behavior of the network could not be predicted and most of times will not outcome as expected.
Authentication objective is essential to be achieved when clustering of nodes is performed. I remind you that clustering involves grouping nodes based on some attribute such as their location, sensing data etc and that each cluster usually has a cluster head that is the node that joins its cluster with the rest of the sensor network (meaning that the communication among different clusters is performed through the cluster heads). In these cases, where clustering is required, there are two authentication situations which should be investigated; first it is critical to ensure that the nodes contained in each cluster will exchange data only with the authorized nodes contained and which are trusted by the specified cluster (based on some authentication protocol). Otherwise, if nodes within a cluster receive data from nodes that are not trusted within the current community of nodes and further process it, then the expected data from that cluster will be based on false data and may cause damage. The second authentication situation involves the communication between the cluster heads of each cluster; communication must be established only with cluster heads that can prove their identity. No malicious node should be able to masquerade as a cluster head and communicate with a legitimate cluster head, sending it false data or either compromising exchanged data.
Moving on to the integrity objective, there is the danger that information could be altered when exchanged over insecure networks. Lack of integrity could result in many problems since the consequences of using inaccurate information could be disastrous, for example for the healthcare sector where lives are endangered.
Integrity controls must be implemented to ensure that information will not be altered in any unexpected way. Many sensor applications such as pollution and healthcare monitoring rely on the integrity of the information to function with accurate outcomes; it is unacceptable to measure the magnitude of the pollution caused by chemicals waste and find out later on that the information provided was improperly altered by the factory that was located near by the monitored lake. Therefore, there is urgent need to make sure that information is traveling from one end to the other without being intercepted and modified in the process.
One of the many attacks launched against sensor networks is the message replay attack where an adversary may capture messages exchanged between nodes and replay them later to cause confusion to the network. Data freshness objective ensures that messages are fresh, meaning that they obey in a message ordering and have not been reused. To achieve freshness, network protocols must be designed in a way to identify duplicate packets and discard them preventing potential mix-up.
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