Impact of hash value truncation on ID anonymity in Wireless Sensor Networks

Hash functions have been used to address security requirements such as integrity, message authentication and non-repudiation. In WSNs, these functions are also used to preserve sensor nodes’ identity (ID) anonymity, i.e., they are used to generate and verify dynamic pseudonyms that are used to identify sensor nodes in a communication session. In this latter application, there is an open issue as to how long the output of a hash function (i.e. hash value) we should use in pseudonym generation. The longer the hash value, the longer is the pseudonym, thus the harder it is to guess a pseudonym that is generated by using a hash function. On the other hand, the use of a longer hash value also means that the bandwidth and energy costs in transmitting the pseudonym will be higher. As sensor nodes typically have limited resources and are battery powered, the balance between the protection level of ID anonymity and performance and energy costs incurred in providing such a protection is an open issue. This paper investigates the use of hash value truncation in preserving ID anonymity in WSNs and the impact of hash value truncation on four criteria attributes (security against brute force attacks, probability of pseudonym collisions, energy trade-off and end-to-end packet delivery delay). It reports the possible impacts of other factors including the type and usage of hash functions, sensor node capabilities, adversary capabilities, ability to resolve pseudonym collisions, network density and data collection rate. The results show that the impacts of these factors may be contradictory. Therefore, the determination of an optimal level of hash value truncation should consider all trade-offs brought by these factors.