  The increasing importance and consequent challenges of establishing indirect
trusted relationships in highly dynamic social networks such as vehicular
social networks (VSNs), are investigated in this paper. VSNs are mobile social
networks that aim to create social links among travellers on the roads. Besides
matching interests between two users, social trust is essential to successfully
establish and nurture a social relationship. However, the unique
characteristics of VSNs pose many challenges such as uncertainty, subjectivity
and intransitivity to indirect social trust modelling. Furthermore, the current
trust models in the literature inadequately address trust propagation in VSNs.
We propose a novel indirect social trust model for VSNs using evolving graph
theory and the Paillier cryptosystem. We consider the VSN as a highly dynamic
social evolving graph where social ties among vehicles hold a trustworthiness
factor that evolves over time. This factor is estimated based on the
behaviours, opinions, distances, and communication metrics of the parties
involved. Employing the homomorphic property of the Paillier cryptosystem, the
proposed model targets the subjectivity problem when combining multiple
opinions to establish an indirect trusted relationship. Through analysis of
computational and communication complexities, we show the viability of the
proposed model and the efficiency of its indirect trust computation algorithm.
