Intelligent transportation systems seek to maximize the usage of data generated by the vehicles for road users assistance. Combining vehicular ad hoc network with cloud computing makes it easy for the fixed infrastructures along the roads to collect and analyze safety messages for the benefits of the road users and the transportation authorities. However, security features need to be fully assessed before the adoption of such applications. In this paper, we present a secure vehicle traffic data dissemination and analysis in vehicular cloud computing in which the identity privacy of the vehicles and their generated message is achieved through pseudonym techniques. We use anonymous credential to guarantee the authorization of service demanding vehicles. ID-based signature is applied to assure the authentication of the vehicles for given pseudonyms. The efficient verification of signature on the message and revoked vehicles are achieved through batch verification technique and pseudonymous revocation list, respectively. Traffic estimation methods are applied to mine coarse-grained data collected by road side infrastructures. The merits of the proposed protocol compared to existing ones are shown through extensive simulations.