# A Distributed Mix-Context-Based Method for Location Privacy in Road Networks
###### Abstract
The mobile node (vehicle) in a network can broadcast Basic Safety Messages (BSMs), Cooperative Aware Messages (CAM) or beacons to disseminate road environment information. The beacon message's contents consist of vehicle identity, velocity, position, and other information [9]. The vehicle broadcasts beacon messages in plaintext format, and so other entities in the network are able to learn the actual identity and location of vehicles by analyzing these beacon messages. Similarly, an adversary can obtain the personal information of a vehicle driver by collecting beacon messages and tracking the various locations visited, thus coming to know the behavior and activities of the vehicle driver. This has the potential to pose several types of threat to the vehicle driver, such as damage to social reputation, physical harassment, blackmailing, and property loss [10]. To protect the privacy of the vehicle, pseudonyms can be used in place of the real identity in the message, and this is a commonly accepted solution. The pseudonym is an alias or randomized identity of a vehicle inserted in the beacon message. However, the use of fixed pseudo-identity is not suitable for protecting the privacy of a vehicle, and it must be changed over time to guard against the linking the pseudonym of a vehicle over time. For the protection of vehicle location privacy, various pseudonym-changing strategies have been proposed in the literature. Some techniques use the concept of a mix zone [11; 12; 13; 14; 15] to hide the vehicle identities in a zone created by the vehicle to change pseudonyms cooperatively. However, the performance of the mix zone is degraded in conditions of lower traffic density [16]. Techniques based on group signatures are introduced [17; 18; 19; 20] to protect location privacy of vehicles in which the broadcast beacons are signed with a key assigned to a group to protect the identity of a vehicle in a group. However, the management of signatures in the group administratively burdensome [16]; large groups have difficulty with managing signatures while small group size impacts privacy protection. Schemes based on a silent period [21; 22; 23] can hide the identity of vehicles. However, these schemes have a detrimental effect for road safety applications. To overcome the onward limitations of existing schemes, we propose a novel scheme, the Crowd-based Mix Context (CMC) method that efficiently provides location privacy protection under diverse vehicle traffic conditions. The existing pseudonym changing scheme, Ref. [24] addresses the problem of location privacy in mix zones under lower traffic density. It uses a concept of creating fake pseudonyms to anonymize the vehicle in the concerned region. However, generating fake pseudonyms in large quantities impact VANET applications and create computational overheads for the vehicle OBU. If a single-vehicle creates fake pseudonyms for anonymity purposes, the attacker may be able to find similarities in beacon messages, to ascertain that only one vehicle is on the road. Furthermore, fake pseudonyms create a liability issue in the network. The work undertaken in [25] is based on both mix zones and silent periods, where a large number of vehicles gather and anonymize identities in silent mode. However, while this works well in an urban scenario that consists of a higher number of vehicles, it is not consistent in the case of lower congested areas such as highways in which vehicles may rarely change pseudonyms [26]. Therefore, to preserve the location privacy of a vehicle, there is a need for an efficient approach that works under various traffic density conditions and also provides privacy outside mix zone areas. In this paper, we propose a distributed scheme CMC that offers privacy protection to vehicles in VANETs. In this paper, the terms network, road network, vehicular network, vehicular communication network and VANETs denote interchangeably and they all refer to vehicular ad-hoc networks. Our contributions in this paper are given below. 1.