# Positioning Information Privacy in Intelligent Transportation Systems:
## 3 Vehicle Location Protocols Using Additional Information  
Previously listed methods allow for the design of an effective hybrid system meeting the necessary security requirements and being both accurate and fast in determining the location [83]. A number of experiments have already been carried out, proving the benefits of such utilization [84; 85]. The grouping could be done as following. As for the first strategy, we assume having 'beacon' and 'common' nodes in the system. The modification is such that the beacon node is a node where a passenger with a smartphone is present. Furthermore, the smartphone can identify the location more accurately due to cellular signal presence. Common nodes are the nodes where the smartphone does not transmit any information about the location. In this case, the beacon nodes are polled to receive it. At the same time, all vehicles monitor their surroundings for infrastructure units and corresponding RSSI values. The protocol execution example is shown in Figure 2 for a beacon node and a common node. A beacon vehicle has a GNSS receiver and a list of available infrastructure access points (APs). At this moment, a common node is location-unaware. Hence it requests the beacon node for a list of available infrastructure APs. In the reply, the beacon node also transmits an approximate location in addition to requested data. Indeed, the positioning techniques as we know them today are relying on their own collected location data. The systems of tomorrow would also rely on neighbors and infrastructure thus moving the information security aspects to an entirely new level. In this section, we consider possible protocols for data exchange between a vehicle not possessing reliable location information and its surrounding roadside elements and other traffic participants carrying location data. The crucial feature of these protocols is the presence or absence of anonymity of the vehicle requesting location information. The anonymity of the request for location is an essential property of the protocol, and its availability requires significant complication of the protocol. The anonymity in this work is considered as the process of 'hiding' the actual vehicle location. Generally, the localization process could be viewed as follows. * First, the 'indirect' distance to the static trusted nodes obtained from the known units (cellular or infrastructure units) is estimated. Mutual authentication also takes place during this phase. * Next, the distances are utilized to estimate the location of the node through classical geometry by, for example, triangulation. We further list the potential options for securely executing the first phase. Distance Determination without Anonymity  
In 2004, authors proposed a distance-bounding protocol in [86], we further refer to it as protocol P-04. The action here is performed between \(V\)--the vehicle, and \(S\)--the base station. Key constructs utilized by this work are given in Table 1. The protocol is shown in Figure 3. \begin{table}
\begin{tabular}{l l} \hline \hline
**Construct** & **Description** \\ \hline \(V\) & Target vehicle \\ \(S\) & Target base station \\ \(N_{V},N_{V}^{\prime},N_{S}\) & Random nonces \\ \(h(x)\) & Hashing function \\ \(id_{x}\) & Unique identification number \\ \(K_{VS}\) & Pairwise symmetric key \\ \(sig_{K_{VS}}(x)\) & Signature by \(K_{VS}\) \\ \(d_{VS}\) & Distance between nodes \\ \(t_{VS}\) & Time between message exchange \\ \(\sigma\) & Delay in response to the base station \\ \(\overline{t_{VS}}\) & Miscalculated time of passing the signal \\ \(F(x)\) & Homomorphic transformation \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Key constructs utilized in this work. Figure 2: An illustration of communication between common and beacon nodes. First, a shared symmetric key must be generated between the vehicle and the infrastructure node for secure exchange of information. Key generation algorithm depends on the computing power modules installed in the vehicle and base station.