# Adaptive Authentication Protocol Based on Zero-Knowledge Proof
## 1 Introduction  
Ensuring confidentiality in modern information systems is a very relevant topic at present. This is due to the expansion of the scope of wireless data-processing and transmission systems, in which an intruder can intercept, read, and modify the transmitted data. Therefore, the use of authentication protocols that effectively resist attacks on information systems has been proposed when projects such as low-orbit satellite communication systems (LOSCS) for the OneWeb global space Internet [1, 2], automatic object identification systems using RFID [3, 4, 5, 6], and the Internet of Things [7, 8, 9] are being developed. A special place among information systems, on which the comfort of modern society largely depends, is occupied by intelligent transportation systems (ITS), particularly the automotive self-organizing network Vehicular Ad Hoc Network (VANET). The use of VANET makes it possible to increase the efficiency and comfort of vehicle movement by providing the vehicle owner with information about the current state of traffic, dangerous sections on the road, and relevant services [10]. This real-time management leads to a reduction in the number of road accidents. As a rule, VANET consists of [11]:* Roadside Units (_RSU_);
* On Board Unit (_OBU_);
* Certificate Authority (CA);
* Service Provider (SP). _OBU_ devices are placed on board the vehicles and used to transmit information about the vehicle's speed of movement and its main parameters. In addition, the owner of the vehicle has access to the Internet and related services with the help of _OBU_. To carry out this data exchange, stationary _RSU_ devices are used, and form a network. The Certificate Authority is a trusted party and designed to generate and deliver secret and public keys for _OBU_s and _RSU_s. The Service Provider provides them with the appropriate services using the appropriate _OBU_'s rights verification mechanism. However, VANET has vulnerabilities, determined by the wireless data transmission channel [12; 13; 14], while providing the comfortable and safe movement of vehicles. Authentication protocols allow us to eliminate some of the vulnerabilities and attacks aiming to obtain confidential information. The analysis of works [15; 16; 17; 18] showed that the authentication protocol should have the following properties:  
* The protocol should have high cryptographic strength without the use of symmetric and asymmetric ciphers, with minimal time spent on its execution;
* The protocol should ensure the confidentiality of the vehicle's route;
* The protocol should have a mechanism that allows the vehicle's owner to change the level of confidentiality depending on the intensity of traffic. _Our Impact_  
1. Based on the properties described above, an authentication protocol has been developed that can adapt its characteristics to the intensity of traffic on the road. Its basis is a zero-knowledge authentication protocol (ZKAP), which will ensure the high confidentiality of the route and anonymity of the vehicle owner. At the same time, this protocol spent minimal time on vehicle identification compared to other ZKAPs, which allows us to increase the volume of traffic and transmit useful information between _OBU_s and _RSU_s. 2. A mechanism has been developed that allows the owner of the vehicle to change the parameters of the authentication protocol. If the traffic intensity on the road is low, then the _OBU_ uses a maximal level of confidentiality. The vehicle's owner reduces the level of confidentiality to a minimal value if the amount of network traffic between _OBU_s and _RSU_s increases in response to greater traffic intensity on the road. Since there is no exchange of useful information during _OBU_ and _RSU_ authentication, a reduction in the level of confidentiality reduces the time needed to determine the status of the vehicle. This will lead to an increase in the amount of transmitted useful information. The structure of the article is as follows.