# Adaptive Authentication Protocol Based on Zero-Knowledge Proof
## 2 Analysis of Authentication Protocols Used to Ensure Confidentiality in VANET  
Since the computing power of the _OBU_ is relatively small to ensure a high level of confidentiality in the authentication protocol, with minimal time spent on its execution, the use of Vehicular Cloud Computing (VCC) is proposed in a number of works [18; 19; 20; 21; 22]. The main advantage of this approach is the reduction in the time required for the authentication of _OBU_ and _RSU_. In addition, VCC provides a number of services, such as data storage, vehicle maintenance, road condition and their loading in real-time, as well as vehicle traffic management, road accidents data, etc. However, the use of multi-factor authentication proposed in [18] has a disadvantage, which is associated with an increase in the time spent on user identification, since this procedure uses several types of data. In references [19; 20; 21], the use of symmetric and asymmetric ciphers to increase the level of confidentiality is proposed. In [22] an authentication protocol is proposed that uses identifiers. However, this does not ensure the anonymity of the protocol participants. In references [23; 24; 25], electronic digital signatures are used for authentication. However, the disadvantage of this authentication method is the need to deliver public and secret keys to each \(RSU\) and \(OBU\). In references [26], an approach was proposed in which vehicles located near one \(RSU\) form a single group. In this case, the \(OBU\)s data keys will be known to this \(RSU\). The disadvantage of this solution is that if the \(RSU\) is compromised, \(OBU\)s keys will become available to an attacker. In references [27; 28; 29], the authors justified the expediency of using encryption systems with secret keys in the authentication protocol. The purpose of these works is to increase the speed of the prover's authentication. The disadvantages of such authentication protocols include the possibility of intercepting secret keys when they are delivered to \(RSU\)s and \(OBU\)s.  
In reference [30], the message authentication code (MAC) is proposed for vehicle authentication. The prover generates a message authentication code (MAC) using a shared, secret key. The verifier verifies the prover using MAC and then receives the transmitted message. The advantage of this method is the minimal time spent on authentication. However, this method has low resistance to a number of attacks aiming to replace MAC. As a result, the intruder will be able to intercept all incoming and outgoing traffic passing through the user's system and obtain the confidential data contained therein. In references [31; 32], ring signatures are proposed for authentication. In this case, the signatory must obtain the public keys of all other participants in order to generate a signature. Then, he uses all the public keys and his private key. As a result, the verifier does not know exactly who signed the message, but is aware that the signatory is included in the list of legal users. The disadvantage of this authentication method is the need for each legal owner to receive the keys of all vehicle owners. The principles of building an authentication system that uses an optimized signature generation and verification scheme based on lattice-based cryptography are considered in [33]. This approach allows for signatures to be generated based on asymmetric encryption using lattice theory problems. The advantage of this approach is an 18% reduction in the length of the blind signature and 30% reduction in the signature generation time. However, the disadvantage of this authentication system is the lack of an accurate method to assess the complexity of lattice algorithms in relation to existing types of attack. Therefore, this authentication method has no formal proof of security. The results of the analysis allow us to draw the following conclusions: 1.