You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) 
Chapter Title:  Research Work on Confidentiality 
1. Abstract of Cited Paper (BIB001):  In this paper, to achieve a vehicle user's privacy preservation while improving the key update efficiency of location-based services (LBSs) in vehicular ad hoc networks (VANETs), we propose a dynamic privacy-preserving key management scheme called DIKE. Specifically, in the proposed DIKE scheme, we first introduce a privacy-preserving authentication technique that not only provides the vehicle user's anonymous authentication but enables double-registration detection as well. We then present efficient LBS session key update procedures: 1) We divide the session of an LBS into several time slots so that each time slot holds a different session key; when no vehicle user departs from the service session, each joined user can use a one-way hash function to autonomously update the new session key for achieving forward secrecy. 2) We also integrate a novel dynamic threshold technique in traditional vehicle-to-vehicle (V-2-V) and vehicle-to-infrastructure (V-2-I) communications to achieve the session key's backward secrecy, i.e., when a vehicle user departs from the service session, more than a threshold number of joined users can cooperatively update the new session key. Performance evaluations via extensive simulations demonstrate the efficiency and effectiveness of the proposed DIKE scheme in terms of low key update delay and fast key update ratio.

Literature Review:
In recent years, several methods have been proposed for confidentiality to ensure the safety of data, which contain some useful information from non-registered users in the VANET system. Additionally, it ensured secure communication through a cryptographic solution. In this section, we will explain the existing methods for confidentiality in the VANETs. Sun et al. BIB001 introduced a new security system by protecting the confidentiality of sensitive information using shared key encryptions. The aim of the proposed technique is to ensure that the confidential information of the registered users and tracking of vehicles is completed legitimately, which can be done by integrating the new security requirements and design the sophisticated VANET security system against non-authorized users. However, the confidentiality messages are very crucial where vehicles get the useful data from the Internet and RSUs. Lu et al. BIB002 introduced a dynamic privacy-preserving key management method referred to as DIKE, which is used to achieve and improve the confidentiality of data in location-based services (LBSs) in the VANET system. In order to control the eavesdropping attack, the confidentiality must be well maintained and protect the service contents from these kinds of attacks. In this method, if a user does not engage in the VANET system, then the user may not join the current VANET system, which does not have access to the current LBS content. To gain the confidentiality in an LBS session, all vehicle users that joined are requested to share a secure session key. That session can be used to encrypt service contents.