Location-based recommendation services (LBRS) offer great convenience to our daily lives, but ensuring that user privacy remains intact against the honest-but-curious service provider has become a key concern for the LBRS community. Current mainstream approaches to privacy protection in LBRS typically involve introducing a third party or trading off service accuracy. Considering the reality of limited mobile resources of LBRS users, current privacy-centric LBRS solutions tend to incur significant computation and communication costs. To address these shortcomings, we propose an efficient privacy-preserving scheme for LBRS that simultaneously achieves users' query content privacy, identity privacy, and the LBRS provider's data privacy. Specifically, we utilize linkable ring signcryption (LRSC) to achieve the anonymity of users' identities, confidentiality of the query content, and linkability of a user's multiple actions within a valid service period. The integration of an anonymous payment protocol into the LRSC scheme allows users to make anonymous payments and receive encrypted query results from the LBRS provider, guaranteeing privacy and security throughout the entire process. Under the random oracle model (ROM), our scheme is proven to be secure. Furthermore, it significantly outperforms prior works in efficiency, making it suitable for LBRS.

In a modern open network system, data security technologies such as cryptosystems, signature schemes, etc., are indispensable for reliable data transmission. In particular, for a large-scale network, ID-based systems such as the ID-based cryptosystem, the ID-based signature scheme, or the ID-based key distribution system are among the better countermeasures for establishing efficient and secure data transmission systems. The concept of an ID-based cryptosystem has been proposed by Shamir [1], and it is advantageous to public-key cryptosystems because a large public-key file is not required for such a system. This paper proposes an ID-based beta cryptosystem under the security assumptions of the generalized discrete logarithm problem and integer factorization problem, which is one of the earliest realizations in Shamir's sense. Furthermore, we consider the security against a conspiracy of some users in the proposed system, and show the possibility of establishing a more secure system.