# A Privacy-Preserving Protocol for Utility-Based Routing in DTNs
## 2 Related Work  
At present, the existing privacy-preserving routing protocols in DTNs are mainly classified into the following four categories: ID privacy [8; 9; 10], location privacy [11; 12; 13], message content privacy [14; 15; 16; 17; 18], and routing utility privacy [19; 20; 21]. [PERSON] et al. [8] proposed the first anonymous communication solution for DTNs and introduced a new anonymous authentication protocol as a part of it. Furthermore, they presented a security infrastructure for DTNs to provide efficient secure communication based on ID-based cryptography. [PERSON] et al. [9] proposed a social-based privacy-preserving packet forwarding protocol, called SPRING, for vehicular delay-tolerant networks. SPRING can achieve conditional privacy preservation and resist most attacks existing in vehicular delay-tolerant networks. [PERSON] et al. [12] proposed the antilocalization anonymous routing (ALAR) protocol for DTNs. ALAR can protect the sender's location privacy through message fragmentation and forwarding each segment to different receivers. [PERSON] et al. [13] propose a novel fully distributed and collaborative k-anonymity protocol, called LPAF, to protect users' location information and ensure better privacy while forwarding messages. [PERSON] et al. [14] presented ARDEN, an anonymous communication mechanism for DTNs based on a modified onion routing architecture. ARDEN uses attribute-based encryption (ABE) to specify and manage groups that may decrypt and forward messages and enhances the anonymity of the underlying communications. [PERSON] et al. [15] proposed PSaD: a privacy-preserving social-assisted content dissemination protocol in DTNs. PSaD applies users' verifiable attributes to establish their social relationships in terms of identical attributes in a privacy-preserving way. Besides, to provide the confidentiality of contents, PSaD enables users to encrypt contents before the dissemination process and only allows users who have particular attributes to decrypt them. [PERSON] et al. [16] proposed a data sanitization method collectively manipulating user profile and friendship relations and employing collective methods to protect against inference attacks in social networks. [PERSON] et al. [17] proposedan advanced framework for opportunistic routing protocols, providing the following properties: confidentiality of the nodes' routing metric, anonymous authentication, and efficient key agreement for pairwise communication. [PERSON] et al. [18] proposed a novel message-forwarding algorithm that utilizes random walks to deliver messages to their destinations. By removing the requirement to list all the intermediate nodes on the end-to-end path, the method enhances the anonymity of the underlying communications. [PERSON] et al. [19] proposed a privacy-preserving probabilistic prediction-based routing (4 PR) protocol that forwards messages by comparing aggregated information about communities instead of individual nodes. [PERSON] et al. [20] proposed a distributed strategy to protect the aforementioned private information in utility-based DTN routing algorithms while still guaranteeing the correctness of packet forwarding. [PERSON] et al. [21] proposed an enhanced privacy-preserving opportunistic routing protocol (ePRIVO) for vehicular delay-tolerant networks. ePRIVO addresses the problem of vehicles taking routing decisions while keeping their information private; i.e., vehicles calculate their similarity and/or compare their routing metrics in a private manner using the Paillier homomorphic encryption scheme. The above privacy-preserving protocols have been proposed to protect the nodes' privacy information, but cannot collect encounter information to deduce the real utility of utility-based routing. [PERSON] et al. [10] proposed a protocol named FaceChange that can support both anonymizing real IDs among neighbor nodes and collecting encounter information. For node anonymity, two encountering nodes communicate anonymously.