Provide Privacy for Mobile P2P Systems Jinsong Han 1 , Yanmin Zhu 1 , Yunhao Liu 1 , Jianfeng Cai 2 , Lei Hu 3 1 Department of Computer Science, Hong Kong University of Science & Technology, Hong Kong 2 Department of Computer Science, Texas A&M University, USA 3 The State Key Laboratory of Information Security, Chinese Academy of Science, Beijing, China {jasonhan, zhuym, liu}@cs.ust.hk, j0c1194@cs.tamu.edu, hu@is.ac.cn Abstract Nowadays privacy and anonymity have become an increasing requirement in wireless networks. However, current mobile peer-to-peer architectures have not taken into account anonymity, especially the mutual anonymity between two nodes. In this paper, we pro- pose a mutual anonymity protocol, called Secret- sharing-based Mutual Anonymity Protocol (SMA), for mobile P2P networks. Our simulation results show that SMA achieves mutual anonymity in mobile P2P net- works with a low cryptography processing overhead. 1. Introduction Wireless technology has promoted mobile peer-to- peer networks into a high flexible information sharing system. In the past years, user privacy requirements have become increasingly urgent, and anonymity issue in such systems has not been fully addressed. In mobile P2P environment, anonymity [1] can be divided into three types: resistant-censorship (or pub- lishing anonymity), initiator or responder anonymity, and mutual anonymity (both initiator and responder anonymity). Strictly defined, mutual anonymity is made up of three parts: an anonymous initiator, an anonymous responder and anonymous communica- tions between the two parties. This paper focuses on decentralized mobile P2P networks[5, 7, 11]. All participants in a mobile P2P system communicate with their neighbors. Theoreti- cally no node has any knowledge of other peers two or more hops away. Based on this observation, a mobile P2P network is able to achieve partial anonymity at least among those non-neighboring peers. However, current mobile P2P protocols fail to pro- vide real anonymity guarantees. Since queries are flooded in plain text, contents of these messages are exposed to malicious nodes, and attackers can easily guess the identities of the communication parties. Also, every node is monitored by its neighbors. Hence, mo- bile P2P systems cannot provide initiator and re- sponder anonymity in each node’s very local environ- ment. In this paper, we propose a mutual anonymous pro- tocol, called Secret-sharing-based Mutual Anonymity (SMA). SMA provides initiator and responder ano- nymity, as well as communication security in mobile P2P systems. In SMA, we employ a secret sharing scheme to anonymously issue queries, and use the in- formation dispersal algorithm (IDA) [12] together with the onion routing [20] to redundantly deliver requested data. The rest of this paper is organized as follows. In the next section, we introduce some previous work related to this topic. Section 3 presents the SMA design. In Section 4, we analyze anonymity and security degree of SMA. Simulation results are presented in Section 5. We conclude the work in Section 6. 2. Related Work Initiator anonymity can be achieved by forwarding packets through a predetermined path made by the sender, such as MorphMix [15]and Onion [20]. Instead of allowing initiators to create paths, in Crowds [14] peers randomly selects a succeed peer to build a furtive path. Hordes [19] is similar to Crowd, but deploys multicast services and anonymously sends a reply back to the initiator. Freedom [3] and Tarzan [6] are imple- mented over IP and transport layers and depending on Onion Routing to build main architectures. NICE [23] is based on a Reputation record mechanism or trust interface technology. Peer-to-peer Personal Privacy Protocol (P 5 ) [18], based on a global broadcast channel, aims at mutual anonymity. The basic idea of P 5 is that all participants in the channel send fixed length encrypted meaningful or noise messages at a fixed rate as if all participants are grouped in a logic ring. Each joining peer is This work was partially supported by Hong Kong RGC DAG 04/ 05.EG01, NSFC 60373041. This is the Pre-Published Version