A New Mobile Online Social Network based Location Sharing with Enhanced Privacy Protection

Location based services (LBSs), which are useful applications of mobile online social network (mOSN), exploit various geographic properties. Location sharing helps people to share their current locations with designated friends and is one important primitive to construct the LBSs. The recent reports showed that a poorly designed location sharing scheme could easily allow the privacy of users to be violated. Over years, lots of efforts are made to provide a privacy-preserving location sharing, but none of them is satisfactory. To address this issue, we introduce a new location sharing scheme in mOSNs with a strong user privacy protection mechanism such that (a) the user's current location as well as (b) the list of friends who will learn the user's current location will be protected from any unintended entity, while the designated friends in the list will learn the exact location of the user. For this purpose, we introduce a new cryptography primitive called the functional pseudonym scheme based on Lagrange polynomial with the public social network IDs of the designated friends. Then, the pseudonym of a user is posted on the server along with the current location of the user. While each user can see every posted messages (pseudonym and location pairs), the actual identify of the originator of each pair can be verified only by designated friends, whose identities are used to compute the pseudonym. Most importantly, unlike any of the existing counterparts, our scheme does not assume neither a trusted server nor pre-established secret among the friends.