  Location-Based Services (LBSs) provide valuable services, with convenient
features for mobile users. However, the location and other information
disclosed through each query to the LBS erodes user privacy. This is a concern
especially because LBS providers can be honest-but-curious, collecting queries
and tracking users' whereabouts and infer sensitive user data. This motivated
both centralized and decentralized location privacy protection schemes for
LBSs: anonymizing and obfuscating LBS queries to not disclose exact
information, while still getting useful responses. Decentralized schemes
overcome disadvantages of centralized schemes, eliminating anonymizers, and
enhancing users' control over sensitive information. However, an insecure
decentralized system could create serious risks beyond private information
leakage. More so, attacking an improperly designed decentralized LBS privacy
protection scheme could be an effective and low-cost step to breach user
privacy. We address exactly this problem, by proposing security enhancements
for mobile data sharing systems. We protect user privacy while preserving
accountability of user activities, leveraging pseudonymous authentication with
mainstream cryptography. We show our scheme can be deployed with off-the-shelf
devices based on an experimental evaluation of an implementation in a static
automotive testbed.
