  The location-based services provide an interesting combination of cyber and
physical worlds. However, they can also threaten the users' privacy. Existing
privacy preserving protocols require trusted nodes, with serious security and
computational bottlenecks. In this paper, we propose a novel distributed
anonymizing protocol based on peer-to-peer architecture. Each mobile node is
responsible for anonymizing a specific zone. The mobile nodes collaborate in
anonymizing their queries, without the need not get access to any information
about each other. In the proposed protocol, each request will be sent with a
randomly chosen ticket. The encrypted response produced by the server is sent
to a particular mobile node (called broker node) over the network, based on the
hash value of this ticket. The user will query the broker to get the response.
All parts of the messages are encrypted except the fields required for the
anonymizer and the broker. This will secure the packet exchange over the P2P
network. The proposed protocol was implemented and tested successfully, and the
experimental results showed that it could be deployed efficiently to achieve
user privacy in location-based services.
