  For many years, the pay-TV system has attracted a lot of users. Users have
recently expressed the desire to use mobile TV or mobile payment via anonymous
protocols. The mobile users have also received their services over cellular
communications networks. Each mobile device receives services from each head
end systems. With increasing numbers of users and the expansion of Internet,
user's privacy has become crucial important. When a device leaves the head end
system's range, it must receive services from another head end system. In this
paper, we review Chen et al's scheme and we highlight some weaknesses,
including privilege insider attack and user traceability attack. Finally, we
alleviate the scheme and analyze the alleviated scheme using both heuristic and
formal methods.
