  Taking into account of both the huge computing power of intruders and
untrusted cloud servers, we develop an enhanced secure pseudonym scheme to
protect the privacy of mobile cloud data. To face the huge computing power
challenge, we develop an unconditionally secure lightweight network coding
pseudonym scheme. For the privacy issue of untrusted cloud server, we further
design a two tier network coding to decouple the stored mobile cloud data from
the owner pseudonyms. Therefore, our proposed network coding based pseudonym
scheme can simultaneously defend against attackers from both outside and
inside. We implement our proposed two-tier light-weight network coding
mechanism in a group location based service (LBS) using untrusted cloud
database. Compared to computationally secure Hash-based pseudonym, our proposed
scheme is not only unconditionally secure, but also can reduce more than 90
percent of processing time as well as 10 percent of energy consumption.
