  Widespread deployment of RFID system arises security and privacy concerns of
users. There are several proposals are in the literature to avoid these
concerns, but most of them provides reasonable privacy at the cost of search
complexity on the server side. The search complexity increases linearly with
the number of tags in the system. Some schemes use a group based approach to
solve the search complexity problem. In this paper, we proposed a group based
authentication protocol for RFID system which is based on some characteristics
of cyclic groups. The scheme uses only bitwise XOR and mod operation for the
computational work. Also, the scheme does not use any pseudo-number generator
on the tag-side. We use two benchmark metric based on anonymity set to measure
the privacy level of the system when some tags are compromised by an adversary.
We present some simulation results which show that the scheme preserves high
level of privacy and discloses very less amount of information when some tags
are compromised. Furthermore, it's formal and informal analysis shows that our
scheme preserves information privacy as well as un-traceability and also
withstand against various well known attacks.
