  Proper privacy protection in RFID systems is important. However, many of the
schemes known are impractical, either because they use hash functions instead
of the more hardware efficient symmetric encryption schemes as a efficient
cryptographic primitive, or because they incur a rather costly key search time
penalty at the reader. Moreover, they do not allow for dynamic, fine-grained
access control to the tag that cater for more complex usage scenarios.
  In this paper we investigate such scenarios, and propose a model and
corresponding privacy friendly protocols for efficient and fine-grained
management of access permissions to tags. In particular we propose an efficient
mutual authentication protocol between a tag and a reader that achieves a
reasonable level of privacy, using only symmetric key cryptography on the tag,
while not requiring a costly key-search algorithm at the reader side. Moreover,
our protocol is able to recover from stolen readers.
