@inproceedings{backes05cryptographically,
  author       = {Backes, Michael and Camenisch, Jan and Sommer, Dieter},
  title        = {Cryptographically Secure Anonymous Access Control with Accountability},
  booktitle    = {Proceedings of 4th ACM Workshop on Privacy in the Electronic  Society (WPES)},
  month        = {November},
  year         = {2005},
  pages        = {40-46}
}