Please consider referencing the following conference paper in addition to the journal paper.

@InProceedings{nymble-pet07,
  author = {Peter C. Johnson and Apu Kapadia and Patrick P. Tsang and Sean W. Smith},
  title = "{Nymble: Anonymous {IP}-Address Blocking}",
  booktitle = {Proceedings of The Seventh International Symposium on Privacy Enhancing Technologies ({PET}), Ottawa, Canada},
  year = {2007},
  month = jun,
  pages = {113--133},
  series = {LNCS},
  volume = {4776},
  doi = {10.1007/978-3-540-75551-7_8},
  publisher = {Springer-Verlag},
  copyright = {Springer-Verlag}

}


@article{nymble-tdsc,
author = {Patrick P. Tsang and Apu Kapadia and Cory Cornelius and Sean W. Smith},
title = {Nymble: Blocking Misbehaving Users in Anonymizing Networks},
journal ={IEEE Transactions on Dependable and Secure Computing},
volume = {8},
number = {2},
year = {2011},
month = {March--April},
pages = {256--269},
doi = {10.1109/TDSC.2009.38},
}