@misc{cryptoeprint:2006:244,
author = {Dima Ruinskiy, Adi Shamir, Boaz Tsaban},
title = {Length-based cryptanalysis: The case of Thompson's Group},
howpublished = {Cryptology ePrint Archive, Report 2006/244},
year = {2006},
note = {\url{http://eprint.iacr.org/}},
}
You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.