@misc{cryptoeprint:2005:264,
author = {Boaz Tsaban},
title = {On an authentication scheme based on the Root Problem in the braid group},
howpublished = {Cryptology ePrint Archive, Report 2005/264},
year = {2005},
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.