@misc{cryptoeprint:2006:381,
author = {Fuw-Yi Yang},
title = {Cryptanalysis on an Algorithm for Efficient Digital Signatures},
howpublished = {Cryptology ePrint Archive, Report 2006/381},
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.