@misc{cryptoeprint:2004:313,
author = {Fuw-Yi Yang, Jinn-Ke Jan, and Woei-Jiunn Jeng},
title = {Cryptanalysis of a threshold proxy signature with known signers},
howpublished = {Cryptology ePrint Archive, Report 2004/313},
year = {2004},
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.