@misc{cryptoeprint:2005:460,
author = {Tomas Rosa},
title = {One-Time HNP or Attacks on a Flawed El Gamal Revisited},
howpublished = {Cryptology ePrint Archive, Report 2005/460},
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.