@misc{cryptoeprint:2011:411,
author = {Debiao He},
title = {Comments on a password authentication and update scheme based on elliptic curve cryptography},
howpublished = {Cryptology ePrint Archive, Report 2011/411},
year = {2011},
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.