@misc{cryptoeprint:2004:238,
author = {Amit K Awasthi and Sunder Lal},
title = {Security Analysis of A Dynamic ID-based Remote User Authentication Scheme},
howpublished = {Cryptology ePrint Archive, Report 2004/238},
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.