@misc{cryptoeprint:2010:381,
author = {Elena Andreeva and Bart Mennink and Bart Preneel},
title = {Security Reductions of the Second Round SHA-3 Candidates},
howpublished = {Cryptology ePrint Archive, Report 2010/381},
year = {2010},
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.