@misc{cryptoeprint:2006:055,
author = {M. Nandi and D. R. Stinson},
title = {Multicollision Attacks on some Generalized Sequential Hash Functions },
howpublished = {Cryptology ePrint Archive, Report 2006/055},
year = {2006},
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.