@misc{cryptoeprint:2006:098,
author = {Makoto Sugita, Mitsuru Kawazoe, Hideki Imai},
title = {Gr\"obner Basis Based Cryptanalysis of SHA-1},
howpublished = {Cryptology ePrint Archive, Report 2006/098},
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.