@misc{cryptoeprint:2004:112,
author = {M. Sugita and M. Kawazoe and H. Imai},
title = {Relation between XL algorithm and Groebner Bases Algorithms},
howpublished = {Cryptology ePrint Archive, Report 2004/112},
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.