@misc{cryptoeprint:2014:291,
author = {Antonio Sanso},
title = {Trial multiplication is not optimal but... On the symmetry of finite cyclic groups (Z/pZ)∗},
howpublished = {Cryptology ePrint Archive, Report 2014/291},
year = {2014},
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.