@misc{cryptoeprint:2015:310,
author = {Igor Semaev},
title = {New algorithm for the discrete logarithm problem on elliptic curves},
howpublished = {Cryptology ePrint Archive, Report 2015/310},
year = {2015},
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.