@misc{cryptoeprint:2015:973,
author = {Ashwin Jha and Mridul Nandi},
title = {Some Cryptanalytic Results on Zipper Hash and Concatenated Hash},
howpublished = {Cryptology ePrint Archive, Report 2015/973},
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.