@misc{cryptoeprint:2015:802,
author = {Shahram Khazaei and Siavash Ahmadi},
title = {Ciphertext-only attack on d*d Hill in O(d13^d)},
howpublished = {Cryptology ePrint Archive, Report 2015/802},
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.