@misc{cryptoeprint:2015:399,
author = {Abderrahmane Nitaj and Tajjeeddine Rachidi},
title = {New attacks on RSA with Moduli $N=p^rq$},
howpublished = {Cryptology ePrint Archive, Report 2015/399},
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.