@misc{cryptoeprint:2011:044,
author = {G. N. Purohit , Asmita Singh Rawat},
title = {Fast Scalar Multiplication in ECC using The Multi base Number System.},
howpublished = {Cryptology ePrint Archive, Report 2011/044},
year = {2011},
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.