@misc{cryptoeprint:2009:409,
author = {Abhishek Parakh and Subhash Kak},
title = {A Tree Based Recursive Scheme for Space Efficient Secret Sharing},
howpublished = {Cryptology ePrint Archive, Report 2009/409},
year = {2009},
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.