@misc{cryptoeprint:2011:574,
author = {Jia Xu and Ee-Chien Chang and Jianying Zhou},
title = {Towards Efficient Provable Data Possession in Cloud Storage},
howpublished = {Cryptology ePrint Archive, Report 2011/574},
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.