@misc{cryptoeprint:2010:305,
author = {Marten van Dijk and Ari Juels},
title = {On the Impossibility of Cryptography Alone for Privacy-Preserving Cloud Computing},
howpublished = {Cryptology ePrint Archive, Report 2010/305},
year = {2010},
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.