@misc{cryptoeprint:2008:073,
author = {Hovav Shacham and Brent Waters},
title = {Compact Proofs of Retrievability},
howpublished = {Cryptology ePrint Archive, Report 2008/073},
year = {2008},
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.