@misc{cryptoeprint:2010:552,
author = {Carmit Hazay and Yehuda Lindell},
title = {A Note on Zero-Knowledge Proofs of Knowledge and the ZKPOK Ideal Functionality},
howpublished = {Cryptology ePrint Archive, Report 2010/552},
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.