@misc{cryptoeprint:2009:391,
author = {Rikke Bendlin and Ivan Damgård},
title = {Threshold Decryption and Zero-Knowledge Proofs for Lattice-Based Cryptosystems},
howpublished = {Cryptology ePrint Archive, Report 2009/391},
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.