@misc{cryptoeprint:2012:649,
author = {Yannick Seurin and Joana Treger},
title = {A Robust and Plaintext-Aware Variant of Signed ElGamal Encryption},
howpublished = {Cryptology ePrint Archive, Report 2012/649},
year = {2012},
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.