@misc{cryptoeprint:2004:093,
author = {Giuseppe Ateniese and Breno de Medeiros},
title = {A Provably Secure Nyberg-Rueppel Signature Variant with Applications},
howpublished = {Cryptology ePrint Archive, Report 2004/093},
year = {2004},
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.