@misc{cryptoeprint:2003:239,
author = {Ran Canetti},
title = {Universally Composable Signatures, Certification and Authentication},
howpublished = {Cryptology ePrint Archive, Report 2003/239},
year = {2003},
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.