@misc{cryptoeprint:2003:092,
author = {Muxiang Zhang},
title = {Provably-Secure Enhancement on 3GPP Authentication and Key Agreement Protocol},
howpublished = {Cryptology ePrint Archive, Report 2003/092},
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.