@misc{cryptoeprint:2012:418,
author = {Rafael Martínez-Peláez and Francisco Rico-Novella},
title = {Weaknesses of an Improvement Authentication Scheme using },
howpublished = {Cryptology ePrint Archive, Report 2012/418},
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.