@misc{cryptoeprint:2011:220,
author = {István Vajda},
title = {Framework for Security Proofs for On-demand Routing Protocols in Multi-Hop Wireless Networks},
howpublished = {Cryptology ePrint Archive, Report 2011/220},
year = {2011},
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.