@misc{cryptoeprint:2012:162,
author = {Jayaprakash Kar},
title = {Provably Secure Online/Off-line Identity-Based Signature Scheme forWireless Sensor Network},
howpublished = {Cryptology ePrint Archive, Report 2012/162},
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.