@misc{cryptoeprint:2007:158,
author = {Mridul Nandi},
title = {A Simple Security Analysis of Hash-CBC and a New Efficient One-Key Online Cipher},
howpublished = {Cryptology ePrint Archive, Report 2007/158},
year = {2007},
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.