@misc{cryptoeprint:2012:476,
author = {Shay Gueron},
title = {A j-lanes tree hashing mode and j-lanes SHA-256},
howpublished = {Cryptology ePrint Archive, Report 2012/476},
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.