@misc{cryptoeprint:2010:631,
author = {Michal Rjaško},
title = {Black-box property of Cryptographic Hash Functions},
howpublished = {Cryptology ePrint Archive, Report 2010/631},
year = {2010},
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.