@misc{cryptoeprint:2009:034,
author = {S. Markovski, A. Mileva, V. Dimitrova and D. Gligoroski},
title = {On a Conditional Collision Attack on NaSHA-512},
howpublished = {Cryptology ePrint Archive, Report 2009/034},
year = {2009},
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.