@misc{cryptoeprint:2011:641,
author = {E.A. Grechnikov and A.V. Adinetz},
title = {Collision for 75-step SHA-1: Intensive Parallelization with GPU},
howpublished = {Cryptology ePrint Archive, Report 2011/641},
year = {2011},
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.