@misc{cryptoeprint:2010:413,
author = {E.A.Grechnikov},
title = {Collisions for 72-step and 73-step SHA-1: Improvements in the Method of Characteristics},
howpublished = {Cryptology ePrint Archive, Report 2010/413},
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.