@misc{cryptoeprint:2004:364,
author = {Krystian Matusiewicz and Josef Pieprzyk},
title = {Finding good differential patterns for attacks on SHA-1},
howpublished = {Cryptology ePrint Archive, Report 2004/364},
year = {2004},
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.