@misc{cryptoeprint:2003:137,
author = {Boaz Tsaban},
title = {Bernoulli numbers and the probability of a birthday surprise},
howpublished = {Cryptology ePrint Archive, Report 2003/137},
year = {2003},
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.