@misc{cryptoeprint:2010:072,
author = {Didier Alqui\'e},
title = {Approximating Addition by XOR: how to go all the way},
howpublished = {Cryptology ePrint Archive, Report 2010/072},
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.