@misc{cryptoeprint:2004:224,
author = {Marc Joye and David Naccache and Stephanie Porte},
title = {The Polynomial Composition Problem in (Z/nZ)[X]},
howpublished = {Cryptology ePrint Archive, Report 2004/224},
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.