@misc{cryptoeprint:2010:071,
author = {Didier Alqui\'e},
title = {2-round Substitution-Permutation and 3-round Feistel Networks have bad Algebraic Degree},
howpublished = {Cryptology ePrint Archive, Report 2010/071},
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.