@misc{cryptoeprint:1996:011,
author = {Moni Naor and Omer Reingold},
title = {On the Construction of Pseudo-Random Permutations: Luby-Rackoff Revisited},
howpublished = {Cryptology ePrint Archive, Report 1996/011},
year = {1996},
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.