@misc{cryptoeprint:2015:504,
author = {Brice Minaud and Yannick Seurin},
title = {The Iterated Random Permutation Problem with Applications to Cascade Encryption},
howpublished = {Cryptology ePrint Archive, Report 2015/504},
year = {2015},
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.