@misc{cryptoeprint:2015:219,
author = {Prakruti C, Sashank Dara and V.N. Muralidhara},
title = {Efficient Format Preserving Encrypted Databases},
howpublished = {Cryptology ePrint Archive, Report 2015/219},
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.