@misc{cryptoeprint:2013:575,
author = {Nilanjan Datta and Mridul Nandi},
title = {Equivalence between MAC and PRF for Blockcipher based Constructions},
howpublished = {Cryptology ePrint Archive, Report 2013/575},
year = {2013},
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.