@misc{cryptoeprint:2013:248,
author = {Neal Koblitz and Alfred Menezes},
title = {Another Look at Security Theorems for 1-Key Nested MACs},
howpublished = {Cryptology ePrint Archive, Report 2013/248},
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.