@misc{cryptoeprint:2014:238,
author = {Jo\"el Alwen and Vladimir Serbinenko},
title = {High Parallel Complexity Graphs and Memory-Hard Functions},
howpublished = {Cryptology ePrint Archive, Report 2014/238},
year = {2014},
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.