@misc{cryptoeprint:2012:275,
author = {Samuel Neves and Jean-Philippe Aumasson},
title = {Implementing BLAKE with AVX, AVX2, and XOP},
howpublished = {Cryptology ePrint Archive, Report 2012/275},
year = {2012},
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.