@misc{cryptoeprint:2012:318,
author = {Daniel J. Bernstein and Tanja Lange},
title = {Non-uniform cracks in the concrete: the power of free precomputation},
howpublished = {Cryptology ePrint Archive, Report 2012/318},
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.