@misc{cryptoeprint:2009:347,
author = {Douglas Wikstr{\"o}m},
title = {An Efficient Concurrent Repetition Theorem},
howpublished = {Cryptology ePrint Archive, Report 2009/347},
year = {2009},
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.