@misc{cryptoeprint:2005:447,
author = {Vladimir Shpilrain and Alexander Ushakov},
title = {A new key exchange protocol based on the decomposition problem},
howpublished = {Cryptology ePrint Archive, Report 2005/447},
year = {2005},
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.