@misc{cryptoeprint:2007:187,
author = {Andrew Moss and Dan Page and Nigel Smart},
title = {Executing Modular Exponentiation on a Graphics Accelerator},
howpublished = {Cryptology ePrint Archive, Report 2007/187},
year = {2007},
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.