@misc{cryptoeprint:2004:025,
author = {Hamilton E. Link and William D. Neumann},
title = {Clarifying Obfuscation: Improving the Security of White-Box Encoding},
howpublished = {Cryptology ePrint Archive, Report 2004/025},
year = {2004},
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.