@misc{cryptoeprint:2004:258,
author = {S.S. Al-Riyami and J. Malone-Lee and N.P. Smart},
title = {Escrow-Free Encryption Supporting Cryptographic Workflow},
howpublished = {Cryptology ePrint Archive, Report 2004/258},
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.