@misc{cryptoeprint:2003:126,
author = {Sattam S. Al-Riyami and Kenneth G. Paterson},
title = {Certificateless Public Key Cryptography},
howpublished = {Cryptology ePrint Archive, Report 2003/126},
year = {2003},
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.