@misc{cryptoeprint:2011:542,
author = {Yang Lu and Jiguo Li},
title = {Certificate-Based Signcryption: Security Model and Efficient Construction},
howpublished = {Cryptology ePrint Archive, Report 2011/542},
year = {2011},
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.