Cryptology ePrint Archive: BibTeX Citation of Report 2007/100

@misc{cryptoeprint:2007:100,
    author = {Shengbao Wang and Zhenfu Cao},
    title = {Practical Identity-Based Encryption (IBE) in Multiple PKG Environments and Its Applications},
    howpublished = {Cryptology ePrint Archive, Report 2007/100},
    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.