Cryptology ePrint Archive: BibTeX Citation of Report 2007/003

@misc{cryptoeprint:2007:003,
    author = {Johann Groszschaedl and Alexander Szekely and Stefan Tillich},
    title = {The Energy Cost of Cryptographic Key Establishment in Wireless Sensor Networks},
    howpublished = {Cryptology ePrint Archive, Report 2007/003},
    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.