@misc{cryptoeprint:2007:125,
author = {Jean Paul Degabriele and Kenneth G. Paterson},
title = {Attacking the IPsec Standards in Encryption-only Configurations},
howpublished = {Cryptology ePrint Archive, Report 2007/125},
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.