Shinji Yamane Jiahong Wang Hironobu Suzuki Norihisa Segawa Yuko Murayama Rethinking OpenPGP PKI and OpenPGP Public Keyserver http://arxiv.org/abs/cs.CY/0308015 2003 CoRR cs.CY/0308015 db/journals/corr/corr0308.html#cs-CY-0308015 informal publication