Yasuo Hatano Kunihiko Miyazaki Toshinobu Kaneko Cryptographic Approch for Workflow Systems. 75-86 2008 II3E http://dx.doi.org/10.1007/978-0-387-85691-9_7 conf/i3e/2008 db/conf/i3e/i3e2008.html#HatanoMK08