1. Information Security Laboratory, KDDI Research, Inc., 2-1-15 Ohara, Fujimino-shi, Saitama 356-8502 and Japan, --- Select a Country ---
2. Department of Computer Science and Engineering, University of North Texas, Denton, TX 76207 and U.S.A., --- Select a Country ---
3. Department of Mathematical Informatics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 and Japan, --- Select a Country ---