基金Supported by the National High-Tech Research and Development Plan of China under Grant Nos.2006AA01ZA45, 2006AA01Z410 (国家高技术研究发展计划(863)) the National Information Security Research Plan of China under Grant No.2006A30(国家242信息安全计划)+1 种基金 the Electronic Development Fund of the Ministry of Information Industry of China under Grant No.[20061634 (信息产业部电子发展基金) the IBM Ph.D. Fellowship Plan(IBM全球博士生英才计划)