1. College of Information Sciences and Technology, The Pennsylvania State University, PA, USA. E-mails: qzz32@psu.edu, pxl20@psu.edu
2. Security Test, Validation and Measurement Group, National Institute of Standards and Technology, MD, USA. E-mail: anoop.singhal@nist.gov
3. College of Engineering & Computer Science, California State University, Sacramento, CA, USA. E-mail: xiaoyan.sun@csus.edu