• Hello, Are You Human? 

      Xu, Jun; Essa, Irfan A.; Lipton, Richard J. (Georgia Institute of Technology, 2000)
      In this paper, we propose the concept of a humanizer and explore its applications in network security and E-commerce. A humanizer is a novel authentication scheme that asks the question "are you human?" (instead of ...
    • Mandatory Human Participation: A New Scheme for Building Secure Systems 

      Xu, Jun; Essa, Irfan A.; Sung, Min-Ho; Lipton, Richard J. (Georgia Institute of Technology, 2001)
      Mandatory Human Participation (MHP) is a novel authentication scheme that asks the question "are you human?" (instead of "who are you?"), and upon the correct answer to this question, can prove a principal to be a ...