Hello, Are You Human?
Jun Xu, Irfan A. Essa, Richard J. Lipton · SMARTech Repository (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 "who are you?"), and upon the correct answer to this question, can prove a principal to be a human being instead of a computer program. We demonstrate that the humanizer helps solve problems in network security and E-commerce that existing security measures can not address properly. A key component of this "are you human?" authentication process is a new type of trapdoor one-way hash function, called Turing-resistant hashing. It transforms a character string (the preimage) into a graphical form (the image) in such a way that a human being won't have any problem recovering the preimage through the trapdoor of human pattern recognition skills, while a computer program, essentially a Turing machine, will not be able to decode it or make a correct guess of the preimage with non-negligible probability. Based on this hash function, we design a stateless generic humanizer that can be parameterized for use in various real-world applications.