Many security primitives are based on complete mathematical problems. Using hard/complete AI problems for security is emerging as an exciting new paradigm, but has been under-explored. In this paper, it present a new security primitive based on hard AI problems, namely, a novel family of graphical password systems built on top of Captcha technology, which they call Captcha as graphical passwords (CaRP). CaRP is both a Captcha and a graphical password scheme. CaRP addresses a number of security

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... roblems altogether, such as online guessing attacks, relay attacks, and, if combined with dual-view technologies, shoulder-surfing attacks. Notably, a CaRP password can be found only probabilistically by automatic online guessing attacks even if the password is in the search set. CaRP also offers a novel approach to address the well-known image hotspot problem in popular graphical password systems, such as Pass Points, that often leads to weak password choices. CaRP is not a panacea, but it offers reasonable security and usability and appears to fit well with some practical applications for improving online security.