We introduce GOTCHAs (Generating panOptic Turing Tests to Tell Computers and Humans Apart) as a way of preventing automated offline dictionary attacks against user selected passwords. A GOTCHA is a randomized puzzle generation protocol, which involves interaction between a computer and a human. Informally, a GOTCHA should satisfy two key properties: (1) The puzzles are easy for the human to solve. (2) The puzzles are hard for a computer to solve even if it has the random bits used by the computer to generate the final puzzle --- unlike a CAPTCHA [44]. Our main theorem demonstrates that GOTCHAs can be used to mitigate the threat of offline dictionary attacks against passwords by ensuring that a password cracker must receive constant feedback from a human being while mounting an attack. Finally, we provide a candidate construction of GOTCHAs based on Inkblot images. Our construction relies on the usability assumption that users can recognize the phrases that they originally used to describe each Inkblot image --- a much weaker usability assumption than previous password systems based on Inkblots which required users to recall their phrase exactly. We conduct a user study to evaluate the usability of our GOTCHA construction. We also generate a GOTCHA challenge where we encourage artificial intelligence and security researchers to try to crack several passwords protected with our scheme.
This paper offers a critical appreciation of the theory that the recall of an event entails a generation (or search) process followed by a recognition (or decision) process. The theory provides an elegant account of a variety of experimental findings. On the other hand, the results of a large number of studies run counter to its predictions or are otherwise not readily accommodated by it. It is suggested that the general notion of recall as generation-plus-recognition should be retained as a useful model, but not as a theory to be held strictly accountable to the data. Why Do We Need Memory? Perceiving and Remembering. How Many Kinds of Memory? The Evidence for STM. The Role of Memory in Cognition - Working Memory. Visual Memory and the Visuo-spatial Sketchpad. Attention and the Control of Memory. When Practice Makes Perfect. Organizing and Learning. Acquiring Habits. When Memory Fails. Retrieval. Recollection and Autobiographical Memory. Where Next? Connectionism Rides Again. Knowledge. Memory, Emotion and Cognition. Understanding Amnesia. Treating Memory Problems. Consciousness. Implicit Knowledge and Learning. Implicit Memory and Recollection.