GOTCHA password hackers!

@article{Blocki2013GOTCHAPH,
  title={GOTCHA password hackers!},
  author={Jeremiah Blocki and Manuel Blum and Anupam Datta},
  journal={Proceedings of the 2013 ACM workshop on Artificial intelligence and security},
  year={2013}
}
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… 

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