Niklas Büscher

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CAPTCHAs are small puzzles which should be easily solv-able by human beings but hard to solve for computers. They build a security cornerstone of the modern Internet service landscape, deployed in essentially any kind of login service, allowing to distinguish authorized human beings from automated attacks. One of the most popular and successful systems(More)
Practical hardness results are necessary to select parameters for cryptographic schemes. Cryptographic challenges proved to be useful for determining the practical hardness of computational problems that are used to build public-key cryptography. However, several of these problems have the drawback that it is not known how to create a challenge for them(More)
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