We obtain minimax lower bounds on the regret for the classical two-armed bandit problem. We provide a nite-sample minimax version of the well-known log n asymptotic lower bound of Lai and Robbins. Also, in contrast to the logn asymptotic results on the regret, we show that the minimax regret is achieved by mere random guessing under fairly mild conditions on the set of allowable con gurations o...

We investigate the problem of guessing a random vector X within distortion level D. Our aim is to characterize the best attainable performance in the sense of minimizing, in some probabilistic sense, the number of required guesses G(X) until the error falls below D. The underlying motivation is that G(X) is the number of candidate codewords to be examined by a rate-distortion block encoder unti...

This paper introduces Freestyle, a randomized and variable round version of the ChaCha cipher. Freestyle uses the concept of hash based halting condition where a decryption attempt with an incorrect key is likely to take longer time to halt. This makes Freestyle resistant to key-guessing attacks i.e. brute-force and dictionary based attacks. Freestyle demonstrates a novel approach for ciphertex...

Mobile devices, such as smartphones and tablets, frequently store confidential data, yet implementing a secure device unlock functionality is non-trivial due to restricted input methods. Graphical knowledge-based schemes have been widely used on smartphones and are generally well adapted to the touchscreen interface on small screens. Recently, graphical password schemes based on emoji have been...

Recognition-based graphical passwords are a suggested alternative authentication mechanism which have received substantial attention in research literature. The literature often presents new schemes, usability studies or propose countermeasures for specific attacks. Whilst this is beneficial, it does not allow for consistent comparison of the security of recognition-based graphical password sch...

Let (X, Y) be a pair of discrete random variables with X taking one of M possible values. Suppose the value of X is to be determined, given the value of Y, by asking quest ions of the form “Is X equal to z?” until the answer is “Yes.” Let G(r 1 y) denote the number of guesses in any such guessing scheme when X = x, Y = y. W e prove that 1 1+/J E[G(X IY)‘] 2 (l+InM)-P~ for any p > 0. This provid...

We compared the effects of guessing vs. choosing an upcoming task. In a task-switching paradigm with four tasks, two groups of participants were asked to either guess or choose which task will be presented next under otherwise identical conditions. The upcoming task corresponded to participants' guesses or choices in 75 % of the trials. However, only participants in the Choosing condition were ...

Numerous recent papers focus on standard recurrent nets' problems with tasks involving long-term dependencies. We solve such tasks by random weight guessing (RG). Although RG cannot be viewed as a reasonable learning algorithm we nd that it often outperforms previous, more complex methods on widely used benchmark problems. One reason for RG's success is that the solutions to many of these bench...