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Open AccessArticle

Password Security as a Game of Entropies

System Security Group, Institute of Applied Informatics, Universität Klagenfurt, 9020 Klagenfurt, Austria
Austrian Institute of Technology, Center for Digital Safety & Security, 1210 Vienna, Austria
Author to whom correspondence should be addressed.
Entropy 2018, 20(5), 312;
Received: 27 February 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 25 April 2018
(This article belongs to the Special Issue Information Theory in Game Theory)
We consider a formal model of password security, in which two actors engage in a competition of optimal password choice against potential attacks. The proposed model is a multi-objective two-person game. Player 1 seeks an optimal password choice policy, optimizing matters of memorability of the password (measured by Shannon entropy), opposed to the difficulty for player 2 of guessing it (measured by min-entropy), and the cognitive efforts of player 1 tied to changing the password (measured by relative entropy, i.e., Kullback–Leibler divergence). The model and contribution are thus twofold: (i) it applies multi-objective game theory to the password security problem; and (ii) it introduces different concepts of entropy to measure the quality of a password choice process under different angles (and not a given password itself, since this cannot be quality-assessed in terms of entropy). We illustrate our approach with an example from everyday life, namely we analyze the password choices of employees. View Full-Text
Keywords: game theory; security; entropy; passwords game theory; security; entropy; passwords
MDPI and ACS Style

Rass, S.; König, S. Password Security as a Game of Entropies. Entropy 2018, 20, 312.

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