Affiliations: [a] Information Security and Critical Infrastructure Protection Research Laboratory, Department of Informatics, Athens University of Economics & Business, Athens, Greece. E-mails: [email protected], [email protected] | [b] Department of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi, Greece. E-mails: [email protected], [email protected] | [c] Joint Research Center, European Commission, Ispra Varese, Italy. E-mail: [email protected]
Correspondence:
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Corresponding author: Dimitris Gritzalis, Information Security and Critical Infrastructure Protection Research Laboratory, Department of Informatics, Athens University of Economics & Business (AUEB), 76 Patission Ave., Athens, GR-10434, Greece. Tel.: +30 210 8203505; E-mail: [email protected].
Abstract: Spam over Internet Telephony (SPIT) is a potential source of disruption in Voice over IP (VoIP) systems. The use of anti-SPIT mechanisms, such as filters and audio CAPTCHA (Completely Automated Public Turing Test to Tell Computer and Humans Apart) can prevent unsolicited calls and lead to less unwanted traffic. In this paper, we present a game-theoretic model, in which the game is played between SPIT senders and internet telephony users. The game includes call filters and audio CAPTCHA, so as to classify incoming calls as legitimate or malicious. We show how the resulting model can be used to decide upon the trade-offs present in this problem and help us predict the SPIT sender’s behavior. We also highlight the advantages in terms of SPIT call reduction of merely introducing CAPTCHA, and provide experimental verification of our results.
Keywords: Spam prevention, Spam over Internet Telephony (SPIT), Game Theory, audio CAPTCHA, Nash equilibria
