Acoustic Covert Channels for Mobile Phone Platforms

Master Thesis



[Abstract of final thesis] Mobile smart phones store sensitive data. Mechanisms to prevent leakage from mobile phones are vigorously developed. This leads to attackers developing an interest in unconventional methods for data exfiltration. Covert channels can be used to bypass these mechanisms. An experiment using acoustic covert channels on mobile phones is constructed to evaluate the feasibility and the limits of usable frequencies, transmission speeds, and distances. Furthermore, the possibility of the detection of the covert channel is analyzed. For this, the audio capabilities of different devices are analyzed. Also, detectability through humans and frequency analyzers is evaluated. Furthermore, three different modulations are evaluated: frequency shift keying, phase shift keying and direct sequence spread spectrum. Also, special forms of the modulations are inspected, specifically Gaussian frequency shift keying and the phase shift keying baud 31 used in amateur radio. Two methods to improve error robustness are demonstrated, which are a simple forward error correction with repetition and interleaving, and a modification of the direct sequence spread spectrum called escorting. It is shown that acoustic covert channel can be utilized to successfully exfiltrate data over long distances. Finally, it is shown that the attack can be discovered by the usage of simple tools.

End: 07.05.2015


Student: Markus Brandt

Research Areas: Sichere Mobile Netze



Prof. Dr.-Ing. Matthias Hollick

Technische Universität Darmstadt
Department of Computer Science
Secure Mobile Networking Lab 

Mornewegstr. 32 (S4/14)
64293 Darmstadt, Germany

Phone: +49 6151 16-25472
Fax: +49 6151 16-25471


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