Covert channels can be used to circumvent system and network policies by establishing communications that have not been considered in the design of the computing system. We construct a covert channel between different computing systems that utilizes audio modulation demodulation to exchange data between the computing systems over the air medium. The underlying network stack is based on a communication system that was originally designed for robust underwater communication. We adapt the communication system to implement covert and stealthy communications by utilizing the ultrasonic frequency range. We further demonstrate how the scenario of covert acoustical communication over the air medium can be extended to multi-hop communications and even to wireless mesh networks. A covert acoustical mesh network can be conceived as a meshed botnet or malnet that is accessible via inaudible audio transmissions. Different applications of covert acoustical mesh networks are presented, including the use for remote keylogging over multiple hops. It is shown that the concept of a covert acoustical mesh network renders many conventional security concepts useless, as acoustical communications are usually not considered. Finally, countermeasures against covert acoustical mesh networks are discussed, including the use of lowpass filtering in computing systems and a host-based intrusion detection system for analyzing audio input and output in order to detect any irregularities.
@cite_29: Near Field Communication (NFC) enables physically proximate devices to communicate over very short ranges in a peer-to-peer manner without incurring complex network configuration overheads. However, adoption of NFC-enabled applications has been stymied by the low levels of penetration of NFC hardware. In this paper, we address the challenge of enabling NFC-like capability on the existing base of mobile phones. To this end, we develop Dhwani, a novel, acoustics-based NFC system that uses the microphone and speakers on mobile phones, thus eliminating the need for any specialized NFC hardware. A key feature of Dhwani is the JamSecure technique, which uses self-jamming coupled with self-interference cancellation at the receiver, to provide an information-theoretically secure communication channel between the devices. Our current implementation of Dhwani achieves data rates of up to 2.4 Kbps, which is sufficient for most existing NFC applications.
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@cite_20: Considers how sound offers features not available with other short-range, low bandwidth communication technologies, such as radio and infrared, enabling communication among small computing devices and humans in a ubiquitous computing environment.
@cite_7: In this article, we'll review various modulation schemes we've worked with previously, covering how to transfer data to nearby smart phones as well as usability and security issues. We'll consider audio networking as a mechanism for introducing data packets into ongoing mobile phone calls. We'll also discuss some real-world problems reported with telephone conferencing and apply audio-networking techniques to them in a case study application.
Using audio as a networking technology has been described by Madhavapeddy, Scott, Tse and Sharp @cite_7 , by Yan, Zhou, Shi and Li @cite_3 and by Lopes and Aguiar @cite_20 . Very recently, Nandakumar, Chintalapudi, Padmanabhan and Venkatesan @cite_29 have presented a study on acoustic peer-to-peer near-field-communication (up to 15-20 cm), where eavesdropping by third parties is prevented by the means of signal jamming. Based on the concept of audio networking, we construct a wireless mesh network, not with the ambition to compete with wireless communication standards, but to prove that covert and stealthy communication is possible with audio networking and that critical information can be leaked over a covert acoustical mesh network.