Approaches for Inaudible Acoustic Communication

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Zhang, B., Zhan, Q., Chen, S., Li, M., Ren, K., Wang, C., & Ma, D. (2014). PriWhisper: Enabling Keyless Secure Acoustic Communication for Smartphones. IEEE Internet of Things Journal, 1(1), 33-45. Short-range wireless communication technologies have been used in many security-sensitive smartphone applications and services such as contactless micro payment and device pairing. Typically, the data confidentiality of the existing short-range communication systems relies on so-called “key-exchange then encryption” mechanism. Namely, both parties need to spend extra communication to establish a common key before transmitting their actual messages, which is inefficient, especially for short communication sessions. In this work, we present PriWhisper — a keyless secure acoustic short-range communication system for smartphones. It is designed to provide a purely software-based solution to secure smartphone short-range communication without the key agreement phase. PriWhisper adopts the emerging friendly jamming technique from radio communication for data confidentiality. The system prototype is implemented and eval-uated on several Android smartphone platforms for efficiency and usability. We theoretically and experimentally analyze the security of our proposed acoustic communication system against various passive and active adversaries. In particular, we also study the (in)separability of the data signal and jamming sig-nal against Blind Signal Segmentation (BSS) attacks such as Independent Component Analysis (ICA). The result shows that PriWhisper provides sufficient security guarantees for commercial smartphone applications and yet strong compatibilities with most legacy smartphone platforms The Pre-Whisper project realizes novel NFC approaches for smartphones (among others with audio)

Edwards, Alexander Orosz, "Ultrasonic Data Steganography" (2016). Honors College Capstones and Theses. 5. What started off as a question on the possibly of data transmission via sound above the level of human hearing evolved into a project exploring the possibility of ultrasonic data infiltration and exfiltration in an information security context. It is well known that sound can be used to transmit data as this can be seen in many old technologies, most notably and simply DTMF tones for phone networks. But what if the sound used to transmit signals was in in the ultrasonic range? It would go generally unnoticed to anyone not looking for it with tools such as a spectrum analyzer. This could provide an unnoticed means of transmitting overhead data without the use of radio signals or physical connections, or, more clandestinely, a means to inject or retrieve data virtually undetect ed for espionage, control, or other malicious activity. As expected, there would obviously be issues with signal quality as the open air is heavy with environmental interference, but in specific cases as seen in the following research, a discrete sonic means of data transmission may not only be practical, but necessary for the task at hand.

This project is an exploration of the practicality of ultrasonic data transmission between computers. It will include research into the topic in general from scientific, technological, and security perspectives. There will be inclusions from other research projects as well as practical applications already in existence. Interestingly, there are already some suspected, but unconfirmed planned systems as well security incidents using this technology. Finally, a short seriesof semi-formal (in a scientific sense) experiments conducted to provide firsthand accounts and results of the ultrasonic data transmission concept

A hands-on report on the development of an ultrasound communication approach. Related work is presented and problems of the technology are pointed out.
Arentz, W. A., & Bandara, U. (2011). Near ultrasonic directional data transfer for modern smartphones (p. 481). ACM Press. The rapid advancements in the smartphone domain has made WiFi, Bluetooth and 3G commonplace in most devices, as well as accelerometers, gyros, fast CPUs and large amounts of memory. During these advancements the IR transmitter was eventually dropped, starting perhaps most importantly with the release of the Apple iPhone. It has since been observed a need for directional transmission functionality. The system described herein propose a way to to achieve short range directional data-communication on a smartphone without adding external hardware. The outcome of this project is intended to be open-sourced, enabling any application developer or phone-manufacturer to include the technology into their products. A feasibility study on ultrasonic communication between smartphones

Low technical complexity

Frequency band: 20-23kHz

Modulation: pulsed signal (short pulse=0, long pulse=1)

They indended to make their software open source (in 2011)
Lazik, P., Rajagopal, N., Shih, O., Sinopoli, B., & Rowe, A. (2015). ALPS: A Bluetooth and Ultrasound Platform for Mapping and Localization (pp. 73–84). ACM Press. The proliferation of Bluetooth Low-Energy (BLE) chipsets on mobile devices has lead to a wide variety of user-installable tags and beacons designed for location-aware applications. In this paper, we present the Acoustic Location Processing System (ALPS), a platform that augments BLE transmitters with ultrasound in a manner that improves ranging accuracy and can help users configure indoor localization systems with minimal effort. A user places three or more beacons in an environment and then walks through a calibration sequence with their mobile device where they touch key points in the environment like the floor and the corners of the room. This process automatically computes the room geometry as well as the precise beacon locations without needing auxiliary measurements. Once configured, the system can track a user's location referenced to a map.

The platform consists of time-synchronized ultrasonic transmitters that utilize the bandwidth just above the human hearing limit, where mobile devices are still sensitive and can detect ranging signals. To aid in the mapping process, the beacons perform inter-beacon ranging during setup. Each beacon includes a BLE radio that can identify and trigger the ultrasonic signals. By using differences in propagation characteristics between ultrasound and radio, the system can classify if beacons are within Line-Of-Sight (LOS) to the mobile phone. In cases where beacons are blocked, we show how the phone's inertial measurement sensors can be used to supplement localization data. We experimentally evaluate that our system can estimate three-dimensional beacon location with a Euclidean distance error of 16.1cm, and can generate maps with room measurements with a two-dimensional Euclidean distance error of 19.8cm. When tested in six different environments, we saw that the system can identify Non-Line-Of-Sight (NLOS) signals with over 80% accuracy and track a user's location to within less than 100cm.

Extend BT LE Beacons with ultrasound to improve ranging accuracy

Focus: estimate 3D location of a beacon relative from a smartphone (by using BT and ultrasonic sound)

This enables indoor localization and tracking
Lazik, P., & Rowe, A. (2012). Indoor pseudo-ranging of mobile devices using ultrasonic chirps (p. 99). ACM Press. In this paper, we present an indoor ultrasonic location tracking system that can utilize off-the-shelf audio speakers (potentially already in place) to provide fine-grained indoor position data to modern mobile devices like smartphones and tablets. We design and evaluate a communication primitive based on rate-adaptive wide-band linear frequency modulated chirp pulses that utilizes the audio bandwidth just above the human hearing frequency range where mobile devices are still sensitive. Typically transmitting data, even outside of this range, introduces broadband human audible noises (clicks) due to the non-ideal impulse response of speakers. Unlike existing audio modulation schemes, our scheme is optimized based on psychoacoustic properties. For example, all tones exhibit slowly changing power-levels and gradual frequency changes so as to minimize human perceivable artifacts. Chirps also bring the benefit of Pulse Compression, which greatly improves ranging resolution and makes them resilient to both Doppler shifts as well as multi-path propagation that typically plague indoor environments. The scheme also supports the decoding of multiple unique identifier packets being transmitted simultaneously. By applying a Time-Difference-of-Arrival (TDOA) pseudo-ranging technique the mobile devices can localize themselves without tight out-of-band synchronization with the broadcasting infrastructure. This design is not only scalable with respect to the number of transmitters and tracked devices, but also improves user privacy since the mobile devices compute their positions locally. We show through user studies and experimentation on smartphones that we are able to provide sub-meter (95% < 10cm) accurate indoor positioning in a manner that is imperceptible to humans. Acoustic indoor tracking system with normal speakers (in ultrasound band)

Modulation: chirp pulses

Localization by time of flight measurements
Murata, S., Yara, C., Kaneta, K., Ioroi, S., & Tanaka, H. (2014). Accurate Indoor Positioning System Using Near-Ultrasonic Sound from a Smartphone (pp. 13–18). IEEE. This paper describes new concepts and techniques for an indoor positioning system that uses near-ultrasonic sound from a smartphone. The indoor positioning system can be used in many practical applications, for example, in detecting the location of moving objects, such as a person or a wheelchair, and navigation within a wide indoor area. Indoor positioning systems seem to require a higher positioning accuracy compared with systems for use in outdoor areas. The authors have previously proposed a solution for indoor positioning using ultrasonic sensors. However, these suffer from a shortcoming in that users have to possess a special ultrasonic transmitter. The system proposed here does not need such a transmitter, because a smartphone is used as the sound source. Smartphones are already widely used, so the proposed system seems to be easy to introduce for practical use. The sound transmitted from the smartphone has been investigated and confirmed, as has the validity of the developed receiving unit which makes use of the timer count values of a microcomputer, which gives an indication of the timing of the detection of sound from the smartphone. Positioning tests for static and moving objects have been carried out in both quiet and noisy environments. It has been verified that the positioning accuracy is sufficient for navigation for visually impaired persons and for other applications. Indoor tracking system based on ultrasound that is sent from a smartphone

Several receiving units in the room detect the ultrasonic signal from the user
Santagati, G. E., & Melodia, T. (2015). U-Wear: Software-Defined Ultrasonic Networking for Wearable Devices (pp. 241–256). ACM Press. Wearable medical sensing devices with wireless capabilities have become the cornerstone of many revolutionary digital health applications that promise to predict and treat major diseases by acquiring and processing health information. Existing wireless wearable devices are connected through radio frequency (RF) electromagnetic wave carriers based on standards such as Bluetooth or WiFi. However, these solutions tend to almost-blindly scale down traditional wireless technologies to the body environment, with little or no attention to the peculiar characteristics of the human body and the severe privacy and security requirements of patients. We contend that this is not the only possible approach, and we present U-Wear, the first networking framework for wearable medical devices based on ultrasonic communications.

U-Wear encloses a set of physical, data link and network layer functionalities that can flexibly adapt to application and system requirements to efficiently distribute information between ultrasonic wearable devices. U-Wear also offers reconfiguration functionalities at the application layer to provide a flexible platform to develop medical applications. We design two prototypes that implement U-Wear and operate in the near-ultrasonic frequency range using commercial-off-the-shelf (COTS) speakers and microphones. Despite the limited bandwidth, i.e., about 2 kHz, and COTS audio hardware components not optimized for operating at high frequency, our prototypes (i) achieve data rates up to 2.76 kbit/s with bit-error-rate lower than 10-5 using a transmission power of 20 mW; (ii) enable multiple nodes to share the medium; and (iii) implement reconfigurable data processing to extract medical parameters from sensors with high accuracy.

A networking solution for wearable medical devices based on ultrasonic communication is presented

The prototype uses a Teensy 3.1 board, a small MEMS microphone and a COTS speaker
Thiel, B., Kloch, K., & Lukowicz, P. (2012). Sound-based proximity detection with mobile phones (pp. 1–4). ACM Press. We present a method for proximity detection with mobile phones that is based on a combination of Bluetooth communication (for the detection of coarse proximity) and sound beacons in an inaudible spectrum around 18kHz for a finer spatial resolution. The system performs a real-time recognition of personal encounters in two common situations: standing together and walking by each other. We evaluate our approach in a variety of settings ranging from office corridor, through a busy street to a shopping mall. Combination of BT and ultrasonic information for distance estimation

Modulation: on-off keying
Yi, W.-J., Gilliland, S., & Saniie, J. (2013). Mobile ultrasonic signal processing system using Android smartphone (pp. 1271–1274). IEEE. This study introduces a mobile ultrasonic signal processing (MUSP) system using an Android smartphone for remote ultrasonic testing and imaging applications. The Android smartphone has multiple wireless data communication options such as Bluetooth, Wi-Fi and cellular data networks. The smartphone receives the ultrasonic data using the Bluetooth connection from a data acquisition and communication unit (DACU). With the help of Android Native Development Kit (NDK) libraries, we developed two signal processing algorithms in C programming language which are processed by the Android smartphone to explore the smartphone computing capability for ultrasonic testing applications. Split Spectrum Processing (SSP) and Chirplet Signal Decomposition (CSD) algorithms are considered for benchmarking and signal analysis. The analyzed data is displayed in real-time on the smartphone screen and streamed to a central location via Wi-Fi or cellular data networks for storage and further data analysis. A Java programmed server application is implemented to communicate with the Android application over the Internet in order to display and save the retrieved signal data. This system brings the ability to analyze ultrasonic signals remotely and to transfer ultrasound data from one end to the other for extensive signal ultrasonic imaging at a central location. The accessibility of the ultrasonic data at the central location allows experts to review ultrasonic information and make decision about the state of the health of structures and critical components under test. Two ultrasonic sound descomposition schemes are implemented on an Android platform. The ultrasonic data, however, is sent via BT to the phone. It is then decomposed on the phone.
Vasilios Mavroudis, Shuang Hao, Yanick Fratantonio, Federico Maggi, Christopher Kruegel, and Giovanni Vigna On the Privacy and Security of the Ultrasound Ecosystem Nowadays users often possess a variety of electronic devices for communication and entertainment. In particular, smartphones are playing an increasingly central role in users’ lives: Users carry them everywhere they go and often use them to control other devices. This trend provides incentives for the industry to tackle new challenges, such as cross-device authentication, and to develop new monetization schemes. A new technology based on ultrasounds has recently emerged to meet these demands. Ultrasound technology has a number of desirable features: it is easy to deploy, flexible, and inaudible by humans. This technology is already utilized in a number of different real-world applications, such as device pairing, proximity detection, and cross-device tracking. This paper examines the different facets of ultrasound-based technology. Initially, we discuss how it is already used in the real world, and subsequently examine this emerging technology from the privacy and security perspectives. In particular, we first observe that the lack of OS features results in violations of the principle of least privilege: an app that wants to use this technology currently needs to require full access to the device microphone. We then analyse real-world Android apps and find that tracking techniques based on ultrasounds suffer from a number of vulnerabilities and are susceptible to various attacks. For example, we show that ultrasound cross-device tracking deployments can be abused to perform stealthy deanonymization attacks (e.g., to unmask users who browse the Internet through anonymity networks such as Tor), to inject fake or spoofed audio beacons, and to leak a user’s private information.