Abstract-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.

This article estimates the costs of school finance adequacy in each of the 50 states and Washington, D.C. by applying the recommendations from an evidence-based model to the student characteristics of each individual state. Using two different prices, (a) the national average teacher salaries adjusted by a comparable wage index and (b) individual state teacher salaries, the authors estimate per pupil costs of adequacy. Results suggest that in 30 states additional resources are needed to reach the funding level for the evidence-based model. The findings do not make adjustments for diseconomies resulting from large numbers of small schools or districts or other state preferences for educational services that could lead to individual state variations from the authors' findings.

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In this randomized field trial of KindergARTen Camp, a 6-week summer enrichment program in literacy and the fine arts, we analyzed the summer learning outcomes of 93 treatment and 35 control students from high-poverty schools in Baltimore, Maryland. This experiment offers evidence concerning the causal effect of the program on 5 measures of students' literacy achievement. We found treatment effects during the summer months that were of both practical and statistical significance on the Developmental Reading Assessment (DRA) and the Word List A assessments. In addition, results from surveys of KindergARTen Camp students, parents, and teachers revealed strong satisfaction with the program. We conclude by discussing the contextual factors that may have contributed to these results.

In this paper, we discuss the performance of multi-path routing techniques in underwater acoustic networks applied to an intruder detection scenario. We assume that a network of submarine sensors is deployed close to a surveilled harbor, with the task to detect outbound surface boats. The communications take place in the 4 to 8 kHz band, in order to favor long-haul transmissions. This band is highly affected by the noise originating from the boat propellers. Therefore, we resort to jamming-resilient techniques such as multi-path transmissions. The latter is accomplished by restricted flooding, and by an adaptive form of source routing as an alternative. Our results show that the inherent redundancy of multi-path routing offers an effective shield against excessive packet losses in the presence of strong jamming. This increases the probability that data packets containing detection information are promptly delivered to the desired sinks, with respect to the performance of static, single-path routing. In particular, restricted flooding achieves the best delivery ratio at the price of a very high number of generated replicas, whereas adaptive source routing trades off a lower delivery ratio for a lower overhead