Design And Implementation Of High-Frequency Acoustic Covert Communication System

Network security attracts more and more attention due to the wide application of the Internet. Traditionally, a necessary condition of attacks on computers is the data transmission though the wired, wireless, or fiber channel. Thus, if the electronic devices are disconnected to the Internet, the information in them can be considered to be safe. However, there are various unexpected situations for the network security, such as the high-frequency acoustic covert communication technology, which may lead information to be leaked covertly in the absence of the Internet. Therefore, the main interest of this dissertation is to study the high-frequency acoustic covert communication technology and its application in defense and attack of security.This dissertation designs and implements a type of the high-frequency acoustic covert communication systems. The main contributions of this dissertation can be summarized as follows. (1) By investigating the sensitive frequency of human beings and the frequency band supported by common audio hardware, the related data is provided to determine the transmission frequency point and bandwidth employed in the high-frequency acoustic covert communication systems. In details, the frequency point and bandwidth are set as 18kHz and 1kHz, respectively. (2) For the proposed high-frequency acoustic covert communication systems, the designs of communication system diagram, data frame structure, synchronization, modulation/demodulation, and channel coding are elaborated. (3) Based on the actuality of the information and computer security, three application scenarios of the proposed systems are designed, and then, the corresponding security defense measures are provided. (4) The high-frequency acoustic covert communication systems are implemented and the performance is tested in the different transmission distances and the different transmission rates. Specifically, three types of data transmissions are considered, i.e., the bi-node unidirectional covert communication, the bi-node bidirectional covert communication, and the multi-node unidirectional covert communication. Then, in these situations, simulations and experiments are conducted to illustrate the feasibility of the proposed systems.The results in this dissertation show that the high-frequency acoustic covert communication is effective and feasible. The high-frequency acoustic covert communication systems are applicable to the theft and anti-theft of the electronic information in the occasion of close meeting.