Article
Synchronization of Acoustic Signals for
Steganographic Transmission
Jarosław Wojtu ´n * and Zbigniew Piotrowski
Citation: Wojtu ´n, J.; Piotrowski, Z.
Synchronization of Acoustic Signals
for Steganographic Transmission.
Sensors 2021, 21, 3379. https://
doi.org/10.3390/s21103379
Academic Editors: Nikolaos Thomos
and Eirina Bourtsoulatze
Received: 1 April 2021
Accepted: 5 May 2021
Published: 12 May 2021
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Faculty of Electronics, Military University of Technology, 00-908 Warsaw, Poland;
zbigniew.piotrowski@wat.edu.pl
* Correspondence: jaroslaw.wojtun@wat.edu.pl
Abstract:
Steganography is a technique that makes it possible to hide additional information (pay-
load) in the original signal (cover work). This paper focuses on hiding information in a speech
signal. One of the major problems with steganographic systems is ensuring synchronization. The
paper presents four new and effective mechanisms that allow achievement of synchronization on the
receiving side. Three of the developed methods of synchronization operate directly on the acoustic
signal, while the fourth method works in the higher layer, analyzing the structure of the decoded
steganographic data stream. The results of the research concerning both the evaluation of signal
quality and the effectiveness of synchronization are presented. The signal quality was assessed based
on both objective and subjective methods. The conducted research confirmed the effectiveness of the
developed methods of synchronization during the transmission of steganographic data in the VHF
radio link and in the VoIP channel.
Keywords: audio steganography; audio watermarking; security; data hiding; synchronization
1. Introduction
The paper is devoted to the issues of acoustic steganography, and more precisely
hidden synchronization of acoustic steganographic channels. Analyzing scientific pub-
lications in this field, it can be concluded that this is a valid topic, and the algorithms
of acoustic steganography are constantly being improved. However, in many cases, the
authors of the published solutions in their research ignore the significant problem of signal
synchronization, in which data is embedded, often assuming perfect synchronization. In
the case of practical implementations of steganographic systems, this approach is too much
of a simplification, because achieving synchronization is a necessary condition for the
effective extraction of payload [1,2].
Data transmission in a steganographic system is inextricably linked with the issue of
synchronization. In the absence of synchronization mechanisms, the moment of starting
the steganographic data extraction procedure is difficult to determine unequivocally, which
implies the random nature of the received data, which is synonymous with low efficiency
of hidden transmission.
The bit error rate (BER) was adopted as a measure of the efficiency of steganographic
data transmission [
3
]. The use of hidden synchronization methods should therefore result
in obtaining low BER values, which, in combination with detection and correction codes,
will enable error-free transmission of the payload.
The use of hidden synchronization methods may or may not be associated with a
deterioration in the quality of the cover work. Therefore, it is reasonable to search for such
methods of synchronization that will not cause a significant deterioration of the quality of
the signal carrying the payload. We often call cover work (original signal) with a payload
Stego Object or Stego Work [1,2].
The paper presents four unique mechanisms that allow to achieve synchronization
on the receiving side. Three of the developed methods of synchronization operate directly
Sensors 2021, 21, 3379. https://doi.org/10.3390/s21103379 https://www.mdpi.com/journal/sensors
