VoIP steganography and its Detection—A survey
ACM Computing Surveys (CSUR)
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Steganography is used to embed secret messages in cover media. This is especially important in areas where the use of cryptography is prohibited. In this paper we introduce a novel steganographic algorithm applicable for audio data as cover media. The proposed algorithm is based on the phase coding technique which embeds data in the phase spectrum of the frequency domain signal. Differing from previous works we retain the original phase values in order to best keep the quality of the cover audio signal. Secret bits are embedded by introducing a configurable phase difference between selected chunks of blocks from the cover medium instead of discarding the original phase values and introducing a random phase like other approaches. Variable parameters guarantee the security of our system and we show that the wrong selection leads to high reception errors. Also robustness tests were performed using popular signal processing operations like noise addition, cropping and resampling, giving reasonable results. In addition listening tests show that the original audio quality is not noticeable reduced by our algorithm. After pointing out related approaches we highlight our contributions with respect to the embedding and extraction processes. Also a view on the synchronization issue at reception is given. This is a vital part for the steganographic receiver when the communication happens for example over a mobile network. Following to that the results from tests with our working prototype are presented and further usage scenarios in relation to future research are given.