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Joint source-cryptographic-channel coding for real-time secure voice communications on voice channels

Abstract : The growing risk of privacy violation and espionage associated with the rapid spread of mobile communications renewed interest in the original concept of sending encrypted voice as audio signal over arbitrary voice channels. The usual methods used for encrypted data transmission over analog telephony turned out to be inadequate for modern vocal links (cellular networks, VoIP) equipped with voice compression, voice activity detection, and adaptive noise suppression algorithms. The limited available bandwidth, nonlinear channel distortion, and signal fadings motivate the investigation of a dedicated, joint approach for speech encodingand encryption adapted to modern noisy voice channels.This thesis aims to develop, analyze, and validate secure and efficient schemes for real-time speech encryption and transmission via modern voice channels. In addition to speech encryption, this study covers the security and operational aspects of the whole voice communication system, as this is relevant from an industrial perspective.The thesis introduces a joint speech encryption scheme with lossy encoding, which randomly scrambles the vocal parameters of some speech representation (loudness, pitch, timbre) and outputs an encrypted pseudo-voice signal robust against channel noise. The enciphering technique is based on random translations and random rotations using lattices and spherical codes on flat tori. Against transmission errors, the scheme decrypts the vocal parameters approximately and reconstructs a perceptually analogous speech signal with the help of a trained neural-based voice synthesizer. The experimental setup was validated by sending encrypted pseudo-voice over a real voice channel, and the decrypted speech was tested using subjective quality assessment by a group of about 40 participants.Furthermore, the thesis describes a new technique for sending data over voice channels that relies on short harmonic waveforms representing quaternary codewords. This technique achieves a variable bitrate up to 6.4 kbps and has been successfully tested over various real voice channels. Finally, the work considers a dedicated cryptographic key exchange protocol over voice channels authenticated by signatures and a vocal verification. The protocol security has been verified in a symbolic model using Tamarin Prover.The study concludes that secure voice communication over real digital voice channels is technically viable when the voice channels used for communication are stable and introduce distortion in a predictable manner.stabintroduce distortion in a predictable manner.
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Submitted on : Friday, October 8, 2021 - 9:45:12 AM
Last modification on : Saturday, October 9, 2021 - 3:48:42 AM

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  • HAL Id : tel-03370542, version 1

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Piotr Krasnowski. Joint source-cryptographic-channel coding for real-time secure voice communications on voice channels. Cryptography and Security [cs.CR]. Université Côte d'Azur, 2021. English. ⟨NNT : 2021COAZ4029⟩. ⟨tel-03370542⟩

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