A novel distortion-tolerant speech encryption scheme for secure voice communication

This paper details a novel distortion-tolerant speech encryption scheme for securing voice communications over digital voice-specific channels such as 3G/4G or VoIP voice calls. The scheme relies on the usual “loudness, pitch and timbre” parametric representation of speech signals but seen as points on various perceptually-continuous manifolds linked by quasi-isometric continuous mappings. The ciphering of the vocal parameters of the initial speech is done by provably-secure, pseudo-random continuous transforms on these manifolds and hence ensures resilience against moderate errors. The enciphered parameters are then re-encoded into a pseudo-speech signal and transmitted over lossy digital voice channels with compression. Upon reception of the distorted pseudo-speech signal, the legitimate receiver retrieves corrupted versions of the initial vocal parameters and reconstructs an intelligible speech signal, perceptually close to the original, using a machine-learning vocoder derived from the LPCNet. The important parts of our scheme are extensively tested through simulations and experiments with encrypted pseudo-speech signals between different mobile phones. Furthermore, we detail a thorough speech quality subjective assessment with a group of 44 participants that demonstrates how the proposed scheme maintains intelligibility with tolerable progressive quality degradation linked to channel distortion. Finally, a preliminary computational analysis is done to justify the feasibility of real-time implementation of our scheme on portable devices. •Speech communication can be secured by scrambling voice into noise-like pseudo-voice.•We propose a novel voice scrambling technique using quasi-isometric transformations on a hypersphere.•The scrambling scheme is provably secure and tolerant to distortion of ciphertexts.•The scheme is evaluated by real-world experiments and speech quality assessments.