Speech Scrambling Based on Imitation of a Target Speech Signal with Non-confidential Content

This paper shows a new approach of speech scrambling using imitation to produce a scrambled speech signal with intelligible content. The secret message imitates a target speech signal with non-confidential content through an adaptation mechanism. Unlike the classical approach, the key is not an input of the system because it is created in the adaptation process. Several tests are conducted in order to validate adaptation as an efficient key generator, and the robustness of the scrambled speech signal against signal manipulation attacks. The advantages of our proposal are (1) the scrambled speech signal is an intelligible speech signal so that it does not generate suspicious about the existence of the secret message, (2) the system does not require an external key generator because the elements are permutated according to the adaptation process, (3) the length of the key is long enough so that it guarantees that the key is not found by brute-force attack, and (4) it works with perfect secrecy because the a priori probability of the secret message is the same as the a posteriori probability, given the scrambled speech signal.