Highly Robust Covert Information Transmission Based On Pitch Delay Over Voice Channels

With the continuous development of mobile communication networks,the quality of end-to-end communication has been further improved,and the transmission rate and coverage have been greatly improved.Email,telephone,SMS and other means of information exchange,these modes of information transmission to the public’s production and life have brought a lot of convenience.However,information leakage,theft and other security risks can’t be ignored in the transmission of information,so that the information before entering the mobile terminal by the third-party malicious theft.Although the mobile communication system standard contains many security protection mechanisms,it often has little effect.How to make use of the convenience of mobile communication network while effectively protecting the safe transmission of data has become an urgent issue to be solved.This paper makes full use of the advantages of high quality,high priority and low delay in the mobile voice channel,combines with the analysis of the transmission characteristics of the mobile voice channel,and proposes an information transmission scheme based on pitch delay steganography to solve the problems existing in the existing information transmission algorithms.In order to further improve the transmission rate of secret information,a voice-like modulation scheme based on pitch delay is proposed.The main research work and innovation of this paper are as follows:(1)Aiming at the problem that the previous steganographic embedding algorithms are difficult to adapt to 4G/5G network transmission,this paper proposes a low bit rate steganographic algorithm for audio information which imparts secret information into the pitch delay characteristics of voice.The program hides the target data in the voice signal.In this algorithm,the parity of pitch delay of voiced part is embedded respectively,while the pitch delay of voiceless part is quantized to embed hidden information.The slight change in pitch delay caused by embedding does not result in a significant degradation of the original sound quality.Therefore,when transmitting such voice signals,it is difficult for the outside world to detect hidden data information.The algorithm can ensure the security and privacy of the end-to-end communication.In addition,the carrier of extracting secret information is audio,which can pass through the adaptive bit rate network smoothly and recover information correctly at the receiving end.Under simulation test,the transmission rate of secret information can reach 200bps,and the accuracy rate is about 93%.(2)Based on the characteristic that voice pitch delay is stable over voice mobile and the principle of vocoder decoding in channel transmission,an information transmission scheme based on voice pitch delay is proposed.By preprocessing the corpus space,a series of speech fragments with similar pitch delay are selected to enter the code word space to be selected.The cyclic iterative algorithm is adopted to continuously optimize the codebook space,and the code word set with large difference in time domain is screened.The secret information is mapped to each code word in the constructed set to generate a voice signal,which is transmitted endto-end through the channel.The secret information is recovered by decoding at the receiving end.In the simulation test,when the information transmission rate is 1kbps,the average bit error rate can reach 10-5.