Research On End-To-End Voice Encryption And Transmission Technology For Mobile Communication

Recent years, with the popularization of mobile communication service, cellphone and other mobile terminal devices has been widely used in our lives. However, people are facing the nonignorable secure problems of voice call while enjoying its convenience. Eavesdropping is one of the most common secure problems. Now, with the improvement of people’s safety awareness, security of mobile communication has become a research hotspot in the information security field. Some measures, like the overall transformation, redesign of mobile communication networks and transformation of mobile devices, are all common in various mobile communication security schemes. End-to-end voice encryption scheme which is implemented on mobile devices has become a research hotspot today. Because it is simple and cheap to realize. End-to-end voice encryption and transmission is studied in this paper by studying related theories, designing schemes and conducting experiments.First, after introducing the transmission characteristics of mobile voice networks by studying various vocoder standards and VAD techniques, demand analysis of end-to-end voice encryption and transmission is done.Second, an encryption scheme based on modifying the shape of voice frequency spectrum is proposed. Several voice short-term characteristic parameters are studied. A syllable division method based on these parameters is designed to assist encryption. After reaserching the frequency spectrum shape and distribution features, a modification method is designed and simulation experiment is done.The method is proved to be effective and encrypted voice can be transmitted in the mobile voice channel.Third, after studying voice compression encoding and stream encryption algorithm, a scheme is proposed, which is based on stream encryption of the compressed voice data and transmission using OFDM modulation. Corresponding OFDM symbol structure and parameter are designed after researching and testing the transmission channel using GSM FR vocoder. They are designed for the purpose of making encrypted signal to be transmitted stably and effectively. After completing simulation experiment based on the proposed method, demodulation bit error rates under different modulation methods are compared. The demodulation bit error rate of transmission signal generated by QPSK is analyzed under the condition of GSM EFR vocoder. A method of chaning signal frequency is proposed. Also the demodulation bit error rate under different code rate is tested in the channel using AMR vocoder.