A Study Of Encryption Technology Based On The Analog Voice

In recent years, with the development of communication networks and improvement of mobile communication technology, the communication devices, such as mobile phone and so on, have a more widely applications in human’s daily lives. For the voice is the most important information on the mobile communication transmission network, the voice security issue happens in the transmission process has aroused more and more attention. In traditional voice transmission system, the voice is encrypted by the existing safe mechanisms in mobile communication protocols. Moreover, the encryption is optional and controlled by the network operator. With increasing business volume, the mobile communication system become more complex, and some kernel encryption algorithms have been cracked, which make the original safe mechanisms and user to user communication unsafe. Then, for guaranteed end-to-end security, the speech signal must be encrypted before entering the communications system, and the encryption key should be mastered by users. Based on the analysis of GSM communication workflow and RPE-LTP vocoder characteristics, this paper implements the study and design of end-to-end voice encryption system via simulation. The author’s major contributions are outlined as follows:1. On the basis of analyzing GSM voice transmission system, RPE-LTP coding theory, and three basic conditions that the transmission of encrypted voice on mobile voice channel should meet: the encrypted voice should meet the input requirement of the vocoder, the encrypted voice is not sensitive to the lossy compression and the encrypted voice is not touch off the VAD detection, this paper finished the theoretical analysis of the encryption algorithm and present a voice encryption scheme, so that the encrypted voice will not be clearly distorted by the vocoder.2. An algorithm of voice encryption based on the analog voice is presented. First of all, the algorithm samples,frames and groups the analog voice. Then, the voice signal is transformed into frequency domain, and for the realization of voice frequency encryption. frequency domain of the voice signal is scrambled. Finally, the voice signal is transformed into time domain and the order of frames in a group is scrambled.Consequently, encrypted voice is obtained, which can be directly transmitted on mobilevoice channel. In transmitting end, a false spectrum can also be inserted into the spectrum of the voice signal in order to “confuse” the spectrum of original signal. In receiving end, the encrypted voice, which has been decoded, is decrypted according to the inversion of encryption process. The algorithm directly encrypts the analogy voice,which can against the lossy compression used in the mobile communication and ensure better end-to-end secure communications over GSM voice channel.3. This paper designs and implements a simulation platform of end-to-end voice encryption system. Based on the platform, an experiment of secure voice transmission is carried on successfully and a analysis is made of experimental results. Experimental results verify the effectiveness of the encryption algorithm and the feasibility of end-to-end voice encryption system.