Study And Implementation Of Analog Telephone Secure Communication Device Based On DSP

Telephone communication is the communication mode of information exchange that is in the manner of speech. Speech information security has become more important with the development of information technology and secure communication has gained broad attention. In order to implement the secure speech transmission, in the traditional digital secure communication method, an encryption and a decryption devices are placed at the originator and recipient sides, respectively. However, the traditional method has some problems such as the key agreement and replacement. To eliminate the problems, an analog telephone secure communication device based on DSP was designed and implemented in this paper. The following three main aspects of the work were implemented:(1) On the basis of secure speech transmission demand, a new scheme for secure analog telephone communication was given. In this scheme, the only secure communication device was placed on the recipient side. A backward homology sound-based method for speech signal interference was used to scramble the speech signal from the originator in order to transmit the speech signal from the originator securely. At the same time, an anti-sidetone function of analog telephone was used to shield the scrambling signal to recover the original speech signal. Therefore, the recipient could receive the original speech signal from the originator without an extra descrambling device.(2) A hardware platform of the device was designed as two parts:the basic circuits, including power, clock, reset and JTAG modules and the functional circuits, including normal communication, scrambling communication, speech acquisition, speech scrambling and speech control modules.(3) Hardware-software joint debugging and function test of the secure analog telephone communication device were implemented. The feasibility of this device was verified according to the speech oscillogram. Experiments were conducted that verified the secure effect in secure speech application fields. The results and analyses indicated that this device had a good secure effect for different kinds of speech contents.