Development Of Encryption System For Phone And Fax

In recent years, the telephone and the fax have been widely used. The communication security has gradually been a problem for their development. In this text, the design and application of a system that encrypt speech signal or the fax data is discussed.Aiming at the safety of telephone communication, a telephone encrypt system based on 3DES algorithm is described in this paper. The single chip is used as the central control unit and FPGA is used to encrypt and decrypt the data. The computer's serial interface is used to download and change the secret key. The secret key of the system is 256-bit, and can be changed continuously. With this system, the problem of voice data being stolen can be solved. This telephone encrypt system has been implemented successfully and performs well, and can be used widely.The encryption of telephone and fax is achieved through transmitting the encrypted digital signal of telephone and fax. For telephone encryption, at the transmitter, analog voice signal, form microphone, is changed to digital signal and then it is compressed, encrypted and sent to the receiver by modem. At the receiver, information is decrypted and decompressed. And finally it is converted to the analog voice signal to drive the telephone handset. For fax encryption, data received by fax modem from fax is encrypted and tranmitted to the receiver. At the receiver, data is decrypted and sent to fax by fax modem.The system has been validated on the PSTN (Public Switched Telephone Network). It is indicated that the voice transmitted is clear and that the quality and the speed of the fax is ensured. It won't affect the work of the telephone or the fax.