Secure speech communication over public switched telephone network

This paper is incorporated to explain the work to design a secure telephone prototype namely "SecurePhone", with practical and reliable encryption, easy to operate and connects to public switched telephone networks (PSTN). SecurePhone is a device terminal that is designed to operate reliably, with high speech quality. It can acts as both ordinary telephones and secure instruments over the dial-up PSTN. Secure telephone operates in full duplex over a single telephone circuit using echo cancelling modem technology.