Start Network devices are generally programmed over the serial ports (COM-RS232) or over the network via telnet protocol or ssh protocol. The communication process via the Telnet protocol and COM port is done unencrypted. Therefore, there is a possibility to listen and change the communication by an intervening hacker. In order to prevent this, the hardware is designed described below. With this developed system, serial communication has been encrypted by adding RSA encryption using hardware between network devices which needs configuration with PC.