Securing SCADA systems is a critical aspect of Smart grid security. As sophisticated attacks continue to target industrial systems, the focus should be on planning and developing new security techniques that will adapt to the SCADA environment and protocols. Traditional SCADA protocols such as DNP3, Modbus and ICCP do not support encryption, authentication and data integrity in their native form. Although they can be secured with VPN tunnels, IPSEC adds significant network overhead and complexity to the end hosts. SCADA devices may lack the computing resources to implement this kind of technique. In this thesis, a security design is proposed that can help make communications between the master stations and slave devices in a SCADA network secure without putting additional overhead on the remote devices. This research designs a SCADA Security Device (SSD), which can work in conjunction with other network elements to implement a secure architecture for SCADA protocols. Several components of the SSD were implemented and tested during this research to evaluate the security features in a SCADA network.