Data authentication and integrity are predominant factors that determine the reliability and security of a communication system. The integration of computers and communication capabilities with power systems, digitization, and massive deployment of Information and Communication Technology (ICT) systems have rendered the systems more vulnerable to unauthorized intrusions into the digital substations. Hence, cyber security has become the most up surging challenge in electrical power systems. This paper discusses various security challenges on Sampled Value (SV) message and develops robust algorithms to mitigate them. It proposes the implementation of Message Authentication Code (MAC) enabled SV to secure the process bus network in the substation automation system (SAS) in a power grid. Also, a structured analysis of the performance of SV stream transmission between Merging Units (MU) and protection and control (P&C) intelligent electronic devices (IEDs) in a digital substation pertaining to timing specifications and feasibility is presented.