The requirement and benefits of off-the-shelf technologies and open standards makes the industrial automation and control systems (IACS) to move from isolated environment to interconnect with other networks. This makes the industrial control systems to expose for wide range of cyber attacks. As the severity of the cyber attacks on these networks are increasing, adopting crypto techniques and securing the industrial plant is a high priority issue from the past few years. The integration of crypto technologies in IACS is successful only by an effective key management infrastructure (KMI). From IACS perspective, this paper addresses the challenges and parameters that need to be considered while designing a KMI for IACS. Also, case study on KMI issues for supervisory control and data acquisition (SCADA) and WirelessHART is discussed. By considering the constraints and required key management features, an efficient key management scheme is proposed for SCADA and WirelessHART using polynomial key establishment scheme.