As industrial control systems (ICSs) have become increasingly connected and use more off-the-shelf components, new vulnerabilities to cyber attacks have emerged. This paper looks at three types of ICSs: programmable logic controllers (PLCs), supervisory control and data acquisition (SCADA) systems, and distributed control systems (DCSs), and then discusses security issues and remedies. This document also explains the benefits and limitations of two cryptographic solutions (digital signatures and encryption) and elaborates on the reasons for using security ICs in an ICS to support cryptography.