Authentication based on a combination of multiple and unrelated identifiers provides the strongest access control, for example, the use of both a digital and a physical key, such as a password and a biometric scanner. Another example may include the use of dedicated hosts for specific functions. The specific purpose of each ICS component under evaluation must be considered, and account for unique operational requirements of each. It may be possible to implement strong, multifactor authentication at an Engineering Workstation, where this may not be acceptable at an Operator HMI that depends on shared operator accounts.
Shared operator accounts should not be allowed on such critical system, this approach breaches CIA principals, there is no way to identify who access the system, audit and we get a problem of repudiation.
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