As fieldbus networks are becoming accessible from the Internet, security mechanisms to grant access only to authorized users and to protect data are becoming essential. This paper proposes a formally-based approach to the analysis of such systems, both at the security protocols level, and at the system architecture level. This multi-level analysis allows the evaluation of the effects of an attack on the overall system, due to security problems that affect the underlying security protocols. A case study on a typical fieldbus security system validates the approach.
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