Secure web access to mini distributed control system

Small distributed control systems with remote web access are becoming fairly common. Sooner or later, security of such systems will become a precondition for some critical applications. However, limited computational power will require some non-standard solu- tions. The paper describes secure web access to a prototype of small distributed control system programmed according to IEC 61131-3 standard. Security is provided by challenge-response authentication of web client and symmetric cryptographic primitives. Communica- tion latency is analysed by means of a Timed Petri Net model.