  Information flows are intrinsic properties of an multi-stage manufacturing
systems (MMS). In computer security, a basic information flow tracking
technique is dynamic taint analysis (DTA). DTA tracks taint propagation from
one data variable (e.g., a buffer holding a HTTP request) to another. Taint
propagation paths are typically determined by data flows and implicit flows in
a computer program. And the union of all the taint propagation paths forms a
taint graph. It is clear that taints graphs could significantly enhance
intrusion diagnosis. However, the existing DTA techniques cannot be directly
used in an MMS, and a main reason is as follows: Without manufacturing-specific
taint propagation rules, DTA cannot be implemented. In this work, we conduct a
case study which (a) extends the existing DTA method with
manufacturing-specific taint propagation rules, and (b) applies the extended
method to perform preliminary intrusion diagnosis with a small-scale test-bed.
