Programs trusted with secure information should not release that information in ways contrary to system policy. However, when a program contains an illegal flow of information, current information-flow reporting techniques are inadequate for determining the cause of the error. Reasoning about information-flow errors can be difficult, as the flows involved can be quite subtle. We present a general model for information-flow blame that can explain the source of such security errors in code. This

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... odel is implemented by changing the information-flow verification procedure to: (1) generate supplementary information to reveal otherwise hidden program dependencies; (2) modify the constraint solver to construct a blame dependency graph; and (3) develop an explanation procedure that returns a complete and minimal error report. Our experiments show that information-flow errors can generally be explained and resolved by viewing only a small fraction of the total code.