Declassification occurs when the confidentiality of information is weakened; erasure occurs when the confidentiality of information is strengthened, perhaps to the point of completely removing the information from the system.

This paper shows how to enforce erasure and declassification policies. A combination of a type system that controls information flow and a simple runtime mechanism to overwrite data ensures end-to-end enforcement of policies. We prove that well-typed programs satisfy the semantic security condition noninterference according to policy.

We extend the Jif programming language with erasure and declassification enforcement mechanisms and use the resulting language in a large case study of a voting system.