Secure information flow guarantees the secrecy and integrity of data, preventing an attacker from learning secret information (secrecy) or injecting untrusted information (integrity). Covert channels can be used to subvert these security guarantees; for example, timing and termination channels can, either intentionally or inadvertently, violate these guarantees by modifying the timing or termination behavior of a program based on secret or untrusted data. Attacks using these covert channels have been published and are known to work in practice—as techniques to prevent non-covert channels are becoming increasingly practical, covert channels are likely to become even more attractive for attackers to exploit. The goal of this paper is to understand the subtleties of timing- and termination-sensitive noninterference, explore the space of possible strategies for enforcing noninterference guarantees, and formalize the exact guarantees that these strategies can enforce. As a result of this effort we create a novel strategy that provides stronger security guarantees than existing work, and we clarify claims in existing work about what guarantees can be made
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