Fault induction attacks are a serious concern for designers of secure embedded systems. An ideal solution would be a generic circuit transformation that would produce circuits that are robust against fault induction attacks. We develop a framework for analyzing the security of systems against single fault attacks and apply it to a recent proposed method (dual-rail encoding) for generically securing circuits against single fault attacks. Ultimately, we find that the method does not hold up under our threat models: n-bit cryptographic keys can be extracted from the device with roughly n trials. We conclude that secure designs should incorporate explicit countermeasures to either directly address or attempt to invalidate our threat models.