Latchup is a short-circuit that can be triggered in CMOS ICs when a current pulse is produced by parasitic perturbations. It is usually regarded as very disturbing for reliability, especially in space applications where it is triggered by ionizing particles naturally present in the environment. But in another context, the one of crypto-processors, it could be used as a way to protect the device from attacks by fault injections. Indeed, if all the parts of the ICs containing the secret data have the property to be more sensitive to latchup than to upsets, it will be impossible for attackers to retrieve the key with fault injections attacks. This paper describes how to design a crypto-processor with such features, and how to verify its properties.