DPA on Faulty Cryptographic Hardware and Countermeasures

Balanced gates are an effective countermeasure against power analysis attacks only if they can be guaranteed to maintain their power balance. Traditional testing and reliability methods are used primarily only to ensure the correctness of the logical functionality and not the balance of a circuit. Due to the hardware redundancy in balanced gate designs, there are many faults which can imbalance a balanced gate without causing logical errors. As a result, traditional testing and reliability methods and architectures are unable to test and verify if a gate is completely defect and fault-free and hence balanced. Our simulations show that a few faulty balanced gates can make a circuit as vulnerable to power analysis attacks as a completely imbalanced implementation. This vulnerability opens the possibility of new methods of attacks based on a combination of fault and power attacks. A solution to the vulnerability based on a built-in differential self-balance comparator is presented.