Abstract. When cryptosystems are being used in real life, hardware and software implementations themselves present a fruitful field for attacks. Side channel attacks exploit information such as time measurements, power consumption and electromagnetic emission that leaks from a device when it executes cryptographic applications. When leaked information is correlated to a secret key an adversary may be able to recover the key by monitoring this information. This paper describes an AES coprocessor that provides complete protection against power analysis attacks by embedding data masking at a hardware level.