Optical Fault Attacks on AES: A Threat in Violet

Microprocessors are the heart of the devices we rely on every day. However, their non-volatile memory, which often contains sensitive information, can be manipulated by ultraviolet (UV) irradiation. This paper gives practical results demonstrating that the non-volatile memory can be erased with UV light by investigating the effects of UV-Clight with a wavelength of 254 nm on four different depackaged microcontrollers. We demonstrate that an adversary can use this effect to attack an AES software implementation by manipulating the 256- bit S-box table. We show that if only a single byte of the table is changed, 2 500 pairs of correct and faulty encrypted inputs are sufficient to recover the key with a probability of 90%, in case the key schedule is not modified by the attack. Furthermore, we emphasize this by presenting a practical attack on an AES implementation running on an 8-bit microcontroller. Our attack involves only a standard decapsulation procedure and the use of alow-cost UV lamp.