How Microprobing Can Attack Encrypted Memory

This paper exposes some weaknesses of encrypted embedded memory in secure chips. Smartcards and secure microcontrollers are designed to protect confidential internal information. For that they widely employ on-chip memory encryption. Usually both data and address buses are encrypted to prevent microprobing attacks. This paper shows how practical such attacks can be on real chips and whether memory encryption is as good as it is supposed to be. It was possible to extract the whole memory from a secure 8-bit microcontroller with as little as 8 probing needles. This paper questions the usual belief in that ion-doping-encoded and encrypted Mask ROM is ultimately secure. Implications for 16-bit and 32-bit microcontrollers are discussed as well. Some common weaknesses are exposed and possible countermeasures are discussed.