Built-in Software Obfuscation for Protecting Microprocessors against Hardware Trojan Horses

Hardware Trojan Horses (HTHs) are today a serious issue for both academy and industry because of their dramatic complexity and dangerousness. Indeed, it has been shown that HTHs may be effectively inserted in modern microprocessors allowing the attacker to run malicious software, to acquire root privileges and to steal secret information. We aim at reducing the dangerousness of information stealing HTHs by introducing a hardware security module in the microprocessor under protection. In particular, the proposed module is in charge of interacting with the execution flow in order to introduce software obfuscation during programs execution at runtime. The goal of such obfuscation is to minimize the probability of exposing sensitive information to the HTH by encrypting/decrypting it, by spreading it through microprocessor's registers and by submerging it among garbage data. We implemented a prototype of the proposed hardware security module and we proved its effectiveness and efficiency (in terms of area occupation and working frequency reduction) by integrating it into the RSD 32bit speculative, superscalar and out-of-order RISC-V microprocessor running a set of benchmark programs¹,.