Hardware Trojans and Other Threats against Embedded Systems

Abstract

Countless systems ranging from consumer electronics to military equipment are dependent on integrated circuits (ICs). A surprisingly large number of such systems are already security- critical, e.g., automotive electronics, medical devices, or SCADA systems. If the underlying ICs in such applications are maliciously manipulated through hardware Trojans, the security of the entire system can be compromised. In recent years, hardware Trojans have drawn the attention of the scientific community and government. Initially, the primary attacker model was a malicious foundry that could alter the design, i.e., introduce hardware Trojans which could interfere with the functionality of a chip. Many other attacker models exist too. For instance, a legitimate IC manufacturer, such as a consumer electronics company, might be in cohort with a national intelligence agency and could alter its products in a way that compromises their security. Even though hardware Trojans have been studied for a decade or so in the literature, little is known about how they might look, and what the "use cases" for them is. We describe two applications for low-level hardware manipulations. One introduces an ASIC Trojans by sub-transistor changes, and the other is a novel type of fault-injection attacks against FPGAs. As an example for an extremely stealthy manipulations, we show how a dangerous Trojans can be introduced by merely changing the dopant polarity of selected existing transistors of a design. The Trojan manipulates the digital post-processing of Intel's cryptographically secure random number generator used in the Ivy Bridge processors. The adversary is capable of exactly controlling the entropy of the RNG. For example, the attacker can reduce the RNG's entropy to 40 bits of randomness. Due to the AES-based one-way function after the entropy extracting, the Trojan is very difficult to detect. Crucially, this approach does not require to add new circuits to the IC. Since the modified circuit appears legitimate on all wiring layers (including all metal and polysilicon), our family of Trojans is resistant to many detection techniques, including fine-grain optical inspection and checking against "golden chips". As a second "use case", we show how an adversary can extract cryptographic keys from an unknown FPGA design. The attack, coined bitstream fault injection (BiFI), systematically manipulates the bitstream by changing random LUT contents, configures the target device, and collects the resulting faulty ciphertexts. The ciphertexts are used to recover the key by testing a set of hypotheses, e.g., that the ciphertext is the plaintext XORed with the key. The attack only needs a black-box assumption about the bitstream structure and format. It was verified by considering a set of 3 rd party AES designs on different standard FPGAs. In 15 out of 16 designs, we were able to extract the AES key.