An Efficient Reconfigurable Ring Oscillator for Hardware Trojan Detection

The threat of inserting malicious logic in hardware design is increasing as the digital supply chains are becoming more deep and span the whole globe. Ring oscillators (ROs) can be used to detect deviations of circuit operations due to changes of its layout caused by the insertion of a hardware Trojan horse (Trojan). The placement and the length of the ring oscillator are two important parameters that define an RO sensitivity and capability to detect malicious alternations. We propose and study the use of ring oscillators with variable lengths, configurable at the runtime. Such oscillators push further the envelope for the attackers, as their design must be undetectable by all supported lengths. We study the efficiency of our proposal on defending against a family of hardware Trojans against an implementation of the AES cryptographic algorithm on an FPGA.