Detection of probing attempts in secure ICs

Abstract

Physical attacks focus on extracting information from internal parts of IC's. One way to achieve this is by means of connecting probes to wires, so that the content of internal buses and registers can be revealed. Protection against this type of attacks exists, but usually is bulky and expensive, e.g. the shielding of secured areas. This paper presents a novel in-circuit countermeasure that is cheap and can easily be integrated in existing designs to detect probing attempts. It is based on a ring oscillator that operates over coupled lines in a differential mode. When the loading of one of the lines is unbalanced over a tolerance margin, an impulse is generated and integrated over time. If the integration surpasses a given threshold an alarm signal is activated. Simulations show the stability of the detector over a range of temperature and supply voltage variations

The Low Area Probing Detector as a Countermeasure Against Invasive Attacks

“…The circuit only consists of a few gates and has a significantly lower area than other protection mechanisms, such as the PAD [7] or bus encryption.…”

“…That way, probing can be detected no matter whether extensive FIB editing was used to uncover target lines, or whether a probe was connected on the back side. The only approach that detects such attacks and that has been evaluated with respect to process, voltage, and temperature variation is the probe attempt detector (PAD) by Manich et al [7] whose principle of operation is briefly described in Section II-B. However, the necessity of a large tank capacitor that needs to be charged and discharged still comes with an area, power, and timing overhead that prevents it from being used in ultralow resource applications.…”

“…A quantitative area, timing, and energy consumption comparison between the cryptographically secure shields by Cioranesco et al [11], the PAD [7], and the LAPD is shown in Table VII. All three implementations are available in the same STMicroelectronics 65-nm technology (the PAD implementation in this technology is currently not published).…”

“…The PAD was proposed in [7] and is the first technique detecting physical attacks in buses by measuring the modification of parasitics provoked in the lines.…”

“…In the following years, industry and academia have been working on countermeasures against microprobing. Masking schemes were implemented to make probing single lines worthless [6]; circuits dedicated to the detection of microprobes based on their parasitic capacitance have been proposed [7], [8] and also other circuits proposed in academia that can detect microprobes as a side effect [9].…”