International Association for Cryptologic Research

International Association
for Cryptologic Research


Nele Mentens

Affiliation: KU Leuven


Security on Plastics: Fake or Real? 📺
Electronic devices on plastic foil, also referred to as flexible electronics, are making their way into mainstream applications. In the near future, flexible electronic labels can be embedded in smart blisters, but also used as mainstream technology for flexible medical patches. A key technology for flexible electronics is based on thin-film transistors, which have the potential to be manufactured at low cost, making them an ideal candidate for these applications. Yet, up to now, no-one is taking digital security into account in the design of flexible electronics.In this paper, we present, to our knowledge, the first cryptographic core on plastic foil. Two main research challenges arise. The first challenge is related to the reliability of the circuit, which typically decreases when the circuit area increases. By integrating cryptographic modules, we explore the limits of the technology, since the smallest lightweight block ciphers feature a larger area than the largest digital circuit on flex foil reported up to now. The second challenge is related to key hiding. The relatively large features on the chip and the fact that electronic chips on plastics are used as bare dies, i.e. they are not packaged, make it easy to read out the value of the stored secret key. Because there is no dedicated non-volatile memory technology yet, existing methods for writing data to the flexible chip after fabrication are based on wire cutting with a laser or inkjet printing. With these techniques, however, it is extremely easy to “see” the value of the secret key under a microscope. We propose a novel solution that allows us to invisibly program the key after fabrication.
ES-TRNG: A High-throughput, Low-area True Random Number Generator based on Edge Sampling
In this paper we present a novel true random number generator based on high-precision edge sampling. We use two novel techniques to increase the throughput and reduce the area of the proposed randomness source: variable-precision phase encoding and repetitive sampling. The first technique consists of encoding the oscillator phase with high precision in the regions around the signal edges and with low precision everywhere else. This technique results in a compact implementation at the expense of reduced entropy in some samples. The second technique consists of repeating the sampling at high frequency until the phase region encoded with high precision is captured. This technique ensures that only the high-entropy bits are sent to the output. The combination of the two proposed techniques results in a secure TRNG, which suits both ASIC and FPGA implementations. The core part of the proposed generator is implemented with 10 look-up tables (LUTs) and 5 flip-flops (FFs) of a Xilinx Spartan-6 FPGA, and achieves a throughput of 1.15 Mbps with 0.997 bits of Shannon entropy. On Intel Cyclone V FPGAs, this implementation uses 10 LUTs and 6 FFs, and achieves a throughput of 1.07 Mbps. This TRNG design is supported by a stochastic model and a formal security evaluation.
An Elliptic Curve Processor Suitable For RFID-Tags
RFID-Tags are small devices used for identification purposes in many applications nowadays. It is expected that they will enable many new applications and link the physical and the virtual world in the near future. Since the processing power of these devices is low, they are often in the line of fire when their security and privacy is concerned. It is widely believed that devices with such constrained resources can not carry out sufficient cryptographic operations to guarantee security in new applications. In this paper, we show that identification of RFID-Tags can reach high security levels. In particular, we show how secure identification protocols based on the DL problem on elliptic curves are implemented on a constrained device such as an RFID-Tag requiring between 8500 and 14000 gates, depending on the implementation characteristics. We investigate the case of elliptic curves over $F_{2^p}$ with p prime and over composite fields $F_{2^{2p}}$. The implementations in this paper make RFID-Tags suitable for anti-counterfeiting purposes even in the off-line setting.

Program Committees

CHES 2019