International Association for Cryptologic Research

International Association
for Cryptologic Research


Zhe Liu


PLCrypto: A Symmetric Cryptographic Library for Programmable Logic Controllers 📺
Programmable Logic Controllers (PLCs) are control devices widely used in industrial automation. They can be found in critical infrastructures like power grids, water systems, nuclear plants, manufacturing systems, etc. This paper introduces PLCrypto, a software cryptographic library that implements lightweight symmetric cryptographic algorithms for PLCs using a standard PLC programming language called structured text (ST). To the best of our knowledge, PLCrypto is the first ST-based cryptographic library that is executable on commercial off-the-shelf PLCs. PLCrypto includes a wide range of commonly used algorithms, totaling ten algorithms, including one-way functions, message authentication codes, hash functions, block ciphers, and pseudo-random functions/generators. PLCrypto can be used to protect the confidentiality and integrity of data on PLCs without additional hardware or firmware modification. This paper also presents general optimization methodologies and techniques used in PLCrypto for implementing primitive operations like bit-shifting/rotation, substitution, and permutation. The optimization tricks we distilled from our practice can also guide future implementation of other computationheavy programs on PLCs. To demonstrate a use case of PLCrypto in practice, we further realize a cryptographic protocol called proof of aliveness as a case study. We benchmarked the algorithms and protocols in PLCrypto on a commercial PLC, Allen Bradley ControlLogix 5571, which is widely used in the real world. Also, we make our source codes publicly available, so plant operators can freely deploy our library in practice.
Persistent Fault Attack in Practice 📺
Persistence fault analysis (PFA) is a novel fault analysis technique proposed in CHES 2018 and demonstrated with rowhammer-based fault injections. However, whether such analysis can be applied to traditional fault attack scenario, together with its difficulty in practice, has not been carefully investigated. For the first time, a persistent fault attack is conducted on an unprotected AES implemented on ATmega163L microcontroller in this paper. Several critical challenges are solved with our new improvements, including (1) how to decide whether the fault is injected in SBox; (2) how to use the maximum likelihood estimation to pursue the minimum number of ciphertexts; (3) how to utilize the unknown fault in SBox to extract the key. Our experiments show that: to break AES with physical laser injections despite all these challenges, the minimum and average number of required ciphertexts are 926 and 1641, respectively. It is about 38% and 28% reductions of the ciphertexts required in comparison to 1493 and 2273 in previous work where both fault value and location have to be known. Furthermore, our analysis is extended to the PRESENT cipher. By applying the persistent fault analysis to the penultimate round, the full PRESENT key of 80 bits can be recovered. Eventually, an experimental validation is performed to confirm the accuracy of our attack with more insights. This paper solves the challenges in most aspects of practice and also demonstrates the feasibility and universality of PFA on SPN block ciphers.
SIDH on ARM: Faster Modular Multiplications for Faster Post-Quantum Supersingular Isogeny Key Exchange
We present high-speed implementations of the post-quantum supersingular isogeny Diffie-Hellman key exchange (SIDH) and the supersingular isogeny key encapsulation (SIKE) protocols for 32-bit ARMv7-A processors with NEON support. The high performance of our implementations is mainly due to carefully optimized multiprecision and modular arithmetic that finely integrates both ARM and NEON instructions in order to reduce the number of pipeline stalls and memory accesses, and a new Montgomery reduction technique that combines the use of the UMAAL instruction with a variant of the hybrid-scanning approach. In addition, we present efficient implementations of SIDH and SIKE for 64-bit ARMv8-A processors, based on a high-speed Montgomery multiplication that leverages the power of 64-bit instructions. Our experimental results consolidate the practicality of supersingular isogeny-based protocols for many real-world applications. For example, a full key-exchange execution of SIDHp503 is performed in about 176 million cycles on an ARM Cortex-A15 from the ARMv7-A family (i.e., 88 milliseconds @2.0GHz). On an ARM Cortex-A72 from the ARMv8-A family, the same operation can be carried out in about 90 million cycles (i.e., 45 milliseconds @1.992GHz). All our software is protected against timing and cache attacks. The techniques for modular multiplication presented in this work have broad applications to other cryptographic schemes.
Four$\mathbb {Q}$ on Embedded Devices with Strong Countermeasures Against Side-Channel Attacks
This work deals with the energy-efficient, high-speed and high-security implementation of elliptic curve scalar multiplication and elliptic curve Diffie-Hellman (ECDH) key exchange on embedded devices using Four$$\mathbb {Q}$$ and incorporating strong countermeasures to thwart a wide variety of side-channel attacks. First, we set new speed records for constant-time curve-based scalar multiplication and DH key exchange at the 128-bit security level with implementations targeting 8, 16 and 32-bit microcontrollers. For example, our software computes a static ECDH shared secret in $$\sim $$6.9 million cycles (or 0.86 s @8 MHz) on a low-power 8-bit AVR microcontroller which, compared to the fastest Curve25519 and genus-2 Kummer implementations on the same platform, offers 2$$\times $$ and 1.4$$\times $$ speedups, respectively. Similarly, it computes the same operation in $$\sim $$496 thousand cycles on a 32-bit ARM Cortex-M4 microcontroller, achieving a factor-2.9 speedup when compared to the fastest Curve25519 implementation targeting the same platform. Second, we engineer a set of side-channel countermeasures taking advantage of Four$$\mathbb {Q}$$’s rich arithmetic and propose a secure implementation that offers protection against a wide range of sophisticated side-channel attacks. Finally, we perform a differential power analysis evaluation of our software running on an ARM Cortex-M4, and report that no leakage was detected with up to 10 million traces. These results demonstrate the potential of deploying Four$$\mathbb {Q}$$ on low-power applications such as protocols for IoT.