Daniel J. Bernstein
University of Illinois at Chicago, Chicago, IL 60607-7045, USA; Academia Sinica, Taipei, Taiwan

Karthikeyan Bhargavan
Inria, Paris, France; Cryspen, Berlin, Germany

Shivam Bhasin
National Integrated Centre for Evaluation, Nanyang Technological University, Singapore; Temasek Labs, Nanyang Technological University, Singapore

Anupam Chattopadhyay
College of Computing and Data Science, Nanyang Technological University, Singapore; Temasek Labs, Nanyang Technological University, Singapore

Tee Kiah Chia
Temasek Labs, Nanyang Technological University, Singapore

Matthias J. Kannwischer
Quantum Safe Migration Center, Chelpis Quantum Tech, Taipei, Taiwan

Franziskus Kiefer
Cryspen, Berlin, Germany

Thales B. Paiva
University of Sao Paulo, Sao Paulo, Brazil; Fundep, Belo Horizonte, Brazil; CASNAV, Rio de Janeiro, Brazil

Prasanna Ravi
College of Computing and Data Science, Nanyang Technological University, Singapore; Temasek Labs, Nanyang Technological University, Singapore

Goutam Tamvada
Cryspen, Berlin, Germany

Keywords: KyberSlash, PQC, Kyber, ML-KEM, Timing attacks, Division timing

Abstract

This paper presents KyberSlash1 and KyberSlash2 – two timing vulnerabilities in several implementations (including the official reference code) of the Kyber Post-Quantum Key Encapsulation Mechanism, recently standardized as ML-KEM. We demonstrate the exploitability of both KyberSlash1 and KyberSlash2 on two popular platforms: the Raspberry Pi 2 (Arm Cortex-A7) and the Arm Cortex-M4 microprocessor. Kyber secret keys are reliably recovered within minutes for KyberSlash2 and a few hours for KyberSlash1. We responsibly disclosed these vulnerabilities to maintainers of various libraries and they have swiftly been patched. We present two approaches for detecting and avoiding similar vulnerabilities. First, we patch the dynamic analysis tool Valgrind to allow detection of variable-time instructions operating on secret data, and apply it to more than 1000 implementations of cryptographic primitives in SUPERCOP. We report multiple findings. Second, we propose a more rigid approach to guarantee the absence of variable-time instructions in cryptographic software using formal methods.