| Contributors: |
Lund University, Faculty of Engineering, LTH, Departments at LTH, Department of Electrical and Information Technology, Secure and Networked Systems, Lunds universitet, Lunds Tekniska Högskola, Institutioner vid LTH, Institutionen för elektro- och informationsteknik, Säkerhets- och nätverkssystem, Originator, Lund University, Faculty of Engineering, LTH, LTH Profile areas, LTH Profile Area: AI and Digitalization, Lunds universitet, Lunds Tekniska Högskola, LTH profilområden, LTH profilområde: AI och digitalisering, Originator, Lund University, Profile areas and other strong research environments, Strategic research areas (SRA), ELLIIT: the Linköping-Lund initiative on IT and mobile communication, Lunds universitet, Profilområden och andra starka forskningsmiljöer, Strategiska forskningsområden (SFO), ELLIIT: the Linköping-Lund initiative on IT and mobile communication, Originator |
| Description: |
The Hamming Quasi-Cyclic (HQC) key encapsulation mechanism (KEM), recently selected by NIST for standardization in the Post-Quantum Cryptography (PQC) process, distinguishes itself through its efficiency, robust design based on hard decoding problems in coding theory, and well-characterized decryption failure rates. Despite its selection, practical security concerns arise from implementation threats, particularly those exploiting plaintext-checking (PC) oracles. While multi-value PC (MV-PC) and full decryption (FD) oracle attacks have been extensively studied in the context of lattice-based cryptography, their applicability to code-based schemes like HQC has remained relatively unexplored. In this work, we present the first MV-PC and FD oracle attacks targeting code-based KEMs, specifically on HQC. Our MV-PC attack significantly reduces the required oracle queries compared to previous PC oracle-based methods and holds implications for side-channel, key-mismatch, and fault-injection attacks. Our FD attack exhibits remarkable efficiency in trace complexity, achieving secret key recovery for hqc-128 with just two queries to a perfect oracle, and four queries for hqc-192 and hqc-256. Simulations further demonstrate the robustness of our MV-PC and FD oracle attacks against imperfect oracle responses. We experimentally validate the new attacks on an ARM Cortex-M4 microcontroller, highlighting the critical need for robust countermeasures. In particular, on such a platform, substantial leakage during operations like syndrome computation poses significant challenges to the efficiency of masking techniques in mitigating FD oracle attacks. |
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