I am in the Digital Security Group at Radboud University Nijmegen since September 2021, under the supervision of Bart Mennink and with Joan Daemen as promotor. During my PhD, I had the opportunity to complete a 6-month internship at CSEM, under the supervision of Damian Vizár. Before that, I completed my Master’s thesis at the University of Grenoble under the supervision of Pierre Karpman. Most of my current research focuses on the provable security of symmetric cryptographic schemes, particularly permutation-based ones. In general, I am interested in all aspects of cryptology.

Works

• Permutation-Based Hashing with Stronger (Second) Preimage Resistance
  Siwei Sun, Shun Li, Zhiyu Zhang, Charlotte Lefevre, Bart Mennink, Zhen Qin, Dengguo Feng
  
• MacaKey: Full-State Keyed Sponge Meets the Summation-Truncation Hybrid
  Charlotte Lefevre, Mario Marhuenda Beltrán
  
• SoK: Security of the Ascon Modes
  Charlotte Lefevre, Bart Mennink
  IACR Transactions on Symmetric Cryptology, 2025(1), pp. 138-210 (2025)
  
• To Pad or Not to Pad? Padding-Free Arithmetization-Oriented Sponges
  Mario Marhuenda Beltrán, Charlotte Lefevre, Bart Mennink
  IACR Transactions on Symmetric Cryptology, 2025(1), pp. 97-137 (2025)
  
• Permutation-Based Hash Chains with Application to Password Hashing
  Charlotte Lefevre, Bart Mennink
  IACR Transactions on Symmetric Cryptology 2024(4), pp. 249-286 (2024)
  best paper award
  
• Generic Security of the Ascon Mode: On the Power of Key Blinding
  Charlotte Lefevre, Bart Mennink
  Selected Areas in Cryptography, SAC 2024, pp. 3-32
  
• Kirby: A Robust Permutation-Based PRF Construction
  Charlotte Lefevre, Yanis Belkheyar, Joan Daemen
  
• Permutation-Based Hashing Beyond the Birthday Bound
  Charlotte Lefevre, Bart Mennink
  IACR Transactions on Symmetric Cryptology 2024(1), pp. 71-113 (2024)
  
• A Note on Adversarial Online Complexity in Security Proofs of Duplex-Based Authenticated Encryption Modes
  Charlotte Lefevre
  
• Indifferentiability of the Sponge Construction with a Restricted Number of Message Blocks
  Charlotte Lefevre
  IACR Transactions on Symmetric Cryptology 2023(1), pp. 224-243 (2023)
  
• Tight Preimage Resistance of the Sponge Construction
  Charlotte Lefevre, Bart Mennink
  CRYPTO 2022 (IV). LNCS, vol. 13510, pp. 185-204. Springer (2022)
  
• Time-memory tradeoffs for large-weight syndrome decoding in ternary codes
  Pierre Karpman, Charlotte Lefevre
  PKC 2022. LNCS, vol. 13177. pp. 82-111. Springer (2022)
  

Activites

Teaching

Teaching assistant in Radboud University for the following bachelor courses:

• 2024-2025 Mathematical Structures (NWI-IPC020)
• 2023-2024 Logics and Applications (NWI-IPI004)
• 2022-2023 Logics and Applications (NWI-IPI004)
• 2021-2022 Logics and Applications (NWI-IPI004)

Editorial

Program Committee:

• FSE 2027/ToSC 2026/2027
• SAC 2026
• ProTeCS 2026
• Inscrypt 2025

External reviewer:

• EUROCRYPT 2026
• CRYPTO 2025, 2024, 2023
• ASIACRYPT 2025, 2023, 2022
• Journal of Cryptology (2024)
• Inscrypt 2024
• Designs, Codes, and Cryptography (2023)

Organization

• Part of the organizing team of Online GAPS seminar
• Co-organizer of GelreCrypt 2025 (Nijmegen, November 2025)

Selected Presentations

CV

PhD

Provable Security of Permutation-Based Cryptography

Members of the Doctoral Examination Board

• prof. dr. J.J.C. Daemen (supervisor)
• prof. dr. B.J.M. Mennink (co-supervisor)
• prof. dr. J.H. Geuvers (manuscript committee)
• prof. dr. T. Ristenpart (manuscript committee)
• dr. M. Eichlseder (manuscript committee)
• dr. G. Leurent (manuscript committee)
• dr. M. Stam
• dr. M.T.C. Venema
• prof. dr. L. Batina (acting rector)

Date, Time, and Location

Tuesday, 10th February at 12h30

Comeniuslaan 2, 6525HP Nijmegen

Abstract

Permutation-based cryptography, in particular the sponge construction, has become central to the design of lightweight symmetric schemes. In this thesis, we advance the state of provable security for permutation- based designs in several ways.

First, we establish tight bounds on the preimage resistance of the sponge construction using a new proof technique. This result significantly improves generic preimage security for many lightweight schemes. In addition, we prove indifferentiability of the sponge in two scenarios that have received limited attention: (i) when input messages are bounded in size, and (ii) when inputs are not required to remain secret.

Second, we introduce new sponge-based constructions. We propose the double sponge, the first permutation-based hash function to achieve indifferentiability security beyond the birthday bound in the capacity. We also present two efficient sponge-based pseudorandom function con- structions which outperform existing state-of-the-art designs in terms of efficiency.

Next, we explore permutation-based hashing in specific contexts, namely password-based hash chains and finite-field-oriented designs. Our results demonstrate that dedicated analysis and small design tweaks can yield stronger security guarantees and more efficient schemes.

Finally, we unify and sharpen the generic security analysis of the authenticated encryption mode of Ascon, the winner of the Lightweight Cryptography competition organized by the US National Institute of Standards and Technology. We systematize existing knowledge, introduce a novel security model, and fill important gaps, which together complete the picture of its generic security.