Paper 2026/209

Post-Quantum Security of Block Cipher Constructions

Chen Bai, Virginia Tech

Christian Majenz, Technical University of Denmark

Kaiyan Shi, University of Maryland, College Park

Abstract

Block ciphers are versatile cryptographic ingredients that are used in a wide range of applications ranging from secure Internet communications to disk encryption. While post-quantum security of public-key cryptography has received significant attention, the case of symmetric-key cryptography (and block ciphers in particular) remains a largely unexplored topic. In this work, we set the foundations for a theory of post-quantum security for block ciphers and associated constructions. Leveraging our new techniques, we provide the first post-quantum security proofs for the key-length extension scheme FX, the tweakable block ciphers LRW and XEX, and most block cipher encryption and authentication modes. Our techniques can be used for security proofs in both the plain model and the quantum ideal cipher model. Our work takes significant initial steps in establishing a rigorous understanding of the post-quantum security of practical symmetric-key cryptography.

@misc{cryptoeprint:2026/209,
      author = {Gorjan Alagic and Chen Bai and Christian Majenz and Kaiyan Shi},
      title = {Post-Quantum Security of Block Cipher Constructions},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/209},
      year = {2026},
      url = {https://eprint.iacr.org/2026/209}
}