Post-Quantum Security of Block Cipher Constructions

2025-10-09

AI Summary

The theoretical foundations for the security of block ciphers in quantum computing environments remain underdeveloped. Method: This paper establishes, for the first time, a systematic theoretical framework for post-quantum secure block ciphers. Working within both the standard model and the quantum ideal cipher model, it employs quantum query models and security reduction techniques—integrating quantum random oracles and ideal cipher primitives—to analyze key constructions (e.g., FX, LRW, XEX) and mainstream authenticated encryption modes. Contribution/Results: It delivers the first rigorous post-quantum security proofs for these schemes, thereby filling a critical gap in the formal analysis of symmetric-key cryptography under quantum adversaries. The results provide verifiable security guarantees for FX-based key expansion, tweakable block ciphers, and practical authenticated encryption schemes. By unifying quantum-security modeling and reductionist proof methodology, this work substantively advances the post-quantum migration of symmetric cryptography.

Technology Category

• Machine Learning: Quantum Machine Learning
• Reasoning under Uncertainty: Other Foundations of Reasoning under Uncertainty
• Computer Vision: Other Foundations of Computer Vision

Application Category

• Security and Privacy: Applications of cryptography
• Economics, Online Markets and Human Computation: Economic aspects of blockchain and cryptocurrencies
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

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.

Problem

• Analyzing post-quantum security of symmetric-key block ciphers
• Providing quantum security proofs for encryption modes
• Establishing foundations for post-quantum block cipher theory

Innovation

• Developed post-quantum security proofs for block ciphers
• Applied techniques to FX, LRW, XEX constructions
• Used quantum ideal cipher model for security analysis