Paper 2025/2309 Original: eprint.iacr.org/2025/2309 ↗

On the Concrete Practicality of Post-Quantum Multi-Authority Attribute-Based Encryption

Abstract

The transition of cryptographic primitives to the post-quantum era necessitates the rigorous translation of asymptotic security proofs into concrete parameter instantiations. This paper evaluates the practical realizability of the Decentralized Multi-Authority Attribute-Based Encryption (MA-ABE) scheme by Datta, Komargodski, and Waters (Eurocrypt 2021), a seminal construction relying exclusively on the Learning With Errors (LWE) assumption. While DKW21 eliminates the reliance on bilinear maps, offering resilience against quantum adversaries, our comprehensive numerical audit reveals a profound dichotomy between its theoretical soundness and practical feasibility. We demonstrate that the convergence of constraints derived from LWE hardness and the noise flooding technique required for simulation-based security forces the modulus-to-noise ratio into a super-polynomial regime. Consequently, the requisite parameters---particularly the smudging bound $\hat{B}$---scale astronomically ($\approx 10^{47}$), rendering the scheme unimplementable on existing computational substrates. Beyond identifying this "Parameter Wall," this work proposes a radical architectural reconfiguration to bridge the gap between theory and practice. We introduce novel optimization strategies including the transition to non-commutative Module-LWE structures, the invention of Coset-Restricted Lattice Hashing to minimize pre-image norms, and the adoption of Entropic Smudging via Lossy Trapdoors. Furthermore, we explore Isospectral Lattice Deformations and Learning With Rounding (LWR) transformations to decouple security constraints from decryption correctness, outlining a viable roadmap for practical post-quantum access control.