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Has MIMO decoding been proved hard from lattice problems?
Researchers show the published lattice-hardness proof for MIMO decoding fails, as Regev's LWE reduction structure does not carry over to non-modular MIMO.
The paper re-examines Dean and Goldsmith's proposed polynomial-time reduction from lattice problems to MIMO decoding, which adapted Regev's reduction for learning with errors (LWE). Prior works had presented attacks and counterexamples against the construction, leaving the reduction's precise validity unclear. The authors identify which structural features of the LWE reduction fail to transfer to the non-modular MIMO setting, showing the published proof does not establish the claimed hardness of MIMO decoding. They distinguish flaws in the hardness proof from direct attacks on specific parameter choices and do not rule out physical layer security for MIMO systems in general.
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EFI Pairs Without One-Way Puzzles: Oracle Separations from Communication Complexity
Theorists build a classical oracle where one-way puzzles fail yet EFI pairs survive, separating two candidate minimal assumptions of quantum cryptography.
The paper constructs a single classical oracle relative to which one-way puzzles do not exist, even with an unbounded verifier, while an EFI pair survives every classical-query distinguisher holding advice, making one superposition query at the end. Security is proven by reducing adversary knowledge to communication complexity for Vector-in-Subspace, with the superposition query bounded using random matrix theory. Relative to the oracle, quantum polynomial time offers no advantage on tasks with classical inputs and outputs and there is no proof of quantumness, separating the leading minimal assumptions of quantum cryptography.
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