A new paper on the arXiv makes headway toward showing that quantum-computation, classical-communication (QCCC) key agreement cannot be achieved securely. The authors present what they describe as the first unconditional polynomial-query attacks that tolerate imperfect completeness, a condition where the protocol occasionally fails even when both parties are honest.
The attacks operate in the quantum random oracle model (QROM), a standard setting for analyzing quantum cryptographic schemes. By allowing for imperfect completeness, the result strengthens previous impossibility-style arguments, which often assume perfect reliability. The work does not yet prove full impossibility, but it narrows the gap.
Because the abstract is truncated, the exact technical scope of the attacks is not fully detailed here. The paper's contribution is a step toward establishing fundamental limits on what QCCC key agreement can achieve.