Preprint shows single-hash QKD post-processing preserves key rate under modified secrecy definition

The paper proves that security of the combined protocol follows directly from a slightly relaxed secrecy guarantee on the version without the final error-verification bits. This removes the need for two separate universal hash families, cuts classical communication, and lowers the randomness requirement. The argument applies to most existing entropy-based security proofs without altering the asymptotic key rate.

Standard QKD stacks treat error verification and privacy amplification as sequential, independent steps that each consume fresh randomness and communication. The new construction re-uses the same hash output for both tasks, announcing only a fixed number of bits for verification. The authors show the statistical distance to the ideal key increases by at most the verification failure probability, which can be made exponentially small.

Commercial QKD systems already face tight constraints on classical post-processing latency and hardware random-number generation. Integrating the two steps therefore offers a concrete engineering simplification that does not trade off the finite-key rate derived from smooth min-entropy bounds. The result directly supports the editorial priority of lowering barriers to scalable quantum networks.

The work remains a theoretical security reduction; experimental validation on deployed fiber or satellite links is still required to quantify any side-channel leakage introduced by the joint hash implementation.