  Quantum coherence was recently formalized as a physical resource to measure
the strength of superposition. Based on the resource theory, we present a
systematic framework that connects a coherence measure to the security of
quantum key distribution. By considering a generic entanglement-based key
distribution protocol under the collective attack scenario, we show that the
key rate can be quantified by the coherence of the shared bipartite states.
This framework allows us to derive the key rate of the BB84 and six-state
protocols. By utilizing fine-grained parameters, we also derive the improved
key rates of both protocols within the coherence-based framework. Furthermore,
we apply it to a practical issue, detection efficiency mismatch, and obtain an
improved result. In conclusion, this framework demonstrates the interplay among
coherence, entanglement, and quantum key distribution at a fundamental level.
