Analysis of Counterfactual Quantum Certificate Authorization

A counterfactual quantum certificate authorization protocol was proposed recently (Shenoy et al., Phys. Rev. A 89 , 052307 ( 20 )), in which a trusted third party, Alice, authenticates an entity Bob (e.g., a bank) that a client Charlie wishes to securely transact with. However, this protocol requires a classical authenticated channel between Bob and Charlie to prevent possible attacks from the third party Alice, which is in conflict with the task of certificate authorization in the sense that Bob and Charlie can establish an unconditionally-secure key by a quantum key distribution protocol if there is a classical authenticated channel between them and hence securely transact with each other even without the assistance of the third party Alice.