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In the Quantum Key Distribution protocol BB84, Alice sends x qubits to Bob. There is no acknowledgement of receipt. This cannot be done over the quantum channel. If I need an acknowledgement, it must be sent via a classical channel. But that means that I am sending two messages independently of each other, which brings us to the two generals problem. Do I understand this correctly? Or am I missing something that could help me confirm the transmission similarly to TCP?

Duckling
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From Laudenbach paper Continuous-Variable Quantum Key Distribution with Gaussian Modulation - The Theory of Practical Implementations:

Quantum key distribution is a method to generate a secret key between two distant parties, Alice and Bob, based on transmitting non-orthogonal quantum states. After the transmission and measurement of these quantum states, Alice and Bob exchange classical messages and perform post-processing to generate a secure key. In order to prevent a man-in-the-middle attack, Alice and Bob need to authenticate these classical messages in advance (so strictly speaking QKD is a key-growing protocol).

So BB84 works only if you have an authenticate classical channel. I guess this assumption ends the Two Generals' Problem. Am I right?

Troncho Col
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