 The major difference of quantum key distribution is the ability to detect any interception of the key, whereas with courier the key security cannot be proven or tested.QKD (Quantum Key Distribution) systems also have the advantage of being automatic, with greater reliability and lower operating costs than a secure human courier network.Kak's three-stage protocol has been proposed as a method for secure communication that is entirely quantum unlike quantum key distribution in which the cryptographic transformation uses classical algorithms

Factors preventing wide adoption of quantum key distribution outside high security areas include the cost of equipment, and the lack of a demonstrated threat to existing key exchange protocols.