Quantum key distribution (QKD) is a secure communication method that enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages. Quantum key distribution is only used to produce and distribute a key, not to transmit any message data. The algorithm most commonly associated with QKD is the one-time pad, as it is provably secure when used with a secret, random key. QKD is more of a communication architecture than a cryptographic protocol.
Quantum Key Exchange (QKE) on the other hand is a cryptographic concept originally explored by Donald Beaver. There is a seminal paper of the deniability of QKE published in 2002 itself. There are a few variants of QKE like authenticated QKE, Entanglement Distillation QKE etc. Please refer to this recent paper on QKE with reference to the aspects of covert communication and entanglement distillation.
There are some clear distinctions between QKD and QKE such as the following.
- QKD usually relies on having an authenticated classical channel of communications whereas QKE is a collection of cryptographic properties of Quantum Information with a focus on the Quantum Computational Complexity theory
- QKD uses classical encryption schemes such as one-time-pads whereas QKE does not employ any classical cryptographic devices and schemes.