A note on "new quantum key agreement protocols based on Bell states"

We remark that the quantum key agreement protocol (Yang et al. in Quantum Inf Process 18(10):322, 2019) is flawed. It is unnecessary for Bob to prepare his secret key K-B, because it is finally announced and accessible to adversaries. We find, K-B has no relation to the confidentiality of the final agreed key K-AB = K-A circle plus K-B. It is just a key transfer scheme, not a general key agreement scheme. We also find there is short of a code for Bob to extract bits from the measured results.