Comment on "A novel quantum deniable authentication protocol without entanglement"

Shi et al. (Quantum Inf Process 14(6):2183–2193, 2015) proposed a novel quantum deniable authentication protocol in which new shared secret keys can be updated timely with the help of a trusted party, and the fact that only the specified receiver could identify the true source of a given message is guaranteed by the new shared secret keys generated in the key update phase. Hence, the core of Shi et al.'s protocol is the key update phase . However, the analysis in this paper shows that there is a bug in the key update phase, which can lead to the failure of updating the shared key. Furthermore, an improved simple method is proposed to mitigate the security weakness.