The fast development of information technology and communication includes blockchain technology, artificial intelligence, and cloud computing. Medical cyber systems increasingly need secure data protection. Cloud computing provides the solution to the complexity of data but fails to provide secure data transmission. In blockchain technology, the decentralization specification provides secure authentication and secure data transmission. In this paper, we have reviewed Cheng et al. scheme which is published in the Journal of Medical Systems <https://doi.org/10.1007/s10916-019-1468-1>. In Cheng et al. scheme, we found security weaknesses and some possible security attacks such as clock synchronization attack, DoS attack, impersonation attack, fails to protect the session keys, and stolen verifier attack. Thus, Cheng et al. scheme is not satisfactory for medical secure data sharing for medical communication systems. At last, we suggest some improvements for Cheng et al. protocol.