Smart healthcare has become more and more popular as information technology has developed. In the contemporary information era, smart healthcare makes healthcare more efficient, convenient, and customized by completely changing the traditional medical system. Even if there are many ways that these advancements improve people's lives, one of the main concerns is still the security of the vast data transmission. In order to solve this issue, a novel approach on Crow search optimized DNA encryption for SEcure medical data Transmission (CD-SET), for secure data transmission through unsecure channel is introduced in this paper. The proposed CD-SET model enhances the data transmission security by employing robust cryptographic techniques while transmitting through an unsecure channel. Initially medical image input is given to the encryption algorithm which combines DNA encryption and homomorphic encryption. The data will be first encrypted using DNA sequencing based on the sequence of the four chemical bases such as A, C, G, and T that comprise DNA. The DNA sequencing is given as input for HE Encryption process in which the key generation is performed using crow search algorithm. Then, the cloud stores the encrypted data so that it can be accessed. Python simulator is used to evaluate the proposed technique. The efficiency has been evaluated using encryption, decryption and execution time with the existing technique. The recommended technique can be implemented in 3% less time with the Dynamic DNA encryption system and Cryptosystem using SHA-512 algorithm and 7% less time with the Robust S-Box building method algorithm.