In drone environments using batteries, it is important to reduce unnecessary overhead. Also, for security of data, encryption is also an important factor. However, in the case of encryption, overhead is generated, but encryption and overhead are always in a trade-off relationship in this way. In this paper, in order to reduce overhead of drone, the concept of reliability was applied. We applied low level security to drone with high reliability to reduce overhead and conversely applied high level security to drone with low reliability. In order to adjust the security level, adjust the size of Key used for encryption and reduce the weight of the security algorithm itself. The reliability of the drone was determined based on the number of times of receiving data and by applying group reliability through drone grouping, it was made possible to determine hierarchical reliability. Moreover, by storing the communication records of all drones in the blockchain, the integrity of the reliability is guaranteed.