Abstract: In medical blockchain systems, users may be cheated by whole node when they request data from the whole node. Meanwhile, owing to the lack of storage, simple payment verification (SPV) and other verification methods of light node data are not applicable to medical blockchain systems. In order to solve these problems, this paper proposes a new light node data query method for medical blockchains. In the proposed method, the Merkle mountain range (MMR) with dynamic addition capability is introduced, and the latest valid block query algorithm based on recommendation trusted node selection and trusted node verification on sampling is designed. Accordingly, by using the commitment mechanism of the MMR and Merkle tree, the medical data sent by the whole node are verified by the user of the light node which holds the latest valid block obtained from a trusted node. Furthermore, the proposed method can be extended to the application of consortium blockchains. Analysis and experiments on the proposed method show that both time cost and space cost are in low overhead ranges.

Key words: light node, Merkle mountain range (MMR), data query, medical blockchain