Literature Study: Blockchain-Based Reversible Data Hiding for Securing Medical Images
Published Journal: Journal of Healthcare Engineering
Blockchain Technology - Study Notes
Blockchain is a distributed ledger system that was developed to work in an environment where the parties involved do not trust each other. In contrast to traditional server-centric models, blockchain requires each participating node to store a copy of the ledger that records all transaction details. Since the ledger is held locally by all participating nodes, they can perform audits of transactions locally. With this feature, even if there is no trust between participating nodes, one can still trust the consensus achieved through the blockchain.
Another unique feature offered by blockchain is the introduction of cryptographic hashes to link all transaction records. Referring to the diagram below, all valid transactions are grouped into a block at a fixed time interval. A new hash is generated based on these transaction details and the hash of the previous block. Next comes a consensus process (e.g., Proof of Work (PoW)) to approve transactions. During the consensus process, only nodes that successfully solve a given puzzle can add that block to the existing blockchain. The hash generation of each transaction block is linked to the hash of the previous block. To modify a transaction record in the blockchain, a large number of valid blocks must be generated through the consensus process, and subsequent blocks must be overwritten. Since PoW is a time-consuming process, it is difficult to generate large numbers of new blocks in a short period of time; this makes blockchain an immutable solution for many applications.
Reaching consensus through the PoW process in the blockchain is time-consuming, which makes transactions slow (e.g. 10 minutes for Bitcoin). Another option is to adopt a consortium blockchain, where a list of trusted members is predefined. In this case, a lightweight consensus process such as Practical Byzantine Fault Tolerance (PBZT) can be used. This allows for more timely communication between nodes in the same consortium blockchain without sacrificing key security features in the blockchain (i.e. auditability, traceability and integrity).
Blockchain Technology Application in RDH-EI
Doctor A first encrypts the patient's medical records, and then uses the proposed RDHEI scheme to generate a secret-encrypted image (CSMI), where the encrypted medical records are embedded into the patient's medical images. His encrypted medical records and CSMI are stored in the database of his hospital (Hospital X), a block of transactions is generated and added to the blockchain. Through the proposed blockchain system, anyone who wants to share medical information can verify the integrity of the transmitted data at the receiving end. For example, doctor A shares CSMI with doctor B and medical institute Y. After receiving the CSMI, doctor B first calculates the hash value of the received data and compares it with the blockchain to verify its integrity. He then used the legitimate key to extract the hidden medical records, and then used another legitimate key to decrypt the medical records. A similar procedure was carried out at the Institute of Medicine Y.