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BPDS: A Blockchain based Privacy-Preserving Data Sharing for Electronic Medical Records
Jingwei Liu, Xiaolu Li, Lin Ye, Hongli Zhang, Xiaojiang Du, Mohsen Guizani
TL;DR
Fragmented EMRs create sharing barriers while exposing highly sensitive patient information to privacy and security risks. BPDS combines cloud storage, consortium blockchain, CP-ABE access control, CES, and smart contracts for controlled EMR sharing. The authors report that the design provides secure storage and sharing, tamper resistance, and strong privacy preservation.
Problem
Fragmented EMRs hinder healthcare data sharing, while their sensitivity makes privacy and security important concerns.
Method
BPDS stores original EMRs in the cloud, records indexes on a consortium blockchain, and combines CP-ABE, CES, and smart contracts for controlled sharing.
Results
BPDS provides tamper-proof EMR indexes, reduced risk of original-data leakage, secure data storing and sharing, and patient control over EMRs.
Takeaways & Limitations
BPDS offers a blockchain-based infrastructure in which users or institutions can use EMR data while preserving patients’ privacy.
Abstract
from arXiv · showhide
Electronic medical record (EMR) is a crucial form of healthcare data, currently drawing a lot of attention. Sharing health data is considered to be a critical approach to improve the quality of healthcare service and reduce medical costs. However, EMRs are fragmented across decentralized hospitals, which hinders data sharing and puts patients' privacy at risks. To address these issues, we propose a blockchain based privacy-preserving data sharing for EMRs, called BPDS. In BPDS, the original EMRs are stored securely in the cloud and the indexes are reserved in a tamper-proof consortium blockchain. By this means, the risk of the medical data leakage could be greatly reduced, and at the same time, the indexes in blockchain ensure that the EMRs can not be modified arbitrarily. Secure data sharing can be accomplished automatically according to the predefined access permissions of patients through the smart contracts of blockchain. Besides, the joint-design of the CP-ABE-based access control mechanism and the content extraction signature scheme provides strong privacy preservation in data sharing. Security analysis shows that BPDS is a secure and effective way to realize data sharing for EMRs.
I. INTRODUCTION
EMR sharing could improve healthcare services, biomedical discovery, and costs, but fragmented systems create information islands while privacy, security, and interoperability remain difficult. BPDS addresses these issues with consortium blockchain, cloud storage, smart contracts, and content extraction signatures.
- Fragmented internal healthcare systems hinder EMR sharing and increase medical-service difficulty and expense.
- Privacy leakage can harm patients’ reputations and finances, while centralized systems face single-point-of-failure and arbitrary-modification vulnerabilities.
- Consortium blockchain is selected to control participating medical institutions while providing stronger privacy and lower costs than public blockchain.
- BPDS combines cloud-stored original EMRs, tamper-proof blockchain indexes, smart-contract sharing, and CES-based selective disclosure.
B. Improved DPoS
BPDS uses blockchain components and layered architecture to support privacy-preserving EMR acquisition, storage, sharing, and auditing. Its design combines DPoS consensus, cloud storage, consortium-blockchain indexes, CES, and smart contracts.
- B. Improved DPoS: DPoS provides blockchain consensus, while BPDS adapts node selection around medical institutions’ credit scores.The top 30 institutions become representative nodes and the next 20 become audit nodes.
- Smart Contracts: Smart contracts let patients predefine EMR access permissions, actions, and durations without an external trusted authority.
- System Architecture: BPDS has data acquirement, storage, and sharing layers for creating signed EMRs, storing records and indexes, and serving authorized users.Authorized patients, medical workers, and healthcare institutions can use records for health plans, treatment, or research.
- Data Storage Layer: Encrypted EMRs and extraction signatures are stored in the cloud, while indexes, permissions, and access activity are recorded on the consortium blockchain.Blockchain records support later auditing or investigation of access and leakage events.
B. Design Objectives
BPDS is designed to make EMR sharing private, controllable, tamper-resistant, and auditable. Patients retain control over access while system records support tracking of malicious entities.
- Patients participate in EMR-sharing transactions voluntarily and anonymously.
- Patients and data users register unique accounts that are not tied to identities in the cloud database.
- Blockchain-reserved EMR indexes cannot be changed by opponents.
- Blockchain records enable malicious entities to be tracked when data leakage is detected.
- Smart contracts let patients add or remove authorized users, restricting access to specified medical data.
C. Implementation of BPDS
BPDS acquires EMRs through doctor-generated CES signatures and patient-controlled storage and sharing. Its implementation encrypts records, verifies signatures, and supports selective extraction of seven medical-data components.
- Patients store EMRs in the cloud and submit their indexes with authorized-user lists to the consortium blockchain.The workflow gives patients control over their own EMRs and supports privacy-preserving sharing.
- Doctors use a key pair to generate CES signatures and a symmetric key to encrypt EMRs, while CP-ABE keys support secure cloud storage.
- CES divides EMRs into seven parts and defines a content extraction access structure to control which components can be extracted.The seven parts include identity, demographics, history, examination or laboratory results, and prescription information.
- The doctor signs each subdata hash and returns a full signature containing the extraction structure, tag, and component signatures.
- The doctor encrypts the signed message with Kdoc and encrypts Kdoc with the patient’s public key before sending both to the patient.
- The patient decrypts the key and message, verifies each component signature, and extracts a valid signature according to the chosen access structure.
3) Data Storing:
BPDS stores encrypted EMR data and extraction signatures in cloud storage while preparing extraction results from selected medical-data subsets. The process combines symmetric encryption with CP-ABE encryption and uploads the resulting ciphertexts alongside the extraction signature.
- CP-ABE encrypts each document key under the access-control policy before cloud storage.The corresponding ciphertext is E′_A(k_i), where A is the policy.
- The extraction process selects a medical-data subset from the content extraction access structure and constructs an extraction signature result.It derives subset-specific signature components and returns them with the access structure, selected indexes, timestamp, and extracted signatures.
- The patient generates a random document key and symmetrically encrypts each selected medical-data record with its hash and timestamp.The encrypted payload is E_ki(M_i∥h_i∥T).
- The cloud receives encrypted medical data, encrypted document keys, and the extraction signature, then returns each storage location.The uploaded triple is {E_ki(M_i∥h_i∥T), E′_A(k_i), δ_Ext}.
- The patient signs medical-record indexes and submits a timestamped sharing transaction request to the consortium blockchain.The request is associated with selected indexes and the patient’s signature on those indexes.
4) Data Release:
BPDS releases data through consortium-blockchain processing in which representative and auditing nodes validate transaction records. Smart contracts automatically execute permitted sharing operations when predefined access conditions are satisfied.
- A representative node verifies transactions, aggregates valid records into a data set, forms a signed and hashed block, and broadcasts it for auditing.The data set is expressed as Dset = {Req∥t}.
- Auditing nodes verify the proposed data block and return their audit results and signatures to the representative node.
- A new block is created when 51% of auditing nodes approve, after which the block and audit materials are broadcast to consortium nodes.Each representative node takes about 10 seconds to create a block, and a full cycle takes about 300 seconds.
- Smart contracts automatically execute predefined access rights, actions, and durations once the corresponding access conditions are met.The stated actions include reading, writing, and copying.
5) Data Sharing:
Data sharing begins with blockchain authentication and smart-contract authorization, then proceeds through encrypted index retrieval and cloud access. Users decrypt permitted records and verify extraction signatures before performing access actions.
- A data user submits an access request containing the target identity, object, and requested content, while the representative node records only legally authenticated requests.
- The smart contract returns encrypted EMR indexes when the request satisfies access conditions and denies the request otherwise.
- The user decrypts the returned message to obtain an index containing the cloud storage location, then retrieves the corresponding data object.
- CP-ABE retrieval fails when the user’s attribute set does not satisfy the embedded access policy; otherwise, it decrypts the document key and then the medical record.
- The user verifies each extracted signature against the recovered record, access structure, timestamp, and index before carrying out the access action.A failed verification indicates that the data might have been modified.
IV. SECURITY ANALYSIS
The security analysis evaluates BPDS across tamper-proofness, privacy preservation, secure data storage, and secure sharing. These are the stated security dimensions for the proposed system.
- The analysis covers whether BPDS prevents unauthorized modification of stored information.
- The analysis examines privacy preservation for EMR data and secure storage of the data.
- The analysis evaluates the security of EMR sharing within BPDS.
A. Tamper-Proof
BPDS makes EMRs tamper-proof by recording blockchain-linked data and access activity that cannot be arbitrarily modified and can be audited.
- EMRs in BPDS are immutable and cannot be modified arbitrarily.Changing blockchain records would require simultaneously controlling 51% of the network’s computational power.
- Each blockchain block links a current timestamp with the previous block’s hash, creating chronological protection against unauthorized changes.
- Access requests and activities are recorded on the blockchain so data changes can be audited and tracked.
B. Privacy Preservation
BPDS preserves EMR privacy through anonymous transactions, encrypted cloud storage, selective disclosure with content extraction signatures, and trusted consortium participation.
- BPDS uses random, transaction-specific public keys so transactions are anonymous and cannot be linked to the same user.
- Encrypted cloud storage reduces the risk of exposing original medical data while avoiding blockchain storage-capacity limitations.
- Content extraction signatures let patients remove sensitive portions from signed EMRs while preserving verifiability and limiting privacy leakage.Entities also cannot forge extraction signatures without the signer’s private key.
- An improved DPoS mechanism selects reputable medical organizations to support reliable data sharing in the consortium blockchain.
C. Data Secure Storing and Sharing
BPDS secures EMR storage and sharing through encryption, distributed cloud controls, tamper-proof blockchain indexes, authenticated release, and smart-contract access rules.
- BPDS secures the full process from EMR acquisition through sharing, while giving patients complete control over their records.
- Symmetric encryption protects the confidentiality and integrity of EMRs generated by doctors.
- Patients encrypt original EMRs for distributed cloud storage, with CP-ABE-based access control securing the medical data.
- Tamper-proof blockchain indexes, replicated transaction records, and digital signatures support reliable, authenticated, and traceable data release.Digital signatures provide authentication, integrity, and non-repudiation for each transaction.
- Smart contracts preset access permissions so only authorized users or institutions can use EMRs, with access records retained for tracing and revocation.