In the age of technological advancement, collaborative e-healthcare emerges as a transformative system eliminating traditional location and accessibility barriers in healthcare services. Here, searchable encryption (SE) plays a key role in enabling healthcare providers to outsource encrypted medical data and search services to third parties like cloud servers, thereby reducing storage and management expenses. This intermediary approach poses challenges of single-point failure, privacy breaches, and potentially untrustworthy results. State-of-the-art public key-based SE methods use a cloud-assisted architecture that doesn’t support reliable and practical searches with fine-grained permissions. Also, such systems require additional support to address potential privacy leakages and ensure data availability at the storage server. To address these concerns, we propose a blockchain-assisted efficient and secure keyword search (BESKS) scheme to enforce fine-grained keyword search privilege control while achieving practical search complexity. Our scheme employs a ciphertext-policy attribute-based keyword search mechanism where keywords are encrypted using expressive access policies to build an inverted index structure. The encrypted indexes are stored on the blockchain while encrypted medical documents are stored on InterPlanetary File System (IPFS) nodes to enhance availability and ensure the reliability and scalability of our approach. Our scheme utilizes blockchain-based smart contract for efficient, secure search operations and ensures financial fairness in fine-grained searches. Search tokens are generated based on user attributes and query keywords to facilitate private searches on-chain. To enhance the search process, our secure index enables exact match for a query keyword in constant time to ensure expensive authorization operations are performed only once. Theoretical analysis suggests that our BESKS is more efficient and secure than state-of-the-art schemes. Prototype implementation results on the Ethereum blockchain network further validate its feasibility for real-world applications, demonstrating the scheme’s practical applicability in collaborative e-healthcare systems.

Ciphertext-Policy Attribute-Based Encryption (CP-ABE) is a cryptographic primitive that provides confidentiality and fine-grained access control for data sharing in untrusted cloud environments. It allows data owners to set access policies based on attributes, ensuring only users who meet the criteria can decrypt and access the data. However, existing CP-ABE systems are inherently designed for static attributes and lack efficient support for dynamic user attributes, often necessitating frequent key updates and complex revocation processes. To address these challenges, we propose an enhanced CP-ABE cryptosystem that allows for the dynamic generation of additional key components, which can be efficiently integrated with the user's existing key. The user private key is assigned attribute-level expiration tags, facilitating instant revocation. Additionally, our scheme facilitates the secure offloading of partial decryption of ciphertext to the cloud server using a transformed private key, thus reducing the computational overhead on resource-constrained user devices. Our proposed cryptosystem provides a secure and scalable approach for managing dynamic attributes in cloud environments with rapidly evolving access requirements.

Cloud-assisted Internet of Things (CIoT) enhances data accessibility and operational efficiency but encounters various security and privacy challenges. Today, CIoT applications generate large amounts of data in a multi-client accessible environment involving periodic addition of data. These systems require efficient searchable encryption to securely share data with authorized users, enable private keyword searches, and support frequent updates to outsourced data, thus maintaining data integrity and user privacy. Existing symmetric searchable encryption (SSE) schemes enable efficient searches for large datasets but are limited in providing multi-user data sharing. In contrast, attribute-based searchable encryption (ABSE) schemes offer fine-grained access control in collaborative scenarios but suffer from high search latency. In this paper, we present a hybrid searchable encryption scheme that enables secure keyword search with sublinear search efficiency and supports periodic dynamic addition of files in multi-client IoT environments. By providing privacy-preserving keyword searches with forward privacy and keyword-level access control, our approach effectively enhances security and performance for cloud-assisted IoT.