Federated Time-Bound Blockchain-Based Revocation with Ciphertext-Policy Attribute-Based Encryption and Redundant Shard Reassembly

Ensuring data security, access revocation, and cost efficiency during data exchange becomes paramount in secure cloud computing. This study presents a secure data sharing framework that integrates Federated Time-Bound Ciphertext-Policy Attribute-Based Encryption (FTB-CP-ABE) along with blockchain-based revocation. On top of it, data is stored with fault-tolerant redundant sharding. The proposed FTB-CP-ABE enables data owners to define access policies and allows multiple attribute authorities to issue time-bound decryption keys in a decentralized manner. To enhance data security, encrypted data is divided into chunks (shards) using threshold secret sharing, which allows an authorized user to recover data even if some shards are lost. Blockchain is used to enforce transparent revocation and maintain audit trails, which allows logging keys that are revoked and why. In the decryption process, the user's key ID is checked against the ledger, and if the status is revoked, the system denies decryption even if the CP-ABE policy matches. The proposed multilayer framework provides auditable fine-grained access control in untrusted cloud environments.