ACTA: A Verifiable Accountable Decryption Mechanism for Secure and Auditable Blockchain-Based Data Sharing

The implementation of the secure credential management systems requires the exchange and sharing of sensitive records along with the strict access control, confidentiality, and accountability requirements. However, the sharing of the credentials is associated with security and privacy concerns. While there are many blockchain solutions that enable immutable audit trails and decentralized trust, the existing approaches provide limited support for verifiable accountability and controlled decryption mechanisms that are needed for the secure handling of sensitive data. This paper proposes a novel framework called Accountable Confidential Trusted Access (ACTA) that offers verifiable accountable decryption and combines the use of blockchain and trusted execution environments (TEEs). In addition, ACTA incorporates Interplanetary File System (IPFS) for off-chain encrypted record storage and maintains its integrity validation with on-chain content identity identifier (CID) and cryptographic hash values. ACTA is based on the three-phase secure process, which includes the linkage of the access authorization, encrypted data, and enclave-execution of the decryption while storing the immutable audit records on the blockchain. Following a successful decryption operation, ACTA records verifiable evidence that an authenticated requester obtained the encrypted record bound to their authorization and that the operation was executed by a registered enclave, without publishing any value derived from the plaintext. Experimental results obtained with Hyperledger Caliper, averaged over four independent runs, indicate that ACTA sustains a peak of 16.82 TPS for certificate issuance and 16.45 TPS for the complete accountable-decryption workflow across offered loads from 2 to 25 TPS, with average end-to-end latency decreasing from 1212 to 295 ms and from 1092 to 222 ms, respectively, as the offered load increases. Storing ciphertext in IPFS reduces on-chain state growth while the accountable-decryption path remains within the same order of magnitude of latency as the issuance path. In addition, security analysis shows that ACTA is resilient to several types of attacks. The proposed framework provides a scalable solution for accountable decryption in blockchain systems without sacrificing confidentiality, integrity, or decentralized trust.