A Privacy-Preserving Cross-Domain Authentication and Key Agreement Scheme via Multiblockchains for Smart Cities

The requirement of devices to access data cross-domain in smart cities is expanding. The blockchain-based cross-domain authentication and key agreement (AKA) ensures the cross-domain data interaction security. However, the AKA scheme based on single-blockchain has the problem of high on-chain storage burden, risk of domain privacy leakage and inadequate privacy protection caused by the transparency of blockchain. Therefore, a multiblockchain-based cross-domain AKA scheme is proposed in this article. First, a multiblockchain model is designed to support cross-domain authentication. The model consists of two layers. The upper-layer blockchain records brief device identity information used for cross-domain authentication. The under-layer blockchain stores complete device identity information. Second, based on elliptic curve discrete logarithm problem (ECDLP) theory, cross-domain authentication is designed to meet the requirements of security of data exchange between blockchains, and meet the privacy-preserving. Finally, security analysis and performance analysis are conducted. The proposed scheme achieves better cross-domain data interaction security and privacy protection. These improvements are achieved with performance that outperforms single-blockchain-based schemes and is either comparable to or slightly better than multiblockchain-based schemes.