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Universal Subscriber Identity Module (USIM) is an essential part of the mobile network mainly for providing identification and authentication of the subscriber. The activation and deactivation of USIMs are the two most critical services that must be supported by Mobile Network Operators (MNOs). The current solutions suffer from several limitations such as the lack of round-the-clock services and the presence of a single point of failure. In this paper, we propose a blockchain-based scheme for USIM management. Each MNO creates its own smart contract and publishes its address to subscribers. Subscribers can then directly submit their requests by registering a transaction that invokes a specific function of the smart contract. The proposed scheme provides an anytime-anywhere service while at the same time it leverages the benefits of blockchain technology, such as a decentralized architecture that prevents Denial-of-Service (DoS) attacks, as well as a secure auditable log and payment using cryptocurrency. Moreover, we provide a security proof for the scheme through formal verification. Our results demonstrate that our scheme ensures subscriber privacy while providing mutual authentication among participants. Finally, our evaluation on the Ethereum blockchain confirms the efficiency of the scheme in terms of both transaction and execution costs.

Subscriber authentication is a primitive operation in mobile networks required by each operator prior to offering any service to end users. In this paper, we propose a novel blockchain-based Authentication and Key Agreement (AKA) protocol for roaming services in 5G networks. Each Home Network (HN) creates its own smart contract and publishes its address to inform other operators who want to offer roaming services to HN subscribers. All subsequent communication between the HN and Serving Network (SN) is done by calling the function of this smart contract. The proposed protocol eliminates the need for a secure channel between the HN and SN, which is a primary requirement of current 5G AKA protocols. In practice, a secure channel requires the HN and SN to establish a secure session before running the AKA protocol. Further, the proposed protocol leverages the benefits of blockchain, such as auditable log, decentralized architecture, and the prevention of Denial of Service (DoS) attacks. Furthermore, we provide a security proof of the protocol through formal verification using ProVerif. The results show that our scheme tends to preserve user privacy and at the same time provides mutual authentication of the participants. Finally, our evaluation of the Ethereum blockchain shows that the protocol is efficient in terms of both transaction and execution costs.