# A Blockchain-Assisted Security Protocol for Group Handover of MTC Devices in 5G Wireless Networks
## 2 Related Work  
To address the challenges posed by the technologies in 5G wireless networks, the authors in [5] employed aggregated message authentication codes (AMAC) to reduce signaling overheads. By this approach, the group leader aggregates message authentication codes (MACs) from all group members and sends the aggregated information to the network. However, the protocol fails to ensure user privacy because the messages are transmitted in plain text over insecure channels. The solutions in [6; 7] need bilinear mapping calculations, which can result in higher computational costs. In [6], a lightweight and efficient group authentication protocol is proposed. This scheme integrates bilinear mapping and aggregate certifiateless signature mechanisms to address the real-time secure and efficient access of multiple MTCDs. In [7], a multi-user access authentication scheme has been proposed, which leverages the features of a network architecture combining Mobile Edge Computing (MEC) and Software-Defined Networking (SDN) to perform pre-authentication by predicting a potential target base station for handover. However, this system architecture introduces deployment challenges in practice, and it involves modular exponentiations, which need higher computational costs. In [8], a lightweight group identity authentication scheme is proposed, suitable for both centralized and decentralized settings. It enables all MTCDs to negotiate and generate a group key as a session key for mutual communication. However, this scheme is susceptible to DoS attacks and has high energy consumption when using bilinear pairings. In [1], a privacy-preserving handover authentication protocol suitable for a group of MTCDs in 5G networks is proposed. The protocol aims to reduce signaling costs by aggregating messages from two MTCDs with an aggregated MAC and sending them through an authenticated group member. However, this scheme is susceptible to DDoS attacks. The solutions in [9; 10; 11; 12; 13] all employ blockchain-based techniques for identity authentication. Among them, ref. [9] introduces a blockchain-based protocol to achieve mutual authentication and session key negotiation for vehicles. It is accomplished by introducing an auxiliary blockchain and a parent blockchain, along with the use of an Interplanetary File System (IPFS) to collaborate in information storage. The authentication process by this scheme incorporates elliptic curve cryptography (ECC) and one-way hash functions. The introduction of multiple blockchains may lead to unnecessary resource consumption. Ref. [10] presents a group-based handover authentication scheme for 6G heterogeneous networks, leveraging blockchain for storing authentication information and utilizing aggregate signatures for streamlined batch user authentication. Ref. [11] introduces a collaborative authentication scheme using blockchain in heterogeneous networks. This scheme improves the SM9 algorithm and proposes a verifiable user identity legitimacy through group signature, eliminating data redundancy caused by unfiltered blockchain information in wireless communication. Ref. [12] proposes a lightweight blockchain-based initial and handover authentication protocol for vehicles and infrastructure. This protocol involves vehicles performing lightweight calculations using hash and XOR operations, and the information required for handover authentication is stored in Roadside Units (RSUs) through secure sharing within the consortium blockchain. It can revoke unauthorized vehicles directly using blockchain without the need for a third-party entity. Ref. [13] presents a blockchain-based group key distribution method, distributing and updating group session keys among group members using smart contracts for identity authentication. The authors in [14] have proposed two protocols tailored to different security requirements. However, these protocols are only applicable to scenarios with a predefined trajectory. Ref.