# Blockchain-Enabled Secure and Interoperable Authentication Scheme for Metaverse Environments
## 2 Related Work  
When Facebook changed its name to Meta in October 2021 [8], many researchers, organizations and industries started focusing on metaverse applications. Technology is no longer perceived to be limited to gaming and related applications. Many commercial metaverse platforms have evolved in the last few years. Many metaverses are built on Minecraft, Unity, Unreal Engine, Decentraland, Roblox, etc. Apart from that, many non-commercial metaverse environments are being created. However, security is a major concern in such metaverse worlds, as discussed in many papers [9; 10; 11]. In ref. [12], [PERSON] et al. proposed a secure authentication framework to guarantee the traceability of avatars in the metaverse using a two-factor authentication framework based on chameleon signatures and biometrics. It uses blockchain as a solution for traceability. However, some of the identity-related security issues in metaverse environments are not considered by this framework. For example, cross-metaverse-identity interoperability is not addressed, and server-spoofing attacks are not handled. Also, avatar-to-device mutual authentication is not considered. The framework's communication and computation costs can be reduced further. In ref. [13], [PERSON] et al. discuss in detail various security- and privacy-related issues in metaverse environments, including personal information leakage, eavesdropping, phishing, broken authentication, and so on. Paper [14] emphasizes the importance of enabling blockchain for various metaverse applications. The potential of blockchain for security and privacy aspects of the metaverse infrastructure is also mapped out in this paper. [PERSON] et al. in ref. [15] proposed a metachain framework for the interoperability of metaverse service providers and metaverse users. They have added a smart contract mechanism and novel sharding scheme to achieve the same outcomes. In paper [16], [PERSON] et al. propose a secure mutual authentication protocol for IoT and cloud servers based on elliptic curve cryptography. Though the research covers attacks like device privacy, impersonation attacks, replay attacks, password-guessing attacks,and mutual-authentication attacks, there is scope to improve computational time and computational overheads. Also, the solution is designed for IoT environments and is not specific to cross-metaverse environments. Identity interoperability is also not addressed in the research. Paper [17] by [PERSON], [PERSON] et al. discussed an authentication protocol based on elliptical curves and bilinear pairs. However, there is scope to improve the computational and communication costs of the protocol. [PERSON] et al. focused in ref. [18] on addressing impersonation, replay, server-spoofing, stolen-smart-device, man-in-the-middle (MITM), and insider attacks. However, identity interoperability is not discussed. Also, avatar-to-device mutual authentication is not in their scope. [PERSON], [PERSON] et al. in paper [19] proposed a blockchain-enabled authentication scheme. Their approach mitigates certain security and privacy concerns in the metaverse environment. In ref. [20], [PERSON] et al. discuss an efficient block-chain-assisted secure device-authentication mechanism, BASA, for cross-domain IIoT. A comparison of the similar solutions proposed in the literature is as shown in Table 1.  
From the literature, it is clear that there is a need to build a secure and interoperable authentication scheme using blockchain for the cross-metaverse platforms that will cover not just avatars but device identity as well. Also, it should map the physical identity of the physical user to the avatar's virtual identities. Such an identity mechanism should not be specific to one platform but should allow meta-persons to navigate across different metaverses. This identity mechanism should address a greater number of identity-related security issues compared to the competitive work available.