1. Introduction
Various advanced technologies are rapidly evolving and being invented, leading to the emergence of the metaverse concept, which is envisioned as the next iteration of the Internet. Metaverse is a virtual realm that parallels the physical world, where people engage with the metaverse using wearable devices (such as a virtual reality (VR)/augmented reality (AR) devices) and manipulate digital avatars to engage with others. Furthermore, the advancement of cutting-edge communication and networking technologies, including wireless networks and 5G technology, plays an important role in moving the metaverse forward by enabling low-latency, high-speed, and reliable data exchange between devices and the network. In addition, AI technology also contributes to automating the creation of virtual environments and digital items, and extracting valuable insights from the vast amount of data generated within the metaverse [
1,
2]. Blockchain, serving as a trust infrastructure in decentralized distributed networks, enables individual-centric digital asset transactions for metaverse users, not tied to traditional service providers’ platforms. It can also contribute to achieving the compatibility of individual services held by various virtual spaces (or service providers) within the metaverse [
3]. The metaverse is anticipated to bring about great innovation in various aspects of life, including e-commerce, medical, education, entertainment, smart factory and other social services [
4,
5].
In the metaverse, users can create avatars to represent themselves virtually, and they can access various services through these avatars. However, in the current metaverse application, users possess the freedom to create any avatar to serve as their virtual representation, irrespective of their real-world identity. This characteristic presents avenues for malicious users to fabricate a similar avatar and cause serious security problems, such as identity leakage, theft, and virtual asset fraud during avatar interactions. In addition, issues such as stalking, harassment, and sexual assault can pose a threat to users by manipulating the avatar, as well as the potential privacy threat of using AI technology to monitor users, make inferences about them, or engage in impersonation [
6,
7,
8]. Furthermore, users need to exchange their information and data with third parties to access services offered in various virtual worlds within the metaverse. However, due to the aforementioned characteristics, the identity information of the third parties using the user’s information is often unclear, making interactions for users challenging. Examples include qualifications to provide professional services such as medical or educational services, or adult verification to use certain data. Therefore, it is essential to design an authentication scheme that allow users to safely use services in the metaverse and remain secure from other security threats.
In current metaverse application, users have no direct means to verify the identity of other avatars as malicious or not, so they need help from the metaverse service provider. In the process of tracking these manipulators, the service provider mainly utilizes the manipulator’s account and password as clues to track the manipulator from a specific avatar identity [
9]. However, employing password-dependent methods means that any player who knows the account password can successfully gain access, so if a malicious user obtains the password illegally through various means, he/she can log in illegally and manipulate the avatar of a legitimate player. For more secure user identification and assurance on the metaverse, users can provide a lot of personal information to service providers. However, service providers that collect sensitive information, such as users’ voices and motions generated in the metaverse, can abuse this personal information and cause users’ privacy violations and huge losses through advertisements, personal tracking, fraud, illegal use, etc. In addition, the users and platform servers communicate through public channels in metaverse environments. Thus, an external adversary can attempt to eavesdrop and forge messages transmitted over public channels and attempt various security attacks, including masquerade, replay and man-in-the-middle attacks. Therefore, sensitive user information should not be disclosed to external parties and should only be shared with specific stakeholders in specific circumstances.
In this paper, we propose a blockchain-based authentication scheme that utilizes decentralized identifiers and verifiable credentials technology to enhance system security and protect users from various security and privacy threats. Decentralized identifiers and verifiable credentials enable trustworthy identity verification and data exchange without intermediaries. We propose an authentication scheme where users can authenticate not only avatars but also real manipulators during the authentication process required before interactions between avatars, using the users’ decentralized identifiers and verifiable credentials. Additionally, to ensure secure communication and avatar interactions in the metaverse environment, we propose an authentication method using blockchain between users and platform servers and between avatars. In our proposed scheme, the user and service provider establish security communication channels during the login phase through secure authentication and key agreement. Furthermore, we minimize user information exposed to service providers during interactions with other avatars and enhance user privacy protection by allowing only the necessary personal identification information for verification when interacting with different avatars in the metaverse.
Furthermore, in the metaverse, during the consensus process of validating and recording information on the blockchain, security attacks, such as 51% attacks and Sybil attacks, can occur [
10,
11,
12]. These attacks can undermine the trustworthiness of information recorded on the actual blockchain. However, in this paper, the consensus process occurs only once when the user initially creates a unique ID and registers it in the system. Subsequently, during the authentication process, users verify the required record information on the blockchain, and at this point, the blockchain’s consensus process does not occur, minimizing the consensus process. Additionally, this paper assumes the security of the blockchain consensus process and focuses on security threats and privacy issues during the user registration phase and subsequent use of metaverse services.
1.1. Contributions
The main contributions of paper are as follows:
In the metaverse environment, users are exposed to threats, such as fraud through fake avatars and the risk of personal information leakage during data transmission through open channels. We propose a secure authentication method for the metaverse environment to ensure security against various threats arising from fake avatars or vulnerabilities in wireless communication channels, and provide forward secrecy, anonymity, and privacy preservation.
The proposed scheme utilizes decentralized identifiers and verifiable credentials to enhance user privacy protection. Metaverse users can provide only the necessary identity information to stakeholders without disclosing their information to external parties, thereby safeguarding their personal information.
We perform an informal analysis to ensure that the proposed scheme can provide security against various attacks, including impersonation, session key disclosure, replay, man-in-the-middle, and insider attacks. Additionally, we show that the proposed scheme can achieve mutual authentication, perfect forward secrecy, anonymity and privacy preservation.
The security of the proposed scheme is analyzed by performing informal and formal analyses, such as Burrows–Abadi–Nikoogadam (BAN) logic, the real-or-random (RoR) model, and the automated validation of internet security protocols and applications (AVISPA) simulation tool. We also compare the performance and security features with the related works to show that the proposed scheme is superior.
1.2. Organization
The organization of the paper is as follows.
Section 2 reviews the existing authentication scheme applicable to the metaverse environment.
Section 3 introduces relevant preliminaries.
Section 4 presents a proposed system model and adversary model. The details of the proposed authentication scheme are depicted in
Section 5.
Section 6 analyzes the security of the proposed scheme in informal and formal proofs, and
Section 7 analyzes the computation and communication costs of the proposed scheme and related works. Finally, we summarize the conclusion and the future works in
Section 8.
2. Related Work
With the emergence of metaverse platforms (e.g., roblox and minecraft) and the increasing number of applications that utilize the metaverse, the security of the metaverse environment is discussed in several studies [
13,
14,
15]. According to the paper proposed by Vu et al. [
13], in the virtual world, users may find themselves in a situation where they are required to present identity information in order to obtain certain services and activities. They argued that not only are authentication mechanisms required to ensure that metaverse users can access the platform with appropriate identities but IoT devices in the metaverse infrastructure (e.g., sensors and UAVs) also need effective mechanisms for authentication during operation. They asserted that blockchain technology can address metaverse security and privacy issues, including identity and authentication management. Patwe and Mane [
14] argued the necessity of designing a secure authentication mechanism because impersonation, server spoofing, mutual authentication threats, and replay attacks can occur in the metaverse environment. And they proposed a blockchain-based architecture for avatar and user authentication in consideration of the decentralized nature of the metaverse. However, to date, there are no proposed specific system models and mutual authentication schemes for metaverse environments.
In the metaverse environment, where users use virtual services from the service provider’s server using wearable devices, such as VR and AR, some mutual authentication methods for the IoT environment can be applied. Panda and Chattopadhyay [
16] proposed an elliptic curve cryptography-based mutual authentication protocol to ensure secure communication between IoT devices and cloud servers. They argue that the proposed scheme is secure against various security threats (including impersonation attack, replay attack, etc.) by performing an informal analysis and using the AVISPA simulation tool. However, they did not consider the device-hijacking attack scenario. In the metaverse, there is a risk of maliciously capturing and tampering with a user’s XR device to extract sensitive information or impersonate a legitimate user to gain access to the system. Li et al. [
17] proposed a mutual authentication scheme based on blockchain for users and servers. Li et al.’s scheme solves the problem of SPoF that occurs in the centralized authentication structure by proposing a blockchain-based decentralized authentication scheme. They claimed that their scheme is secure against impersonation and man-in-the-middle attacks, and that it also provides perfect forward secrecy. However, security features such as insider attacks and anonymity are not covered. These schemes can be applied to authentication between a user’s device and a service provider’s server. However, it is difficult to apply these schemes to the authentication mechanism required for interactions between avatars in the metaverse environment. Ryu et al. [
18] proposed an authentication scheme that can ensure secure communication in a metaverse environment and transparently manage user identification data using blockchain technology. They designed the necessary mutual authentication methods to provide secure communication between platform servers and users as well as secure interactions between avatars. However, users who manipulate avatars in the metaverse need to prove their real-world information (e.g., age, gender, occupation and account) to other avatars in specific situations. Ryu et al.’s avatar authentication scheme can expose a lot of personal information of users to metaverse service providers. If personal information is exposed, it is possible to track the avatar’s user, or to impersonate a legitimate user by using a camouflage avatar.
Therefore, there is a need for research on authentication methods that can provide secure communication and privacy protection for users while considering the characteristics of the metaverse. We propose an authentication and key agreement scheme to enable metaverse users to securely utilize services from service providers. Furthermore, within the platform, we propose a secure authentication scheme between avatars that allows users to protect their privacy during avatar interactions without relying on the service provider.
5. Proposed Scheme
This section presents the proposed secure and privacy-preserving authentication scheme using a decentralized identifier for the metaverse. The proposed scheme includes the initialization, user setup, registration, login, and avatar authentication phases.
Table 1 describes the symbols used in the scheme.
5.1. Initialization Phase
First, initializes the system parameters. generates large prime numbers , an additive group G, elliptic curve over , a generator P, one-way hash functions , and a secret key , and it computes a public key corresponding to . After that, publishes the system parameters to the network.
5.2. User Setup
The user generates their own decentralized identifier.
issues a verifiable credential to the user that proves the user’s personal information. This phase is performed over a secure channel.
Figure 2 shows the user setup phase and detailed processes steps are as follows.
US-1: User inputs a unique , password and biometric information . Then, selects a random number as a private key and computes , , . Then, generates the ’s own that indicates the location of the DID document on the blockchain.
US-2: requests to issue a credential by sending , personal information . checks a ’s personal information and , and issues a verifiable credential that vouches for ’s personal information, such as occupation, age, etc. Then, sends to . After checking , computes and stores in the device.
5.3. User Registration Phase
User
registers with
using his/her own decentralized identifier.
verifies that the user’s decentralized identifier is valid, and then the user’s avatar is generated in virtual space. This phase is performed over a secure channel.
Figure 3 shows the user registration phase and detailed processes steps are as follows.
UR-1: inputs a identity , password , and imprints a biomatic information . Then, computes , , , , and send to .
UR-2: checks the validity of and retrieves from the blockchain. If it is valid, computes , and verifies . If the equation is correct, selects a random nonce and calculates , . After that, dispatches to and stores in a secure database.
UR-3: computes , , and stores in ’s XR devices.
5.4. Login Phase
When the user
attempts to access the
, the user and
authenticate each other. If mutual authentication between the user and
is completed and the session key is established, the user and
communicate using the session key to guarantee secure communication.
Figure 4 presents the login phase and the detailed processes of this phase are as follows.
LA-1: User first enters , , and . Then, computes , , , , , , and checks the . If the equation is correct, selects a random nonce and a current timestamp , and computes , . After that, sends to .
LA-2: generates a current timestamp and checks the freshness of the timestamp. Next, retrieves from the database using , and calculates , . checks the , and selects a random nonce and calculates , , , . After that, transmits to .
LA-3: After reception of the messages, checks the freshness of and computes , , . Then, checks the validity of , calculates , and updates with .
5.5. Avatar Authentication Phase
In the virtual space, user
can interact with other avatars
. For secure avatar-to-avatar interactions, the user provides the verifiable credentials proving the personal information to perform the avatar authentication phase.
Figure 5 shows the avatar authentication phase and the detailed steps are as follows.
AA-1: first sends a request including to . After reception of the request, retrieves using , and selects a random nonce and a current timestamp . Next, computes , , , , and sends to .
AA-2: After receiving the message , checks the validity of , and retrieves from the blockchain using . Then, computes , , and verifies the equation and the signature of the . Next, selects a random nonce and calculates , , , . And transmits to .
AA-3: Upon reception of message , checks the freshness of and computes , , . Finally, checks that is correct and verifies ’s signature .
8. Conclusions
In this paper, we propose a secure authentication scheme for metaverse environments to provide a secure avatar interactions and prevent against various security attacks. In our scheme, users can utilize DID and VC to prove their identity to other avatars in the metaverse without revealing irrelevant personal information to service providers. Furthermore, the proposed scheme provides a secure communication channel against various attacks through secure authentication and key agreement between the user and service provider. The proposed scheme is resistant to various security attacks (including stolen XR devices, offline password guessing, user and avatar impersonation, etc.) by performing the ROR oracle security analyses, the well-known AVISPA simulation, and BAN logic analyses. Next, the proposed scheme provides lower computation and communication costs than other related schemes for the metaverse environment by the comparison of computation costs and communication costs. Therefore, the proposed scheme can be applied to practical metaverse environments to provide high security and privacy preservation. In the future, we intend to research authentication protocols for a secure and trusted metaverse environment, taking into consideration potential security issues that may arise in the blockchain.