2022 IEEE Smartworld, Ubiquitous Intelligence & Computing, Scalable Computing & Communications, Digital Twin, Privacy Computing, Metaverse, Autonomous & Trusted Vehicles (SmartWorld/UIC/ScalCom/DigitalTwin/PriComp/Meta) | 979-8-3503-4655-8/22/$31.00 ©2022 IEEE | DOI: 10.1109/SmartWorld-UIC-ATC-ScalCom-DigitalTwin-PriComp-Metaverse56740.2022.00340
2022 IEEE Smartworld, Ubiquitous Intelligence & Computing, Scalable Computing & Communications, Digital Twin, Privacy
Computing, Metaverse, Autonomous & Trusted Vehicles (SmartWorld/UIC/ScalCom/DigitalTwin/PriComp/Metaverse)
Yingying Yao
Beijing Key Laboratory of Security and
Privacy in Intelligent Transportation
Beijing Jiaotong University
Beijing, China
yyyao@bjtu.edu.cn
Xiaolin Chang
Beijing Key Laboratory of Security and
Privacy in Intelligent Transportation
Beijing Jiaotong University
Beijing, China
xlchang@bjtu.edu.cn
Lin Li
Beijing Key Laboratory of Security and
Privacy in Intelligent Transportation
Beijing Jiaotong University
Beijing, China
lilin@bjtu.edu.cn
Jiqiang Liu
Beijing Key Laboratory of Security and
Privacy in Intelligent Transportation
Beijing Jiaotong University
Beijing, China
jqliu bjtu.edu.cn
Computer Science Department
Ryerson University
Toronto, Ontario, Canada
jmisic@ryerson.ca
Computer Science Department
Ryerson University
Toronto, Ontario, Canada
vmisic@ryerson.ca
Abstract The recent advances of emerging technologies
including artificial intelligence, 5G, 6G, extended reality and
blockchain promote the rapid development of next-generation
Internet. As an evolving paradigm of next-generation Internet,
metaverse, a fully immersive, hyper spatiotemporal and selfsustaining virtual shared space, is moving from imagination to
the coming reality. However, its massive data flow, pervasive
user profiling activities and other intrinsic features can lead to
a lot of security and privacy concerns, which will hinder its
further deployment. Specially, since the identities of
users/avatars in the metaverse can be illegally stolen,
impersonated, and interoperability issues can be encountered in
authentication across metaverses, this paper designs a
lightweight and privacy-preserving seamless cross-metaverse
authentication and key agreement scheme named MetaverseAKA to meet the challenges. Metaverse-AKA can not only
realize the seamless cross-metaverse authentication but also
assure the users
privacy by achieving the anonymity and
unlinkability. In addition, Metaverse-AKA also has the
following advantages: (i) Realizing the traceability for users in
physical world. (ii) Resistance to multiple attacks like
impersonation attack, man-in-the-middle attack and replay
attack. (iii) Adopting lightweight cryptographic primitives and
having better performance through experiment verification and
comparison.
Keywords metaverse, privacy-preserving, cross-metaverse
authentication, lightweight, seamless
I. INTRODUCTION
Metaverse is a virtual shared space integrating physics,
human beings and the digital world. It takes digital life as its
basic form. Metaverse is defined as a large-scale interoperable
network of real-time 3D virtual world in some studies [1].
2021 can be called the first year of the metaverse. In this year,
relevant elements in the meta universe are gathered. And in
October of the same year, Facebook officially changed its
name to Metaverse. The metaverse has gradually become a
new specification for social networks and three-dimensional
(3D) virtual worlds, where users can live like digital natives
and experience another life in the virtual world. In addition to
the field of social networks, it has great potential in the
industrial, commercial, educational, medical, military and
government sectors [2].
Although metaverse has great development potential and
bright prospects, security and privacy issues will be the main
issues that limit its further development [3]. In this paper, we
focus on the threats to authentication in metaverse. Firstly, the
identities of users/avatars in the metaverse are at risk of being
illegally stolen, which can be more serious than that in
traditional information systems since the identity is related to
is associated with vital private information including digital
life, digital assets, social relationships and so on. Once the
identity in metaverse is stolen, these vital private information
will also be disclosed. In Opensea non-fungible token (NFT)
were attacked,
marketplace, 17 users
resulting in a loss of $1.7 million in 2022 [4]. Secondly, the
authorized users in metaverse may be subject to
impersonation attack. When an authorized user is carried out
impersonation attack by an attacker, the attacker can access
the services of the metaverse and leverage the user's legal
identity to do illegal things in virtual world. For example,
attackers impersonate trusted endpoints through Bluetooth
impersonation attacks [5] and insert a malicious wearable
device into the established Bluetooth pairing to gain illegal
access to the metaverse services. Thirdly, it is very important
for users/ avatars to conduct trusted and interoperable asset
exchange and seamless avatar transfer in different metaverses,
for example, between Roblox and Fortnite. In addition, the
identity authentication across distinct metaverse (services run
by distinct virtual service providers) is critical to deliver
seamless metaverse services for users. Thus, ensuring
lightweight
and
trusted
cross-metaverse
identity
authentication is a challenge for the widely deployment of
metaverse.
A lot of cross-domain authentication schemes in different
fields have been put forward, for example, Shen et al. [6]
proposed a blockchain-assisted secure device authentication
979-8-3503-4655-8/22/$31.00 ©2022 IEEE
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for cross-domain industrial Internet of Things, and Chen et al.
[7] put forward the XAuth which is an efficient privacypreserving cross-domain authentication scheme based on
public key infrastructure. However, the existing cross-domain
authentication schemes in different fields did not consider the
key characteristics of metaverse and cannot directly be
directly applied to the identity authentication of metaverse.
The technology of identity authentication for metaverse is still
in the exploratory stage and is a promising topic [3].
Therefore, facing the above mentioned authentication
challenges in metaverse, this paper designs a lightweight and
privacy-preserving seamless cross-metaverse authentication
and key agreement scheme (Metaverse-AKA). The
contributions of this paper are as follows.
quickly due to that VCs are digital and signed by a trusted
authority. VC is more suitable for long-distance mutual trust
building [8].
C. Elliptic-Curve Cryptography (ECC)
Let denote a large prime integer,
be an cyclic group
with generator (base point) , and its order is .
Elliptic curve discrete logarithm problem (ECDLP)
[10]: Given two points
, finding an
such
that
is computationally infeasible.
III. SYSTEM MODEL AND THREAT MODEL
This section details the system model and threat model of
our proposed scheme.
1) Metaverse-AKA scheme provides the services of
mutual authentication and seamless cross-metaverse
authentication.
A. System Model
The simplified system model is shown in Fig.1, and it
includes three entities, which are users, avatars and the
metaverse. Their roles and responsibilities are as follows.
2) Metaverse-AKA scheme assures
achieving the anonymity and unlinkability.
3) Metaverse-AKA scheme realizes the traceability. The
users whose avatars in virtual world have illegal behavior like
money laundering can be traced in physical world.
4) Metaverse-AKA scheme can withstand the well-known
security attacks including impersonation attack, man-in-themiddle attack, replay attack.
5) Metaverse-AKA scheme is lightweight through
adopting simple cryptographic primitives and achieving
seamless cross-metaverse authentication.
The structure of the rest paper is as follows. Section II
introduces the preliminaries. Section III describes the system
model and threat model. The details of our proposed
Metaverse-AKA scheme are presented Section IV. Section V
analyzes the features of security and evaluates the
performance of Metaverse-AKA scheme. Section VI
summarizes the whole paper.
II. PRELIMINARES
Fig. 1. System model
This section introduces the concepts used in our proposed
scheme.
Trusted Issuer (TI). TI is fully trusted and it offers root
of trust for the system. At the same time, TI is responsible for
issuing VCs for users.
A. Decentralized Identifiers (DID)
DID is a type of decentralized identifier without a
centralized trusted issuer. DID is generated and controlled by
the users themselves, which makes a user have full control
and ownership his/her identity [8]. And a user can generate
multiple different DIDs to be used for different applications
or activities to prevent being tracked. A DID of a user can be
parsed into a DID document, which contains information
describing the user, f
public key. W3C
[9]. For more information
about DID, please refer to the standard.
User (U). Users wearing smart wearable devices such as
VR/AR helmets can control their digital avatars through
extended reality (XR) and human-computer interaction (HCI)
technologies to socialize, work, play and interact with other
avatars or virtual entities in the metaverse.
Avatar (A).
metaverse. And users can create various avatars in different
sub-metaverses. In addition, an avatar can cross different submetaverses for different metaverse services.
B. Verifiable Credential (VC)
Since there is no centralized trusted issuer of the identities
and the DID is generated by the user, a proof is required to
verify the validity of the DID. VC can provide the function of
the proof. And it is tamper-resistant, reliable and transmitted
Metaverse. The metaverse can consist of multiple
interconnected distributed sub-metaverses (SMs), and each
sub-metaverse can provide specific kinds of virtual
environments, virtual services and virtual goods for avatars,
for example, virtual cities, virtual museum, NFT and so on.
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More details about the architecture and components of the
metaverse can refer to ISO/IEC 23005 [11] and IEEE 2888
standards [12]. When an avatar would like to enjoy the
services, the sub-metaverse needs to authenticate it.
stored in its DID document, which is recorded on the
blockchain. Finally, TI keeps
secretly and publishes the
public parameters
.
B. Threat Model
The threat model adopted in this paper is CK-model [13].
In the model, the main objective of the attacker is to gain
unauthorized access to the metaverse. And the attacker tries
to acquire sensitive information through passive or active
attack on the communicated information between the
communication parties through the common channel. The
attacker can monitor all traffic on the Internet. In addition, the
following conditions are also considered.
B. Registration Phase
This phase focuses on the registration process of users and
sub-metaverses, which is only executed once. Here we take
and
as representation to introduce the registration
process.
1) User Registration
In this phase, the user
register with TI to obtain the
VCs of his/her identities and public key, and the
communication is through a secure channel.
For each sub-metaverse, unique keys are used to limit
the damage of an attack.
Firstly,
The sub-metaverses can collide with each other, but
determining the true identity of a user is impossible.
, and then randomly selects
as its
private key and computes its corresponding public key
. Then it submits the message
A pseudo-identity cannot link to the DID, and the
different pseudo-identities cannot be linked to a same
user.
containing its real identity
IV. USING THE TEMPLATE
This section details our proposed scheme, which consists
of seven phases: Initialization Phase, Registration Phase,
Avatar Creation Phase, User Login Phase, Mutual
Authentication Phase, Cross-Metaverse Authentication Phase,
and Tracing Phase. TABLE I gives the symbols used in our
scheme. The description of each phase is as following.
TABLE I
generates a set of unlinkable pseudo-identities
RIDU i , a set of pseudo-identities
and current timestamp
keeps its private key
to TI. At the same time,
secretly.
When receiving the message
authenticity of the real identity
timestamp
SYMBOLS
, public key
from , TI verifies the
and the validity of the
. If they check pass, TI first calculates
and signs and
with its private key
to get the signature
. Then TI
calculates
signs
,
and
with its private key
signatures
returns
,
and
to
and
and
to get the
. Then TI
, where
. At the
same time, TI stores the tuple
.
After receiving the
denoted as
denoted as
private key. Its corresponding public key
containing its public key is
2) Sub-metaverse Registration
Similarly, the communication between the sub-metaverse
and TI is also through a secure channel during the
registration process.
. After that, TI generates its DID
, and then randomly selects
generates its DID
stored in its DID document, which is recorded on the
blockchain.
A. Initialization Phase
To initialize the system, firstly, TI inputs security
parameter
to generate a cyclic group
with base point
and prime order q , and initialize a cryptographic hash
function
. The
,
as its
is
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Firstly,
key
randomly selects
and
as its private
computes its corresponding
. Then it submits
containing its real identity
public
, which is stored in
key
device.
D. User Login Phase
When a user
would like to enter a sub-metaverse
using the avatar
,
needs to input his/her DID
, public key
and current timestamp
to TI. At the same time,
keeps its private key
secretly.
, password
When receiving
from
TI verifies the authenticity of the real identity
and biometrics
smart wearable device to initiate the login request.
,
Firstly,
and the
inputs
,
validity of the timestamp
. If they check pass, TI
calculates
and signs
and
with
wearable device calculates
its private key
the device will check if
,
to get the signature
. Then TI returns
.
denoted as
,
. The
,
generates its DID
containing its public key is
chooses
a
pseudo-identity
and
, parameters
the
,
Then
and
to
same session key
securely.
and returns
from
,
and
of the created avatar by
to enjoy the metaverse services in
F. Cross-Metaverse Authentication Phase
When the user
would like to move its avatar
from sub-metaverse
to another sub-metaverse
. To
realize the seamless access metaverse services in other submetaverse, the cross-metaverse authentication process needs
to be performed.
computes
. Then the parameter
in
, the device computes
holds. If the equation does not hold, the process
will be terminated. Otherwise, the mutual authentication is
finished and
can communicate with
through the
.
After receiving
returns the message
.
and checks if
.
stores
and
verifies
,
,
satisfies. If the
n 2 ) . After that,
calculates
Ui
then it check if
to the device of
by searching the DID of TI on the blockchain. After
successful
verification,
[VC TI ]x
. And
After receiving
,
first calculates
and
compute
sends
through a secure channel.
When receiving the request and
,
.
equation does not hold, the process will be terminated.
Otherwise,
will randomly choose
, and
set
with an avatar creation
request to
to
When receiving
, and
. After that,
, extracts
. After that, it sends
the message
. Then
from
satisfies. If
, and calculates
, a random number
and inputs its biometrics (e.g., iris)
, and then
. Then, it randomly selects
C. Avatar Creation Phase
This phase is the process of a user creating an avatar in a
sub-metaverse. Still, we take
and
as representation
to introduce this process.
chooses a password
, the smart
E. Mutual Authentication Phase
After
initializing the smart wearable device, the
device search the blockchain to get the DID of
, that is
stored in its DID document, which is recorded on the
blockchain.
Firstly,
and
the equation holds, the smart wearable device is initialized.
to
After receiving the
into his/her
is
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Firstly,
searches the blockchain for the DID of
that is
,
, and then it randomly selects
which requires the attacker can get the
and
and biometrics
to
through the secure channel established with the
session key
.
of
Secondly, only TI knows the real identity of the user
in the scheme, and TI is fully trusted issuer, who is assumed
not to disclose any information of users. And all the SMs
cannot obtain any identifiable information of a user, including
utilizes the public key
stored in
to encrypt
and obtains the ciphertext
. After that,
the unlinkable pseudo-identity PDID through
sends
to
. At
the same time, it returns a confirmation message to
Then
and decrypt the ciphertext
.
ciphertext
and calculates its
Acquiring the private key is infeasible for the attacker
according to the ECDLP.
using
Afterwards,
sends the message
in mutual
authentication phase and cross-metaverse authentication
phase respectively. Even if a sub-metaverse
discloses
the current PDID of the user to an attacker, the attacker still
requires
and private key
to construct
.
computes
. After that, it randomly selects
. It is very difficult for the
attacker to obtain these information, especially biometric
information like iris.
sends a cross-metaverse request
After receiving the request,
of
, password
to
Therefore, the proposed Metaverse-AKA scheme is
resistant to impersonation attack.
and calculates the session key
.
2) Resistance to man-in-the-middle attack
will use its private key
received from
to decrypt
Since an attacker can listen to all exchanged messages
between users and SMs on the public channel, there is risk of
man-in-the-middle attack. In Metaverse-AKA scheme, the
exchanged messages over public channel between a user
and a sub-metaverse
include
and
. Then it calculates
and compares it with
received from
. If
they are equal, it will continue using its private key
decrypt
received from
key with
, that is
In this way,
to
in mutual authentication phase. The attacker
can obtain and understand the values in the above messages,
where
,
and calculate the same session
.
and
can use the new session key
and
sk ' that only they know to communicate securely.
. However, the
SM j
G. Tracing Phase
When an avatar has some illegal behaviors, for example,
money laundering, the SM will furnish the
,
value of and
cannot be acquired by the attacker, who
cannot utilize the values to compute the parameters to reply
the communication parties and also cannot get the exchanged
messages encrypted with .
and additional evidence to TI for arbitration. TI will find the
tuple
to trace and
Therefore, Metaverse-AKA scheme is resistant to man-inthe-middle attack.
3) Resistance to replay attack
punish the user in physical world.
The attacker may try to utilize the previously sent message
to perform replay attack. Also during the mutual
authentication phase and cross-metaverse authentication
phase, the messages that can be replayed include
,
,
V. SECURITY AND PERFORMANCE ANALYSIS
This section first discusses the features of MetaverseAKA in terms of security and privacy. Then the performance
is evaluated.
A. Security Analysis
The proposed scheme satisfies the following features of
security and privacy.
and
. But even if the attacker
replays the above messages to the communication parties, it
still cannot get
, ,
and n 4 to compute
and
1) Resistance to impersonation attack
. The process will be terminated.
Firstly, if an attacker wants to impersonate a legitimate
user
, it needs to first log on the smart wearable device,
sk
Therefore, Metaverse-AKA scheme is resistant to replay
attack.
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Authorized
times on the experiment platform. The average execution time
of each operation is presented in TABLE III.
4) Anonymity, unlinkability and treaceability
Firstly, as mentioned above, only TI knows the real
identity of the user
in the scheme, and TI is fully trusted
issuer, who is assumed not to disclose any information of
users.
TABLE III COSTS OF CRYPTOGRAPHIC OPERATIONS (MS)
Symbols
Secondly, each avatar of a user has its own PDID with
unique VC in avatar creation phase. Thus the PDIDs cannot
link to each other and also cannot be link to the DID of the
user. In addition, SMs can get the PDID through
PDIDUx i h5
and decrypt the
ciphertext
in mutual authentication phase and crossmetaverse authentication phase respectively. Even if SMs
collude, they only can get the avatars corresponding to the
Costs
0.698
Hash operation (SHA-256)
0.000508
Signature generation (ECDSA)
0.10265
Signature verification (ECDSA)
0.10305
Asymmetric encryption (EC-ElGamal)
1.458
Asymmetric encryption (EC-ElGamal)
0.729
Exclusive OR
-
2) Computation Overhead
In Initialization Phase, TI needs to perform one point
scalar multiplication operation, that is
ms. The
users and SMs have no operations.
to a same user.
Thirdly, according to the introduction of tracing phase in
Section IV.G, the users with illegal behaviors can be traced.
In Registration Phase, TI needs to perform
hash
operations and
signature generation operations, that
is
ms. A user and
a SM all need to perform one point scalar multiplication
operation, that is
ms.
Therefore, the proposed Metaverse-AKA scheme satisfies
anonymity, unlinkability and traceability.
5) Seamless cross metaverse
As the description in Section IV.F, when an avatar of a
user wants to access services of another sub-metaverse, it
does not need to repeat the mutual authentication process. The
current SM will assist the avatar to establish a new session
key with another SM and the current SM cannot know the
session key, which realizes the seamless cross metaverse and
new communication secrecy.
In Avatar Creation Phase, TI has no operations. To create
an avatar, a user needs to perform three hash operations and
two exclusive OR operations, that is
ms.
A SM needs to perform four hash operations and one
exclusive OR operation, that is
ms.
Therefore, Metaverse-AKA scheme realizes seamless
cross metaverse.
In User Login Phase, TI and SMs have no operations. A
user also needs to perform three hash operations and two
exclusive OR operations, that is
ms.
B. Performance Analysis
This sub-section first measure the cryptographic
operations used in Metaverse-AKA scheme. Then we
evaluate the performance of our proposed scheme in terms of
computation, and communication overhead to illustrate that
Metaverse-AKA scheme has better efficiency.
In Mutual Authentication Phase, TI has no operations. A
user also needs to perform four hash operations and two
exclusive OR operations, that is
ms. A
SM needs to perform five hash operations and one exclusive
OR operation, that is
ms.
1) Experimental settings
We measure the basic cryptographic operation on a
personal computer, the configurations of which is presented
in TABLE II.
TABLE II
Operations
Point scalar multiplication in
In Cross-Metaverse Authentication Phase, TI has no
operations. A user also needs to perform two hash operations
and one asymmetric encryption operation, that is
ms. A SM needs to perform two hash operations, one
asymmetric encryption operation and two asymmetric
decryption operations, that is
ms.
EXPERIMENTAL CONFIGURATIONS
There is no computation operation in Tracing Phase.
TABLE IV presents the computation overhead of TI, a
user and a SM.
The experiment is implemented by using Go language
based on package bn256 [14] and golang elliptic library [15].
The hash function adopted in the experiment is SHA-256.
And the parameter settings in the scheme includes 32-bit
timestamp, 160-bit RID/DID/PDID, 128-bit random number.
Each relevant cryptographic operation is performed 1000
From the results in TABLE IV, we can get that our
proposed Metaverse-AKA scheme is lightweight. A user only
needs 1.459 ms to finish the cross-metaverse authentication
phase, which has better efficiency than 47.896 ms in scheme
of [6] and 9 ms in scheme [7].
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TABLE IV COMPUTATION OVERHEAD (MS)
Entity
Phase
Initialization Phase
Registration Phase
Avatar Creation Phase
User Login Phase
Mutual Authentication Phase
Cross-Metaverse
Authentication Phase
Total
ACKNOWLEDGMENT
TI
User
SM
0.698
0.103(N+2)
-
0.698
0.0015
0.0015
0.002
0.698
0.002
0.0025
-
1.459
2.917
0.103N+0.904
2.162
3.6195
This work was supported by Henan Key Laboratory of
Network Cryptography Technology under Grant LNCT2020A07 and National Key Research and Development Program
of China under Grant 2020YFB2103802.
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3) Communication Overhead
Firstly, there is no communication cost in Initialization
Phase, User Login Phase and Tracing Phase.
In Registration Phase, a user sends
-bit
message to TI and receives
-bit message
from TI. A SM sends 704-bit message to TI and receives
1024-bit message from TI.
In Avatar Creation Phase, a user sends 1440-bit message
to a SM and receives 768-bit message from the SM.
In Mutual Authentication Phase, a user sends 640-bit
message to a SM and receives 384-bit message from the SM.
In Cross-Metaverse Authentication Phase, a user sends
1216-bit message to SMs. And a SM sends 512-bit message
to another SM.
Therefore, the communication overhead in our scheme is
significantly smaller than 1,536 bytes in scheme of [6] and
288 bytes in scheme [7], which are not in an order of
magnitude.
To sum up, Metaverse-AKA scheme has better efficiency.
VI. CONCLUSION
This paper designs a lightweight and privacy-preserving
seamless cross-metaverse authentication and key agreement
scheme (Metaverse-AKA) for metaverse. Our proposed
Metaverse-AKA scheme can provide the seamless crossprivacy by achieving the anonymity and unlinkability. In
addition, Metaverse-AKA scheme also can trace the users of
the physical world with illegal behaviors in virtual world.
-AKA
scheme can resist multiple attacks like impersonation attack,
man-in-the-middle attack and replay attack. Finally, the
proposed scheme is lightweight by adopting lightweight
cryptographic primitives and conducting experiments to
evaluate the performance of our scheme.
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