IEEE Consumer Electronics Magazine - January/February 2024 - 84

Special Section on Security and Privacy-Aware Emerging Computing
minimal biases. Finally, through evaluations of a
verification system, the ultimate decision can be
made to grant access to legitimate users and
deny access to impostors. In this article, we envision
ATMAS to address challenges for the SAGIN.
The advantages of ATMAS are summarized as
follows.
Continuous Security. The proposed ATMAS
not only authenticates at the initial stage of login
but also provides seamless protection to legitimate
devices in the background by adopting AIenhanced
algorithms.
High Flexibility. We utilize a conventional
cryptographic authentication named " Phase I "
to quickly grant or deny service requester
access, and an AI-aided continuous authentication
named " Phase II " to intelligently verify legitimacy
during service operation. The SAGIN
system operator is flexible in choosing whether
to use only " Phase I " or to select a suitable number
of authentication factors based on security
requirements.
High Robustness. By utilizing multiple factors
in the procedure of continuous authentication,
it becomes difficult for adversaries to
imitate or crack all selected features in a single
round of communication based on received signals
and observations.
DESIGN OF THE PROPOSED ATMAS
IN SAGINS
Before introducing the detailed design of the
proposed ATMAS, we would like to provide an
overview of the architecture of the SAGIN, as
illustrated in Figures 1 and 2. The SAGIN system
consists of three segments: the user/device segment,
the ground/air/space access segment, and
the authentication segment. The user/device
segment is an assemblage of various end mobile
users and IoT devices, and it is assumed that
users and devices have the ability to sense their
locations, traffic, and biometrics. The ground/
air/space access segment consists of all kinds of
access entities, such as terrestrial BSs, high-altitude
platforms, and satellites. The authentication
segment is responsible for one-shot
authentication and continuous authentication.
In this article, the focus is on MEO/LEO satellites,
which have relatively shorter transmission
84
delays compared to the GEO satellites. This
allows satellites to provide large-scale coverage,
and beams of BSs or other relays ensure highprecision
user targeting.13 The authentication
procedure of the proposed ATMAS is shown in
Figure 3, in which four network entities are
involved: MU, BS, satellite, and NCC. In the following
sections, the authentication procedure
will be discussed in detail.
Phase I: One-Shot Authentication
We divide authentication of Phase I into three
procedures: initialization and enrollment, registration,
and one-shot authentication.
Initialization and Enrollment: The authentication
in Phase I is cryptography based. NCC
uses Elgamal encryption technology14 to generate
a private key and a corresponding public
key. The private key is stored by the NCC locally,
and the public key and its related key parameters
are published to other entities in SAGINs.
Based on the key parameters, other entities can
generate their own private keys and public keys,
respectively.
Registration: Before participating in the
authentication procedure, entities including
MUs, BSs, and satellites must register with the
NCC. The BS and the satellite have a similar registration
procedure and we take satellite registration
as an example. After receiving a
registration request from a satellite, the NCC
generates both a unique identity and a temporary
identity for the satellite. Authentication
parameters, such as satellite identities and
shared public keys, are stored locally on the satellite.
Next, the satellite generates a timestamp
and sends it, along with authentication parameters,
to the NCC. Upon receiving this information,
the NCC first verifies whether the
transmission delay (i.e., the difference between
the current time and the sent timestamp) is less
than the predefined delay threshold. If the transmission
delay does not meet the requirement,
the NCC rejects the registration request. Otherwise,
the NCC checks where the authentication
parameters sent by the satellite coincide with
parameters stored in the NCC's local database. If
the parameters do not match, the satellite registration
request is rejected. Otherwise, another
timestamp is generated and sent together with
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