IEEE Consumer Electronics Magazine - January/February 2024 - 80

Special Section on Security and Privacy-Aware Emerging Computing
an enormous scale, leading to a significant
shift in people's daily lives. Nowadays, academia
and industry are turning their attention to
emerging next-generation systems. It is envisioned
that the sixth-generation (6G) communications
will support five application scenarios:
Enhanced mobile broadband plus, big communications,
secure ultra-reliable low-latency
communications, three-dimensional integrated
communications, and unconventional data
communications.1 Space-air-ground integrated
networks (SAGINs) leverage the advantages of
satellite networks (including geosynchronous
Earth orbit (GEO) satellites, medium Earth
orbit (MEO) satellites, low Earth orbit (LEO)
satellites, and their mutual links), high altitude
platforms, and terrestrial communication systems.
SAGINs are therefore considered as a
promising architecture to support ubiquitous,
seamless, reliable, and high-data-rate services
anytime and anywhere in 6G communication
networks. Remarkably, practical experiments
and ambitious projects have been initiated to
offer ubiquitous Internet services through SAGINs,
such as Google Loon, Thales Stratobus,
OneWeb, and SpaceX.
SAGIN is a highly heterogeneous and multidimensional
network compared to conventional
terrestrial or satellite networks. It has wide coverage,
broadcast channels, and various network
entities, including networking infrastructure and
connected Internet of Thing (IoT) devices. However,
its wide coverage feature brings trust and
safety issues. Specifically, the wireless signal in
SAGIN propagates mainly in free space. In other
words, not only authorized users could receive
the information but also malicious users could
obtain wireless power and retrieve secure information
from power leakage in wireless signals.
Besides, intrinsic trust and data reliability issues
may arise in SAGIN during multihop transmissions
among distrustful entities within each segment
or across segments. Due to the lack of
unified security precautions, interconnected
intelligent devices can be vulnerable to various
cyber attacks, and traceable data provenance is
difficult.2 Therefore, merits including security,
privacy, and intelligence have become the crux
of determining whether SAGIN can continue to
evolve healthily.
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As the first security perimeter, authentication
is a pivotal method to identify the legitimacy
of IoT devices that access the network,
thereby enabling real-time monitoring and promoting
collaborative sharing.3,4 Authentication
can be classified into one-shot authentication
and continuous authentication based on the
duration of the authentication process. Oneshot
authentication is an elementary authentication
mechanism that identifies IoT devices
using crypto-based techniques such as passcodes,
PINs, and fingerprints. However, it only
protects the security of SAGIN during the initial
access process and cannot guarantee security
during the operational phase. With the proliferation
of intelligent IoT devices, especially wearable
devices like fitness bands and augmented
reality (AR) glasses, personal behavioral and
physiological biometrics can be easily collected
by built-in sensors, which promotes continuous
authentication from concept to
implementation. As an enhancement and supplement
to one-shot authentication, continuous
authentication defenses against attacks in the
background without user intervention by constantly
validating access devices according to
the historical features of users. To cope
with the new features of SAGINs, it becomes
increasingly essential to combine one-shot
authentication for quick access and continuous
authentication for sustainable security
together, supporting convenient access and
security robustness of various kinds of communication
entities.5
To adequately utilize the collected data
from IoT devices, adopting multifactor authentication
(MFA) is promising. This means that
multiple heterogeneous validation methods
can be combined intelligently to grant or deny
access reliably.6 In MFA, three types of factor
groups, i.e., knowledge factor, ownership factor
and biometric factor, are available to connect
an individual with the established
credentials. Knowledge factor, ownership factor,
and biometric factor refer to factors like
passwords, tokens, and behavioral patterns,
respectively. Specifically, spatial-temporal features,
such as geographical position, Doppler
shift and traffic volume, are likely to be utilized
in the continuous authentication phase due to
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IEEE Consumer Electronics Magazine - January/February 2024

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