Aerospace and Electronic Systems - October 2018 - 26

A Survey on Securing UAS Cyber Physical Systems
higher level by experts in the field, however, conventional cyber
techniques need to evolve from the paradigm of build it, then secure it, to a more concurrent design approach. It is necessary to
not only assess the UAS from a high-level system view, but also
from a low-level hardware perspective using a more detailed holistic approach. The objective of a cyberattack on a UAS can be
categorized as one of two types: mission envelope failure or flight
envelope failure. Mission envelope failure is defined as restrictions
placed on the vehicle by a cyberattack (i.e. altitude limits, GPS
boundaries, etc.) that result in failure to successfully complete the
UASs mission. Flight envelope failure refers to a failure of the
flight control system to maintain the vehicle's state within the acceptable operating envelope, resulting in failure of the vehicle's
air-frame and often vehicle destruction.
These components can be further categorized into four main
categories: network, firmware, sensor, and GCS. The first, network
attacks, can include any type of wired or wireless communications
attack. Second are firmware attacks, which are related to the exploits on the software/firmware executing of the main processor of
the system. Third are the sensor attacks, which refer to actions affecting the firmware on the physical sensor, external reference manipulation, and any manipulation of an on-board component such
as the actuators. Last are the GCS attacks which are performed on
the computer and/or software the operator uses to control and communicate with the UAS. The following sections will go into further
detail of hardware, wireless, sensor, and GCS attacks on a UAS.

NETWORK ATTACKS
UASs typically use wireless communications links for command,
communications, and control (C3). The C3 link allows a GCS operator to send navigational commands to change the vehicles flight
path, altitude, airspeed, etc. as well as receiving system status and
health information from the vehicle. The data communications link,
if applicable, allows the real-time transmission of data gathered by
the vehicle (e.g. video) to be sent to the operator or other entities.
Usually, the data communications link does not affect the operation
of the vehicle meaning that it is not safety-critical, although interrupting it may effectively cause a Mission Envelope Failure.
UASs were not historically designed with the consideration that
the wireless communication channel would be a vulnerability. It has
become evident, however, that the vulnerabilities in UAS communication links can be exploited. With UASs becoming more popular,
the use of new, low cost, small, lightweight, and fast encryption capabilities will reduce the probability of wireless security problems.
Techniques for securing the wireless communication link in UASs
are presented in [8], [9]. In addition, an assessment of different wireless communication channels and sensor attack analysis is performed
in [10]; In UAS communication, there are four basic communication
architectures [11]: direct link/ad hoc, satellite, cellular, and mesh
networking. Direct link refers to a connection that is reliable with
low latency and little to no interference, satellite communication improves coverage, however has limited bandwidth; cellular refers to
using downlink towers that can be extended for better coverage; and
a mesh architecture treats each node as a relay in the system.

Two types of wireless communication for UASs exist, line-ofsight (LOS) and indirect. Indirect communication typically refers
to satellite communication. The most common frequency bands
used for wireless communication in unmanned systems are 400
MHz, 900 MHz, 15.15 GHz-15.35 GHz, 4 GHz-8 GHz, 2.4 GHz,
and 5.8 GHz. The 400 MHz band is commonly used throughout
Europe and the rest of the world (excluding the U.S.); lower power
required, lower path loss than 900 MHz, translating to less power
for the same range. However, with the lower frequency channel
bandwidths can be limited to 10 kbits/s or less. The 900 MHz band
is commonly used for UASs for narrow band lower data rate applications than the 2.4 GHz 5.8 GHz band. The 900 MHz band
offers better performance than 2.4 GHz or higher bands when obstructions such as trees and water are present. It is often used in
non-LOS applications [12]. The 15.15 GHz-15.35 GHz up link
and 14.40-14.85 down link is referred to as the Tactical Common
Data Link Ku band; a secured link developed by the military and
that is susceptible to interference and can be affected by rain/snow
and air humidity. The 4 GHz-8 GHz range is referred to as the
C-band. The UAS range is typically 4.4 GHz-4.94 GHz and 5.25
GHz-5.75 GHz, which are less susceptible to air humidity, but
subject to interference by many commercial off the shelf (COTS)
devices. The most commonly used band is WiFi a/b/g/n: 2.4 GHz-
2.48 GHz and 5.15 GHz-5.75 GHz; which uses multiple-input and
multiple-output and up to four antennas; omnidirectional antenna
can be used, however, there is an increased risk of eavesdropping
due to its unlicensed commercial nature.
A UAS has three main security breaches associated with its
control and telemetry wireless data link [13]: packet forwarding,
eavesdropping, and hijacking. Packet forwarding is a technique
where the data packets are delivered in an irregular way such as
dropping, duplication, or modification of packets. Eavesdropping
refers to an adversary silently listening to the communication, and
hijacking is when an adversary gains control of the vehicle through
mimicking the GCS.
A typical UAS-GCS communication can be classified as a mobile ad hoc network (MANET) similar to a wireless sensor network
(WSN). A WSN typically has static nodes and a MANET consists
of dynamic nodes. They pose many of the same vulnerabilities,
however with a MANET certain attacks, such as proximity-based
attacks (i.e. jamming), would be less effective because the attacker
must be mobile. In order to understand how a UAS may be vulnerable to wireless attacks, WSNs vulnerabilities are investigated. The
major attacks on a wireless network can be categorized as follows:
C

Denial of Service (DoS):
Physical Layer: Jamming, tampering
Link Layer: Collision exhaustion, unfairness
Network Layer: Neglect and greed, homing, misdirection,
black holes
Transport Layer: Flooding, desynchronization

Attack on Information in Transit: Information may be
spoofed, replayed, or vanished.

IEEE A&E SYSTEMS MAGAZINE

OCTOBER 2018

Aerospace and Electronic Systems - October 2018

Table of Contents for the Digital Edition of Aerospace and Electronic Systems - October 2018