Aerospace and Electronic Systems - August 2019 - 35

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upsets (SEU) [14]. Hardware-defined (digital logic) and
software-defined (dedicated processors) approaches may
be used in satellites for encryption [14], and the choice of
encryption scheme depends upon the following factors.

The satellite may not have the required hardware/
software (HW/SW) for a chosen encryption scheme
and the scheme may degrade the efficiency and
capability of the satellite to handle messages.

Choice of encryption scheme affects the extent of signal degradation, leading to errors or gaps in the signal.
As a result, error detection (using checksums or hashing functions) and correction (EDAC) schemes are
applied to prevent irreversible data loss. However,
this increases overhead in the telemetry frame.

The extent of cryptographic applications depends
on the source, volume, and value of data, well
balanced with the satellite's HW/SW capabilities.
Transponders do not need encryption, as they
simply relay encrypted signals from other
satellites, whereas military telemetry and telecommand must be encrypted. However, new
policies dictate that the civilian satellites
should also have encrypted telecommand as discussed in "TRENDS IN SMALL SATELLITE
CYBERSECURITY".

The encryption scheme must be able to identify the
authenticity of the sender, which can be achieved
using "keyed encryption" schemes. Often, different
parties may want to access the satellite, wherein
asymmetric ciphers with distinct private keys and a
unified public key is used. However, such an
approach is slow and prone to eavesdropping.

Figure 1.
Security threats in electronic, cyber, and physical space on small
satellites systems, mapped to required onboard security services
to address the exploits [2], [4].

AUGUST 2019

It maybe counter-intuitive to protect the telemetry
channel besides the telecommand channel, but unencrypted telemetry poses several problems. If a hacker
injects malicious commands into the satellite by duplicating an encrypted telecommand channel and the telemetry channel is unencrypted, the hacker will be able to
receive confirmation if he has been successful and carry
forward more severe malicious attacks. Probable results
of such attacks have been described in "TRENDS IN
SMALL SATELLITE CYBERSECURITY" in brief. It
is possible to extract location data out of a satellite's
telemetry. Examples include unencrypted Iridium telemetry link and GPS/GLObal NAvigation Satellite System
(GLONASS) links [15]. Using the location data, malicious actors can identify location of interests to cause
peril. Spoofing location data can also help malicious
actors hijack vehicles, drones, and vessels [16]. It is possible to jam the telemetry channel if the telemetry channel is unencrypted, causing loss of information [17].
Hackers could use unencrypted metadata carried in the
telemetry channel to steal data from the infected
machines using hijacked satellite IP addresses of genuine
users [15].

IEEE A&E SYSTEMS MAGAZINE

Aerospace and Electronic Systems - August 2019

Table of Contents for the Digital Edition of Aerospace and Electronic Systems - August 2019