IEEE Power Electronics Magazine - December 2021 - 70

White Hot
(continued from page 76)
( " snooping " ) of communications.
Aside from preventing an unauthorized
user from gaining access to a
communications channel encryption
is again the preferred way to prevent
unwanted listeners.
As mentioned above any power
electronics equipment connected to
the internet, such as renewable energy
inverters supplying power to the
grid, need world class cybersecurity.
But what about power supplies and
converters that are
not attached to the
internet? Like power
supplies in servers,
indust r ial equip -
ment, office equipment,
or even medical
equipment?
This question is
the communication with the power
supply is only to request status information,
such as output current, operating
temperature, or input power. If
the interface does not allow for an
external agent to change the operation
of the power supply, such as
turning it off, then there may be no
need for something like password
enabled access.
Even with these arguments there
motivated by discussions
the PMBus
Specification Working
Group is having
about adding security to the PMBus
protocol. But there are many power
converters with digital interfaces
that do not use the PMBus protocol
but interfaces based on I2C or even
basic serial buses. There is equipment
with power supplies whose
operation can be controlled from a
front panel user interface using keyboards,
keypads, or touch screens.
How much cybersecurity do these
power supplies need?
It is a fair question to ask if these
power supplies need any security
measures at all. Power supplies with
digital interfaces that are embedded
in other equipment are generally controlled
by some system level controller.
It is reasonable to argue that the
burden of preventing cyber attacks
lies with the system controller and
not the power supply. This leads to
the concept of layered security. After
all, if a malicious party gains control
of the system controller then the system
has big problems not related to
the power supply.
Another case where the need for
security can be questioned is when
Any power electronics
equipment connected
to the internet, such as
renewable energy
inverters supplying
power to the grid,
need world class
cybersecurity.
is still a push to add digital security
to embedded power
supplies. One reason
is that a malicious
actor that has control
of a power supply
can destroy a system
by setting an output
voltage too high. There
is also the issue of
being able to update
the firmware in a
power supply. In this
case the power supply
receiving the updated firmware
must be able to know that the update
is coming from an authorized source
and that it has not been tampered
with while in transit. That requires
robust security including authentication
and validation.
An argument against adding digital
security to power supplies is
the cost and complexity. System
OEMs already demand the lowest
possible price for any power supply
or converter. Simply adding the
capability for encrypted passwords
would add notable cost-notable
being in the range of US$0.50-1.00.
However, this cost is being accepted
by some system OEMs. There
are mobi le phone chargers that
have ARM based processors for
security and authentication of the
attached device.
One issue with adding password
protection is how the password gets
set and changed. Even if the power
supply manufacturer embeds a password
then there is the challenge
of keeping that password secure
throughout the system manufactur70
IEEE POWER ELECTRONICS MAGAZINE z December 2021
ing process and later when the system
is put into operation.
There is also the question of two
factor authentication. This will be
essentially impossible for most
embedded power supplies as there is
not a second, independent channel of
communication for the second factor.
So password protection will need to
rely on single secure passwords.
Communication overhead is also
an issue with providing digital security
for embedded power supplies. In
the PMBus protocol most commands
are only two bytes and the entire
packet, including a one byte checksum,
is four bytes. If a strong password
is needed general ly that
requires at least 128 bits (16 bytes) or
even 256 bits (32 bytes). To transmit
these additional bytes greatly slows
the bus and reduces the communication
efficiency.
Another issue is time. Some commands
to a power supply, such as
" Turn off now! " must be executed as
fast as possible. Adding digital security
requires the time to decrypt the
message and then the time to
authenticate the password. No matter
how much processing power is
put into the power supply this will
take a significant amount of time
making near-real time control essentially
impossible.
An interesting case is equipment
where the power supply is controlled
by a user interface such as a keypad
or touchpad. Given that there is a person
in physical contact with the
equipment, how much security is
needed? In general, the need for security
is going to be determined by the
nature of and application of the
equipment and will be governed by
the security needs of the overall
system. One example would be electro-surgical
equipment where the
equipment settings need to be made
only by properly trained and authorized
personnel (e.g. the surgeon).
I have asked a lot of questions and
presented different pros and cons for
digital security for embedded power
IEEE Power Electronics Magazine - December 2021

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