Modulation and Side Channels

Question 1

Other classification of EM emissions

Answer 1

direct emanations and unintentionally modulated emanations

Question 2

what are direct emanations and what are some properties associated with them?

Answer 2

• Result of direct current flows from within IC
• Observable over wide frequency band
• Higher frequencies are better because they have less noise
• Need to be close to the source

Question 3

what are unintentionally modulated emanations?

Answer 3

they are the result of carrier signals produced by IC (ex clock signal)

Question 4

AM

Answer 4

Amplitude modulation - change amplitude of signal to relay message (carrier + data signal)

Question 5

FM

Answer 5

Angle/Phase Modulation - change in frequency of signal to relay message

Question 6

Phase modulation

Answer 6

• Two carrier signals, same signal, just shifted by pi

- Embed a digital (0/1) signal - when we want to transmit a 0, use first carrier signal, use second signal for 1

Question 7

how are pulse modulations different from continuous wave modulations?

Answer 7

PM use square pulse carrier, continuous use sinusoid

Question 8

PAM

Answer 8

Pulse amplitude modulation - Amplitude of message is multiplied by the pulse signal

Question 9

PWM

Answer 9

Pulse width modulation - Different width of the pulse represents different message signal

Question 10

PPM

Answer 10

pulse position modulation - Amplitude and width remain the same, but modify the position of the pulse within the sampling period

Question 11

square pulse signal examples

Answer 11

• Processor clock
• Memory clock
• Voltage regulator
• Power supply
• Memory refresh

Question 12

what causes digital side channels?

Answer 12

square pulse signal is modulated with program activity

Question 13

digital side channels have what types of modulations (incl example)

Answer 13

PWM - Difference instructions lasts different amounts of time per clock cycle
PAM - Different instructions consume different amounts of energy

Question 14

analog vs digital

Answer 14

analog is continuous wave (sinusoid), digital is clock

Question 15

screaming side channels. what are they? how are they created?

Answer 15

digital signal gets modulated onto an analog signal via connection through ground or voltage supply plane

Question 16

SAVAT

Answer 16

Signal Available to Attacker - qualifies instruction-level differences available to the attacker

Question 17

How does SAVAT compare instructions?

Answer 17

Measure (A/B) and compare the two by integrating over the peak to get total power and then divide by number of (A/B) instances => get the energy/instruction

Question 18

What is an advantage of SAVAT?

Answer 18

Can measure at any frequency

Question 19

What are the loudest / weakest instructions according to SAVAT?

Answer 19

loudest = load/store to memory, divide
weakest = add/sub

Question 20

What are the loudest / weakest instructions according to SAVAT?

Answer 20

loudest = load/store to memory, divide
weakest = add/sub

Question 21

How to use SC to get information about loops?

Answer 21

Each iteration of a loop will have its own signal/frequency, which will repeat over time

Question 22

Describe the frequency domain representation of a modulated signal (AM)

Answer 22

• Middle peak for carrier signal

- Peaks on either side for message signal (carrier freq +- alternation freq)

Question 23

Steps for spectrum profiling

Answer 23

train with instrumentation
train without instrumentation
profile spectrogram

Question 24

cons of instrumentation

Answer 24

• Changes behavior of program
• Limited support
• Might need to analyze already-deployed devices

Question 25

what is spectrum profiling?

Answer 25

Spectral profile measures the loops in the program by monitoring EM emanations in frequency

Question 26

how to eliminate noise in spectrogram

Answer 26

by running spectrogram before/after program is run to find the noise