Software Created Covert Channels

Question 1

Three covert channel examples

Answer 1

• Can repeat instructions to create a Morse code signal
• Repeat specific instructions to enhance signal strength (e.g. put a loop around key pressed to make the signal more obvious)
• Modify hardware to put system in different power states depending on what is being executed

Question 2

What is a power state covert channel?

Answer 2

Processor can be put into a high or low state depending on whether it is idle or not. Can create a covert channel by alternating between the two states

Question 3

Cons of covert channels

Answer 3

• Other program activity can interrupt our channels (i.e. we are transmitting 0s and 1s, and then the OS schedules something else!)
• Other programs can also change power levels (i.e we put the processor in the idle state, but another program is still running and keeps it in the active state)

Question 4

What considerations do we need to take when modeling side channels?

Answer 4

Need to take into account more than just the pipeline (i.e. include speculation, cache miss, etc)

Question 5

estimation of capacity?

Answer 5

what?