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258 || AWSAR Awarded Popular Science Stories - 2019
for 3 states (00,01,11), the number of toggles in the gate is at most 1 while for state=11 the number of toggles is 3 ( both inputs toggle and output also toggles). Each toggle in a digital device consumes energy and hence, the AND gate would consume more power when it is at state 11 than the other three states. Thus the power consumed by the gate would reveal information about the input states. This leakage of information is known as the power side-channel.
From the above example, we could infer two interesting points:
1. The difference in the number of toggles, also known as switching activity, could be used as a reliable indicator of the device’s resilience against power side-channel attacks. For example, a device which consumed uniform power across all input states would not leak any information via the power side-channel. This leads us to our second inference.
2. If it were somehow possible to ensure that the energy consumed by the AND gate when it toggles to state 11 was the same as the other three states then we could say that the device would not leak any information about the input states.
Thus, the problem of securing a digital device against power side channels can now be stated as,
all of them to adhere to a single fixed standard is nearly impossible to achieve. Another simple solution would be to introduce a power regulator which will normalize the power consumption of the device. But it is critical to examine this solution in the context of our mobile phones which have a strict area constraint. Today, we want our phones to be as small as possible. Introducing additional hardware would mean that additional gates have to be added which would in turn increase the overall area of the device. Thus, the question of securing digital devices can now be rephrased as:
“Is it possible to somehow ensure that the logic gates that consume different power at different input states now consume uniform power across all input states,‘without increasing the overheads’?”
In our research, we tackle this question by using the Mahabharata as an inspiration. In the Mahabharata, Kunti the mother of Pandavas prayed to the Sun God for a warrior. The Sun God, Surya, presented her with Karna, a boy who was born with a shield around him. Surya guaranteed Kunti that as long as Karna wore his shield he would remain invincible.
This inspired us to look for solutions that could be implemented at the manufacturing stages. Any solution implemented at the manufacturing stage would not only ensure that the device would meet the side-channel requirements but keep the overheads low since the designer or the manufacturer is now aware of the changes being implemented and has the flexibility to implement the change at whatever granularity right from changing an entire module to changing only a single gate in the entire design.
Our proposed solution titled Karna, enables the design manufacturer to identify regions in the design where the gates could potentially leak information via the power
“Is it possible to somehow ensure that the logic
gates that consume different power at different input states now consume uniform power across all input states?”
Karna: Side-channel aware design flow
The above question, can be tackled in various ways. One solution would be to design efficient logic which would only consume uniform power. Today, a simple phone is made up of hundreds to thousands of components each designed by tens of engineers. Expecting