Advanced Encryption Standard is most widely used encryption
algorithm in a symmetrical key cryptography. AES was standardized in 2001 after
3 year analysis for vulnerabilities. However the many cryptographic researchers
found vulnerabilities of the implementation of AES algorithm and one of the vulnerabilities
reported in literature is power analysis. Power analysis attacks exploit the
power consumption of the encryption process with the data being processed. Power
analysis attacks can be divided to many categories: 1) Simple power analysis;
2) differential power analysis.
Power consumption for logic 0 and logic 1 are clearly
distinguishable in the power trace when simple power analysis can be performed.
Some simple power analysis attacks involve analyzing one power trace. But often
more than one power trace is used in simple power analysis. Differential power analysis uses statistical
methods to identify the correlation between the power dissipation of the device
with the data being processed. Differential power analysis, Correlation power
analysis and Mutual information analysis are the example for well famous differential
power analysis attacks.
Power consumption of a device is the sum of the power
consumption of all logic gates. Total power dissipation of a logic gate is the
sum of the static and dynamic power consumption of the logic gate. Logic gates
are made from CMOS transistors. Explaining the detail of each logic gate is too
extensive and only basics are explained. Static power consumption depends on
the leakage current of the logic gate and the dynamic power consumption of the
logic gate, depends on the state transition of the logic gate. The table below shows the power consumption for different state transitions.
Traditional power analysis attacks exploit the dynamic power
dissipation of the device. That is by correlating the power consumption with
the dynamic power consumption, an adversary has the capability to deduce the
secret key. Often static power consumption is neglected when compared with
dynamic power analysis. When the transistor width is less than 90mn the static
power consumption plays a major role in the total power dissipation. Recently a
new exploitation in static power dissipation is announced by researchers, where
the static power consumption is taken into account. Power
analysis attacks are presented in both microprocessors as well as in circuits.
In order to thwart power analysis attacks, various countermeasures
have been proposed by cryptographic researchers. Masking the data being
processed, flatten the current drawn by the device and hide the dynamic power
using a compliment identical processing unit to obfuscate the power consumption
from the data being processed.
