1. Ali Galip Bayrak EPFL, Switzerland June 7th, 2011
A First Step Towards Automatic Application of Power Analysis Countermeasures
Ali Galip Bayrak
EPFL, Switzerland
June 7th, 2011
and
Francesco Regazzoni (UCL and Alari)
Philip Brisk (UC Riverside, USA)
François-Xavier Standaert (UCL, Belgium)
Paolo Ienne (EPFL, Switzerland)

2. Side-Channel Attacks Cryptographic Algorithm Plaintext Ciphertext
(e.g., “Encrypt me”)
Ciphertext
(e.g., “aB14t752s”)
Secret Key
(e.g., “I’m unknown”)
Leakage
(power consumption, EM radiation, timing etc.) 2

3. Power Analysis Attacks3

4. They are handled manually!!!
Motivation
PROBLEM:
They are handled manually!!! VS
ATTACK!
COUNTERMEASURE!
Software
Implementation
Analyze the algorithm
Determine the weaknesses
Apply the countermeasure
Protected
Implementation 4

5. Automatic Protection Flow5

6. Step I: Information Leakage Analysis
Normalized Mutual Information of Key and Leakage
Main point:
Determine the
leaking parts
of the software!

7. Step II: Transformation Target Identification
Local Modifications:
Protect each sensitive instruction
(peephole optimization).
Random Precharging (used here)
Global Modifications:
Protect all the nodes
between two sensitive nodes.
Masking
sbci r28,0xfd
ld r25,r28:r29
movw r18,r26
subi r18,0x4f
sbci r19,0xfd
movw r28,r18
ld r30,r28:r29
Main point: Determine the portions of the implementation
that need to be protected!

8. Step III: Code Transformation
sbci r28,0xfd
ld r25,r28:r29
movw r18,r26
subi r18,0x4f
sbci r19,0xfd
movw r28,r18
ld r30,r28:r29
sbci r28,0xfd
lds r25,rnd
mov r24,r25
ld r25,r28:r29 …
movw r18,r26
subi r18,0x4f …
Main point: Apply the given protection on the determined
portions of the implementation!

9. Experimental Results (Security)
Advanced Encryption Standard (AES) is used.
Traces are collected from board with 8-bit AVR MCU.
Correlation-based DPA attack is used for attack.
ρ = 0.437
ρ = 0.048
Correlation values for unprotected and protected implementations are shown.
Number of necessary traces to mount a successful attack
increases over 76 times. 9

10. Experimental Results (Performance)
# of clock cycles during the execution of three different implementations
4212
100%
2700
64%
1190 10

11. Conclusions Software Implementation Protected Implementation
AUTOMATIC
PROTECTION
Software
Implementation
Protected
Implementation
Off-the-Shelf
Compiler AP
Security-Aware Compiler
security vs. performance vs. energy etc. 11