Substitute Box with Obfuscation Input for Side Channel Resistance
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Solution Overview
Problem
The SM4 hardware architecture is vulnerable to side channel attacks due to predictable power consumption when the input pattern remains unchanged, allowing attackers to easily correlate power consumption with the 128-bit input, thereby compromising the encryption key.
Innovation Solution
A substitute box and apparatus that incorporates obfuscation input data unrelated to plaintext, combined with target input data to generate randomized output data, breaking the correlation between power consumption and the encryption key through reversible and affine operations, and secret sharing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the SM4 hardware architecture uses a fixed structure for encryption, then the encryption process is efficient and simple, but the power consumption becomes predictable and vulnerable to side channel attacks
Solution Approach 1:
The patent applies dynamics by making the substitution box structure variable rather than fixed. The substitution table is dynamically selected based on the round number and key material, causing the substitution behavior to change throughout the encryption process. This dynamic behavior ensures that power consumption patterns do not repeat predictably, thereby resisting side channel attacks while maintaining encryption efficiency
Solution Approach 2:
The patent changes the substitution parameters (substitution tables) based on the round number and key material. Different substitution tables are used in different rounds and for different key values, which transforms the power consumption characteristics. This parameter change approach allows the system to maintain high encryption efficiency while eliminating the predictable power consumption patterns that make fixed structures vulnerable to side channel attacks
2Device complexity
If the same substitution box is used for all rounds, then the hardware architecture is simple, but the intermediate values remain identical for unchanged inputs making key extraction easy
Solution Approach 1:
The patent segments the single substitution box into multiple round-specific substitution boxes, where each round uses a different substitution table. This segmentation is achieved by dividing the substitution box into multiple instances (e.g., four 4x4 substitution boxes) and selecting different combinations for different rounds. This segmentation increases security by ensuring that intermediate values change even when inputs remain the same, while keeping hardware complexity manageable through efficient resource sharing and selection mechanisms
Solution Approach 2:
The patent implements multi-functionality by designing substitution boxes that can serve multiple purposes: they perform substitution operations for different rounds with different substitution tables, and they can be selectively activated based on the current round number. This universal design allows the same hardware structure to provide both simplicity and security by dynamically configuring which substitution table is used, rather than requiring completely separate hardware for each round
Data Source
AI summary
A substitute box includes a target input terminal, an obfuscation input terminal, a first output terminal and a second output terminal. The target input terminal is configured to receive a target input data. The obfuscation input terminal is configured to receive an obfuscation input data unrelated to a plaintext. The first output terminal is configured to output a first output data. The second output terminal is configured to output a second output data associated with the first output data. The first output data and the second output data are generated according to both the target input data and the obfuscation input data.