AES Key Schedule for DPA-Resistant Block Cipher Updates
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Solution Overview
Problem
Existing techniques for countering differential power analysis (DPA) attacks in block cipher algorithms are either computationally intensive or impractical, and methods like hash function-based key rolling are costly in processing time and system resources.
Innovation Solution
A method for updating encryption keys in a block cipher algorithm by generating and retaining round keys to derive subsequent block keys, using the AES algorithm to encrypt and decrypt data blocks, ensuring that the same key material is never reused, thereby thwarting DPA attacks without additional processing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hash function-based key rolling is used to counter DPA attacks, then security against DPA attacks is improved, but processing time and system resources increase
Solution Approach 1:
The patent extracts the key rolling functionality from the hash function and integrates it directly into the AES key schedule algorithm. By taking out the external hash function dependency and embedding key update logic within the existing AES key expansion, the solution eliminates the computational overhead of separate hash operations while maintaining security against DPA attacks through continuous key material updates.
Solution Approach 2:
The patent merges the key rolling mechanism with the AES key schedule by combining the key update operations into a unified process. The same cryptographic operations that generate round keys for AES encryption are simultaneously used to derive updated block keys, eliminating redundant computations and reducing processing time while ensuring that hash function-based key rolling is replaced with an integrated approach.
2Reliability
If hash function-based key rolling is used to counter DPA attacks, then security against DPA attacks is improved, but system resources and device circuitry increase
Solution Approach 1:
The patent makes the AES key schedule algorithm multi-functional by enabling it to perform both its traditional role of generating round keys and the additional function of generating updated block keys for subsequent encryption operations. This universal approach eliminates the need for separate hash function circuitry and associated system resources, as the same cryptographic engine serves multiple purposes.
Solution Approach 2:
The AES key schedule algorithm serves itself by generating all necessary key material internally without requiring external hash function support. The key expansion process automatically produces both round keys for current encryption and updated block keys for future operations, making the system self-sufficient and reducing overall device complexity by eliminating external dependencies.
3Reliability
If key rolling techniques are used to counter DPA attacks, then security against DPA attacks is improved, but computational intensity increases
Solution Approach 1:
The patent segments the key generation process into two integrated components: round key generation for current encryption rounds and block key generation for subsequent operations. Both segments utilize the same AES key schedule operations, dividing the computational workload efficiently without requiring separate intensive hash function computations, thereby maintaining security while managing computational intensity.
Data Source
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AI summary
A method herein is for encryption key update in a station. In the method, a first data block is encrypted using a first plurality of round keys over a first plurality of rounds to generate a first encrypted data block, wherein the first plurality of round keys are generated based on an initial block key. A round key of the first plurality of round keys is retained for use as a basis for a first derived block key. A second data block is encrypted using a second plurality of round keys over a second plurality of rounds to generate a second encrypted data block, wherein the second plurality of round keys are generated based on the first derived block key. A round key of the second plurality of round keys may be retained for use as a basis for a second derived block key.