Key Derivation Function Using XOR and AND Operations
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Solution Overview
Problem
Security microprocessors face vulnerabilities in maintaining the confidentiality of cryptographic keys due to side-channel attacks, which can determine the key value by observing auxiliary channels like power consumption and electromagnetic radiation, even with existing protective measures.
Innovation Solution
A method for generating derived cryptographic keys using a key derivation function that combines random and complementary operations with a symmetric block cipher algorithm, specifically F(K,X,S) = F(K,X,T) ⊕ F(K,X,∼T), where T is randomly chosen from S or its complement, to produce a key that is independent of the choice duration and resistant to side-channel attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a master key is used for multiple cryptographic operations, then productivity is improved, but reliability deteriorates due to increased vulnerability to side-channel attacks
Solution Approach 1:
The patent segments the key derivation process into multiple independent cryptographic operations (first encryption operation with first operand, second encryption operation with second operand). Each operation is isolated and contributes to the final derived key, preventing side-channel attacks from compromising the entire key through a single operation.
Solution Approach 2:
The patent introduces random operands as intermediaries in the key derivation process. These random values are combined with the master key through cryptographic operations to produce derived keys, acting as mediators that prevent direct observation of the master key through side-channel attacks while maintaining derivation efficiency.
2Reliability
If protective measures against side-channel attacks are implemented, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent changes the parameters of the cryptographic operations by varying the operands (first operand, second operand) in different derivation operations. This parameter variation ensures that each operation has a unique execution profile, making side-channel analysis ineffective while using the same underlying cryptographic algorithm, thus avoiding increased device complexity.
3Ease of operation
If the same cryptographic algorithm is used for key derivation, then ease of operation is improved, but reliability deteriorates due to predictable operation patterns
Solution Approach 1:
The patent introduces dynamic elements into the key derivation process by using random operands that change with each derivation operation. While the underlying cryptographic algorithm remains consistent (maintaining ease of operation), the actual operations become dynamic and unpredictable, preventing attackers from using predictable patterns in side-channel analysis.
Data Source
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AI summary
The method involves determining a derivation key function (KDF) from a permanent main key (K), a variable parameter (X) and a public or private key (S), where the key function comprises a cryptographic function controlled by the main key. A commutative operation is performed on two operands, where the operation comprises an exclusive OR operation and an AND operation. The derivation key function is calculated by selecting the variable parameter, calculating two keys using a cryptographic calculation unit of a safety microprocessor and combining the keys to produce a derived key (K').