Cryptographic Key Protection Against Unidirectional Attacks
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Solution Overview
Problem
Existing mechanisms for protecting cryptographic keys against unidirectional bit disturbances, such as laser attacks, are vulnerable to attacks that force bits into specific states, allowing attackers to determine the key's value, especially when multiple bits are targeted simultaneously.
Innovation Solution
A method involving non-deterministic selection of pairs of masks from a set of different masks, applying these masks to the key or message during encryption or decryption operations, and verifying consistency between multiple executions of the algorithm to detect integrity faults without making the key vulnerable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If integrity verification is performed by reading the key or performing two separate calculations, then the key integrity can be verified, but the key becomes vulnerable to unidirectional attacks where an attacker can force bits into specific states
Solution Approach 1:
The patent applies dynamics by randomly selecting different pairs of masks for each verification operation. This dynamic approach ensures that the verification process changes with each execution, preventing attackers from predicting or forcing specific bit states. The random mask selection makes the verification adaptive rather than static, thereby countering unidirectional attacks.
Solution Approach 2:
The patent changes the parameters of the verification process by using different mask pairs from a predefined set. Instead of using fixed masks, the system varies the mask parameters randomly for each verification, which alters the verification characteristics and prevents attackers from exploiting consistent patterns to force bit states.
2Reliability
If the key is reloaded frequently to counter modification during transfer, then transfer integrity is improved, but the key register remains susceptible to laser attacks
Solution Approach 1:
The patent introduces masks as intermediary elements between the key and the verification process. These masks act as mediators that obscure the key bits during verification, preventing direct observation or forcing of key bit states by laser attacks while still enabling integrity verification through the masked comparison process.
3Measurement precision
If direct reading or indirect verification is performed, then integrity can be checked, but the verification results can inform attackers about key bit values
Solution Approach 1:
The masks serve as intermediaries that prevent direct information leakage about key bit values. By comparing masked versions of the key rather than the key itself, the system maintains verification accuracy while preventing attackers from gaining information about the actual key bit states through the verification results.
Solution Approach 2:
The patent creates asymmetry between the verification process and the key storage. The verification operates on transformed (masked) data rather than the raw key, creating an asymmetric relationship where verification can detect errors without exposing the actual key values to attackers.
Data Source
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AI summary
The invention relates to a method of protecting a key (K) implemented, by an electronic circuit, in a symmetric algorithm (A) for encrypting or decrypting a message (T), comprising the steps of: selecting (71) in a non-deterministic way a pair of different masks (Mj, Mj') from a set of at least four different masks, the masks having the property of representing different combinations of bits, at least by bit pair; executing the algorithm twice (I, II) by applying, to the key or the message, one of the masks of the selected pair at each execution; and verifying (75, 76) the consistency between the two executions.