Substitution-Permutation Cipher Masking Against Fault Injection

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Solution Overview

Problem

Cryptographic substitution-permutation networks are vulnerable to fault injection attacks, which can compromise secret data by interrupting computations and allowing attackers to decipher cryptographic keys due to incomplete or weak intermediate outputs.

Innovation Solution

Implement obfuscation transformations using invertible transforms based on random numbers during each round of computations in the substitution-permutation network, applying masking matrices and vectors to obfuscate intermediate outputs, ensuring that even incomplete computations produce cryptographically strong results.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If fault injection attacks interrupt cryptographic computations, then attackers can obtain intermediate outputs, but this reveals secret data and compromises security

Engineering Contradiction:

ImprovesecurityVSAvoidvulnerability to fault injection

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing obfuscation transformations on intermediate outputs before they can be exposed to attackers. Masking matrices and vectors are pre-computed and applied to encrypt intermediate results, ensuring that even if fault injection interrupts the computation, the exposed data remains protected. This proactive protection prevents the harmful effect of information leakage before it can occur.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If intermediate outputs are produced during cryptographic computations, then computation progress is visible, but this creates weak outputs vulnerable to cryptanalysis

Engineering Contradiction:

Improvecomputation speedVSAvoidcryptographic strength

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces masking matrices and vectors as intermediary elements between the cryptographic computation and the output. These intermediaries transform intermediate results into obfuscated forms that maintain computational efficiency while preventing direct access to meaningful cryptographic data. The masking acts as a mediator that preserves computation speed while eliminating the vulnerability of intermediate outputs.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If standard cryptographic operations are used without obfuscation, then implementation is simple, but secret data can be deciphered from interrupted computations

Engineering Contradiction:

Improveimplementation simplicityVSAvoidinformation leakage

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent changes the parameters of cryptographic operations by introducing obfuscation transformations with masking matrices and vectors. These parameter changes modify intermediate outputs without fundamentally altering the core cryptographic algorithm, maintaining implementation simplicity while adding a layer of protection. The transformed parameters ensure that even interrupted computations produce only obfuscated, non-sensitive data.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12500738B2Protection of cryptographic substitution-permutation networks from fault injection attacks

Publication Date: 2025.12.16 CRYPTOGRAPHY RESEARCH INC

AI summary

Aspects of the present disclosure involve a method and a system to perform the method to obtain a cryptographic output of a plurality of rounds of a cipher, by performing a plurality of modified rounds of the cipher, each of the modified rounds computing an unmasking transform, an operation of a respective round of the cipher, and a masking transform, the unmasking transform being an inverse of the masking transform of a previous round of the cipher.