Key Guidance Invocation: A White-box Mode Enables Strong Space Hardness under Adaptively Chosen-Space Attacks

The notion of space hardness serves as a quantitative measure to characterize the resilience of dedicated white-box schemes against code-lifting attacks, making it a widely utilized metric in the field. However, achieving strong space hardness (SSH) under the adaptively chosen-space attack model (ACSAM) remains an unresolved challenge, as no existing white-box scheme has given SSH guarantees under ACSAM. To address the problem, we introduce a novel mode of operation tailored for white-box cryptography, termed the Key Guidance Invocation (KGI) mode. Our security analysis reveals that the KGI mode not only significantly strengthens the resistance to adaptively chosen-space attacks, but also ensures SSH under ACSAM. Moreover, we propose a dedicated white-box construction, RubikStone, which directly leverages the concept of the lookup table pool.

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