Despite their theoretical quantum attack resistance, practical implementations of post-quantum cryptography (PQC) algorithms remain susceptible to side-channel attacks. This includes all standard algorithms selected the National Institute of Standards and Technology (NIST) such as Kyber/ML-KEM, Dilithium/ML-DSA, Falcon/FN-DSA and SPHINCS+/SLH-DSA. This paper proposes an alternative defense for side-channel resilience based on 3D integration that uses 3D hardware to shield the underlying cryptographic activity by introducing decoy keys and physical shielding through stacking. The proposed approach can complement other security measures (such as masking and shuffling) on protecting Number Theoretic Transform (NTT) that move computation to dedicated NTT chips. We outline the construction of our approach and validate the effectiveness on a generic attack targeting intermediate computation inside an NTT butterfly.

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