| A Side-channel Assisted Lattice Attack on Cryptographic Schemes based on Number Theoretic Transform |
 郭 彦廷
（指導教員：高安 敦／数理情報第1研究室）
CRYSTALS-Kyber is a key-encapsulation mechanism, whose security is based on the hardness of solving the learning-with-errors (LWE) problem over module lattices. As in its specification, Kyber prescribes the usage of the Number Theoretic Transform (NTT) for efficient polynomial multiplication. In this thesis, we present a two-step attack to achieve a full-key recovery on lattice-based cryptosystems that utilize NTT for efficient polynomial multiplication. First, we use CPA to recover a portion of the secret key from the power consumption of these polynomial multiplications in the decryption process. Then, using the information, we are able to fully recover the secret key by constructing an LWE problem with a smaller lattice rank and solving it with lattice reduction algorithms.
This study has provided me with valuable insights into the process of conducting thorough research. I want to express my sincere appreciation to my mentor, Lecturer Atsushi Takayasu, for guiding me through every phase of thesis writing and dedicating substantial time to provide instructive advice and valuable suggestions.
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