1) As far as I know, Northeastern University in China is very strong in the field of information security. Many Japanese professors know that Northeastern University graduates are very capable, so don't sell yourself short, hehe;

2) Kyushu University, tokyo institute of technology, Tohoku University and Nagoya University also have strong professors in this field. This major still has a great choice in Japanese national universities (hundreds of related professors can be found through search engines);

3) Japanese national universities can apply for "graduate students" (similar to pre-master's degree) or "monks" for undergraduate graduates, but monks generally need to take exams in Japan, mainly specialized courses and English TOEFL (Japanese requires that the applicant's Japanese level can be evaluated through research plan, written test and interview, so it is generally not required to submit Japanese level), but apply for "graduate students" because there are generally no exams and interviews.

Postgraduate courses in Japanese national universities, similar to research postgraduate courses, need to have their own research direction and research content, so if you decide to study in Japan, it is also important to read some academic papers or related academic books in advance and determine your own research direction.

I wish you success in your studies.