Standard is the first formal standard for computer system

It divides the security of the computer system into 4 levels and 7 levels: low high class D security level, class C security level, class B security level, class a security level d1c1c2b1b2b3a152 data security and confidentiality the cryptosystem today is based on three basic hypotheses, namely, randomness hypothesis, Computational Hypothesis and physical hypothesis.