Cryptography
1. Basis
\[
\begin{align}
\text{cipher} &= E_{\text{key}_e}(\text{msg})\\
\text{msg} &= D_{\text{key}_d}(\text{cipher}) \\
E_{\text{key}_e}( D_{\text{key}_d}(\text{msg}) ) &= \text{msg}
\end{align}
\]
1.1 Symmetric-key Algorithm
\(\text{key}_e = \text{key}_d\)
e.g. DES, RCx, AES
1.2 Public-key Cryptography (Asymmetric Cryptography)
\(\text{key}_e \ne \text{key}_d\)
e.g. RSA
1.3 Three Features
- Transportation or Substitution
- Number of keys (symmetric or asymmetric)
- Block or Stream cipher
1.4 Security
Unconditional secure
Computationally secure
2. Symmetric-key Algorithm
2.1 S-DES
2.2 Feistel
分组密码
偶数轮次
Last update:
September 30, 2021
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