1. Introduction | 简介
Simplified DES (SDES) is a simplified version of the Data Encryption Standard (DES), designed to help understand the DES encryption mechanism. While SDES is not cryptographically secure, it provides a foundation for understanding symmetric-key encryption.
简化数据加密标准（SDES）是数据加密标准（DES）的简化版本，旨在帮助理解 DES 加密机制。虽然 SDES 在密码学上并不安全，但它提供了理解对称密钥加密的基础。
2. Key Generation | 密钥生成
In SDES, a 10-bit key is used to generate two subkeys (K1 and K2). The key generation process involves three main steps:
在 SDES 中，使用 10 位密钥生成两个子密钥（K1 和 K2）。密钥生成过程包括以下三个主要步骤：
Permutation P10 (Given value)
置换 P10（给定值）
Permutation P8 (Given value)
置换 P8（给定值）
For example, given a key 1100011110, we obtain the following:
例如，给定密钥 1100011110，计算过程如下：
(注意：这里k1的shift是分开的左右两部分各自左移动一个位置。比如：P10(K): 00110 01111，则ShiftP10(K): 01100 11110。k2则是左移动三个位置）
Thus, we obtain K1 = 11101001 and K2 = 10100111.
因此，我们得到了 K1 = 11101001 和 K2 = 10100111。
3. S-Boxes (Given values) | S-盒（给定值）
S-Boxes are used for substitution in the SDES algorithm. SDES has two S-Boxes: S0 and S1.
S-Box 用于 SDES 算法中的替换操作。SDES 具有两个 S-盒：S0 和 S1。
4. Initial and Final Permutation | 初始和最终排列
The plaintext undergoes an initial permutation when it enters the encryption function, IP. It undergoes a reverse final permutation at the end IP−1 .
明文在进入加密函数IP时进行初始排列。最终在IP−1的末端进行反向排列。
IP (给定值)
IP-1 (给定值)
Applied to the input, we have the following after the initial permutation（The plaintext value is set to
0010 1000）:
5. Functions fk, SW, K | 计算fk, SW, K
• The function fk is defined as follows. Let P = (L, R), then fk(L, R) = (L ⊕ F (R, SK), R).
• The function SW just switches the two halves of the plaintext, so SW(L, R) → (R, L)
• The function F (p, k) takes a four bit string p and eight bit key k and produces a four bit output. It performs the following steps.
E/P (给定值)
Permutation P4 (Given value)
置换 P4（给定值）
The steps are:
（注意：看SBoxes是有规律的，同样也是分开左右两部分，左边的看S0，右边的看S1。并且对应的是中间看列，两边看行。比如：1111 1101，左边的为1111，取中间的“11”为列，取两边的“11”为行，看S0，得到10。右边的为1101，取中间的“10”为列，取两边的“11”为行，看S1，得到00。）
The result from F is therefore 0001
Calculating we then have fk1(L, R) = (0010 ⊕ 0001, 0010) = (0011, 0010) （这个0010 ⊕ 0001的0010是左半部分的值）
So far, then L = 0011 and R = 0010. SW just swaps them so R = 0011 and L = 0010.
We now do the calculation of fk2(L, R) = f{1010 0111}(0010 0011) = (0010⊕F (0011, {1010 0111}, 0011))
The steps for F are as above:
So now we have the outcome of F as 0011
Calculating we then have fk2(L, R) = (0010 ⊕ 0011, 0011) = (0001, 0011)
Last, we perform the IP−1 permutation:
So the final result of the encryption is 1000 1010.