不调用库用matlab写一段DES代码

以下是一个简单的 MATLAB 实现 DES 加密算法的代码：

function ciphertext = des(plaintext, key, mode)
% DES 加密算法实现
% plaintext: 明文，必须为 8 个字节的 ASCII 字符串
% key: 密钥，必须为 8 个字节的 ASCII 字符串
% mode: 加密模式，可以选择 ECB 或 CBC
% ciphertext: 密文，与明文具有相同的长度和格式

% 检查输入参数
if nargin < 3
    mode = 'ECB';
end
if nargin < 2
    error('Missing key argument');
end
if nargin < 1
    error('Missing plaintext argument');
end
if length(plaintext) ~= 8
    error('Plaintext must be 8 bytes long');
end
if length(key) ~= 8
    error('Key must be 8 bytes long');
end

% 生成子密钥
subkeys = gen_subkeys(key);

% 加密明文
if strcmp(mode, 'ECB')
    ciphertext = des_ecb(plaintext, subkeys);
elseif strcmp(mode, 'CBC')
    % 初始化向量 IV
    iv = randi([0, 255], 1, 8);
    ciphertext = des_cbc(plaintext, subkeys, iv);
else
    error('Invalid mode argument');
end
end

function ciphertext = des_ecb(plaintext, subkeys)
% DES ECB 加密算法实现
% plaintext: 明文，必须为 8 个字节的 ASCII 字符串
% subkeys: 16 个子密钥，每个子密钥为 48 位
% ciphertext: 密文，与明文具有相同的长度和格式

% 将明文转换为 64 位二进制序列
bits = ascii_to_bits(plaintext);

% 初始置换 IP
bits = permute_bits(bits, IP);

% 迭代 16 次 Feistel 网络
L = bits(1:32);
R = bits(33:64);
for i = 1:16
    L_new = R;
    R_new = L + f(R, subkeys{i});
    L = L_new;
    R = R_new;
end

% 合并 L 和 R
bits = [R; L];

% 结尾置换 IP^-1
bits = permute_bits(bits, IP_INV);

% 将二进制序列转换为密文
ciphertext = bits_to_ascii(bits);
end

function ciphertext = des_cbc(plaintext, subkeys, iv)
% DES CBC 加密算法实现
% plaintext: 明文，必须为 8 个字节的 ASCII 字符串
% subkeys: 16 个子密钥，每个子密钥为 48 位
% iv: 初始向量，必须为 8 个字节的随机字符串
% ciphertext: 密文，与明文具有相同的长度和格式

% 将明文转换为 64 位二进制序列
bits = ascii_to_bits(plaintext);

% 初始置换 IP
bits = permute_bits(bits, IP);

% 迭代 16 次 Feistel 网络
L = bits(1:32);
R = bits(33:64);
for i = 1:16
    L_new = R;
    R_new = L + f(R, subkeys{i});
    L = L_new;
    R = R_new;
end

% 合并 L 和 R
bits = [R; L];

% 结尾置换 IP^-1
bits = permute_bits(bits, IP_INV);

% CBC 模式异或前一个分组的密文
bits = bitxor(bits, iv);

% 将二进制序列转换为密文
ciphertext = bits_to_ascii(bits);
end

function subkeys = gen_subkeys(key)
% 生成 DES 子密钥
% key: 密钥，必须为 8 个字节的 ASCII 字符串
% subkeys: 16 个子密钥，每个子密钥为 48 位

% 将密钥转换为 64 位二进制序列
key_bits = ascii_to_bits(key);

% 初始置换 PC1
key_bits = permute_bits(key_bits, PC1);

% 迭代 16 次生成子密钥
C = key_bits(1:28);
D = key_bits(29:56);
subkeys = cell(1, 16);
for i = 1:16
    % 根据移位表循环左移 C 和 D
    C = circshift(C, [0, SHIFT[i]]);
    D = circshift(D, [0, SHIFT[i]]);
    % 合并 C 和 D
    CD = [C; D];
    % 压缩置换 PC2
    subkeys{i} = permute_bits(CD, PC2);
end
end

function bits = ascii_to_bits(ascii_str)
% 将 ASCII 字符串转换为 64 位二进制序列
bits = dec2bin(ascii_str, 8) - '0';
bits = reshape(bits', 1, []);
end

function ascii_str = bits_to_ascii(bits)
% 将 64 位二进制序列转换为 ASCII 字符串
bits = reshape(bits, 8, [])';
ascii_str = char(bin2dec(num2str(bits))');
end

function bits = permute_bits(bits, perm)
% 按照置换表 perm 对 64 位二进制序列进行置换
bits = bits(perm);
end

function output = f(R, subkey)
% Feistel 网络函数
% R: 32 位二进制序列
% subkey: 48 位子密钥
% output: 32 位二进制序列

% 扩展置换 E
bits = permute_bits(R, E);

% 与子密钥异或运算
bits = bitxor(bits, subkey);

% 分组代替置换 S1-S8
s_outputs = zeros(8, 4);
for i = 1:8
    s_input = bits((i-1)*6+1:i*6);
    row = bi2de([s_input(1), s_input(6)]);
    col = bi2de(s_input(2:5));
    s_outputs(i,:) = de2bi(S{i}(row+1, col+1), 4);
end
s_outputs = reshape(s_outputs', 1, []);

% 置换 P
output = permute_bits(s_outputs, P);
end

% 下面是置换表和常量定义

% 初始置换 IP
IP = [58, 50, 42, 34, 26, 18, 10, 2, ...
      60, 52, 44, 36, 28, 20, 12, 4, ...
      62, 54, 46, 38, 30, 22, 14, 6, ...
      64, 56, 48, 40, 32, 24, 16, 8, ...
      57, 49, 41, 33, 25, 17, 9, 1, ...
      59, 51, 43, 35, 27, 19, 11, 3, ...
      61, 53, 45, 37, 29, 21, 13, 5, ...
      63, 55, 47, 39, 31, 23, 15, 7];

% 结尾置换 IP^-1
IP_INV = [40, 8, 48, 16, 56, 24, 64, 32, ...
          39, 7, 47, 15, 55, 23, 63, 31, ...
          38, 6, 46, 14, 54, 22, 62, 30, ...
          37, 5, 45, 13, 53, 21, 61, 29, ...
          36, 4, 44, 12, 52, 20, 60, 28, ...
          35, 3, 43, 11, 51, 19, 59, 27, ...
          34, 2, 42, 10, 50, 18, 58, 26, ...
          33, 1, 41, 9, 49, 17, 57, 25];

% 扩展置换 E
E = [32, 1, 2, 3, 4, 5, 4, 5, ...
     6, 7, 8, 9, 8, 9, 10, 11, ...
     12, 13, 12, 13, 14, 15, 16, 17, ...
     16, 17, 18, 19, 20, 21, 20, 21, ...
     22, 23, 24, 25, 24, 25, 26, 27, ...
     28, 29, 28, 29, 30, 31, 32, 1];

% 置换 P
P = [16, 7, 20, 21, 29, 12, 28, 17, ...
     1, 15, 23, 26, 5, 18, 31, 10, ...
     2, 8, 24, 14, 32, 27, 3, 9, ...
     19, 13, 30, 6, 22, 11, 4, 25];

% 初始密钥置换 PC1
PC1 = [57, 49, 41, 33, 25, 17, 9, ...
       1, 58, 50, 42, 34, 26, 18, ...
       10, 2, 59, 51, 43, 35, 27, ...
       19, 11, 3, 60, 52, 44, 36, ...
       63, 55, 47, 39, 31, 23, 15, ...
       7, 62, 54, 46, 38, 30, 22, ...
       14, 6, 61, 53, 45, 37, 29, ...
       21, 13, 5, 28, 20, 12, 4];

% 压缩置换 PC2
PC2 = [14, 17, 11, 24, 1, 5, 3, 28, ...
       15, 6, 21, 10, 23, 19, 12, 4, ...
       26, 8, 16, 7, 27, 20, 13, 2, ...
       41, 52, 31, 37, 47, 55, 30, 40, ...
       51, 45, 33, 48, 44, 49, 39, 56, ...
       34, 53, 46, 42, 50, 36, 29, 32];
   
% S 盒
S{1} = [14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7; ...
        0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8; ...
        4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0; ...
        15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13];
S{2} = [15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10; ...
        3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5; ...
        0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15; ...
        13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9];
S{3} = [10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8; ...
        13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1; ...
        13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7; ...
        1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12];
S{4} = [7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15; ...
        13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9; ...
        10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4; ...
        3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14];
S{5} = [2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9; ...
        14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6; ...
        4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14; ...
        11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3];
S{6} = [12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11; ...
        10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8; ...
        9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6; ...
        4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13];
S{7} = [4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1; ...
        13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6; ...
        1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2; ...
        6, 11, 13, 8, 1, 4, 10, 7