des算法的实现c++

DES（Data Encryption Standard）是一种对称加密算法，下面是一个简单的DES算法的实现（只用于学习和了解，不适用于实际加密）：

#include <iostream>
#include <bitset>
#include <cstring>

using namespace std;

// 初始置换表
const int IP[64] = {
    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
};

// 逆初始置换表
const int IP_INV[64] = {
    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
};

// 扩展置换表
const int E[48] = {
    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
};

// S盒
const int S_BOX[8][4][16] = {
    {
        {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}
    },
    {
        {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}
    },
    {
        {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}
    },
    {
        {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}
    },
    {
        {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}
    },
    {
        {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}
    },
    {
        {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, 9, 5, 0, 15, 14, 2, 3, 12}
    },
    {
        {13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7},
        {1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2},
        {7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8},
        {2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11}
    }
};

// P盒
const int P[32] = {
    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
};

// 密钥置换表
const int KEY_PC1[56] = {
    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
};

// 子密钥置换表
const int KEY_PC2[48] = {
    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
};

// 循环左移位数表
const int KEY_SHIFT[16] = {
    1, 1, 2, 2,
    2, 2, 2, 2,
    1, 2, 2, 2,
    2, 2, 2, 1
};

// 将64位明文/密文分为左右两部分（各32位）
void split(string msg, bitset<32>& left, bitset<32>& right) {
    for (int i = 0; i < 32; i++) {
        left[i] = msg[i];
        right[i] = msg[i + 32];
    }
}

// 将左右两部分合并为64位明文/密文
string merge(bitset<32> left, bitset<32> right) {
    string res;
    for (int i = 0; i < 32; i++) {
        res += left[i] ? '1' : '0';
    }
    for (int i = 0; i < 32; i++) {
        res += right[i] ? '1' : '0';
    }
    return res;
}

// 初始置换
void IP_transform(string& msg) {
    string res(64, '0');
    for (int i = 0; i < 64; i++) {
        res[i] = msg[IP[i] - 1];
    }
    msg = res;
}

// 逆初始置换
void IP_INV_transform(string& msg) {
    string res(64, '0');
    for (int i = 0; i < 64; i++) {
        res[i] = msg[IP_INV[i] - 1];
    }
    msg = res;
}

// 扩展置换
bitset<48> E_transform(bitset<32> right) {
    bitset<48> res;
    for (int i = 0; i < 48; i++) {
        res[47 - i] = right[32 - E[i]];
    }
    return res;
}

// S盒变换
bitset<32> S_transform(bitset<48> right) {
    bitset<32> res;
    for (int i = 0; i < 8; i++) {
        int row = right[47 - i * 6] * 2 + right[47 - i * 6 - 5];
        int col = right[47 - i * 6 - 1] * 8 + right[47 - i * 6 - 2] * 4 + right[47 - i * 6 - 3] * 2 + right[47 - i * 6 - 4];
        int num = S_BOX[i][row][col];
        for (int j = 3; j >= 0; j--) {
            res[31 - i * 4 - j] = num % 2;
            num /= 2;
        }
    }
    return res;
}

// P盒变换
bitset<32> P_transform(bitset<32> right) {
    bitset<32> res;
    for (int i = 0; i < 32; i++) {
        res[31 - i] = right[32 - P[i]];
    }
    return res;
}

// 生成子密钥
void generate_sub_key(string key, string sub_key[16]) {
    bitset<56> key_bitset;
    bitset<28> left, right;
    for (int i = 0; i < 56; i++) {
        key_bitset[55 - i] = key[KEY_PC1[i] - 1] == '1';
    }
    for (int i = 0; i < 28; i++) {
        left[27 - i] = key_bitset[55 - i];
        right[27 - i] = key_bitset[27 - i];
    }
    for (int i = 0; i < 16; i++) {
        left = ((left << KEY_SHIFT[i]) & 0xfffffff) | (left >> (28 - KEY_SHIFT[i]));
        right = ((right << KEY_SHIFT[i]) & 0xfffffff) | (right >> (28 - KEY_SHIFT[i]));
        bitset<56> merge_key(left.to_ulong());
        merge_key <<= 28;
        merge_key |= bitset<56>(right.to_ulong());
        for (int j = 0; j < 48; j++) {
            sub_key[i][j] = merge_key[55 - KEY_PC2[j]] ? '1' : '0';
        }
    }
}

// DES加密
string des_encrypt(string plaintext, string key) {
    string sub_key[16];
    generate_sub_key(key, sub_key);
    IP_transform(plaintext);
    bitset<32> left, right, new_left;
    split(plaintext, left, right);
    for (int i = 0; i < 16; i++) {
        new_left = right;
        right = P_transform(S_transform(E_transform(right) ^ bitset<48>(sub_key[i])));
        right ^= left;
        left = new_left;
    }
    string ciphertext = merge(right, left);
    IP_INV_transform(ciphertext);
    return ciphertext;
}

// DES解密
string des_decrypt(string ciphertext, string key) {
    string sub_key[16];
    generate_sub_key(key, sub_key);
    IP_transform(ciphertext);
    bitset<32> left, right, new_right;
    split(ciphertext, left, right);
    for (int i = 15; i >= 0; i--) {
        new_right = left;
        left = P_transform(S_transform(E_transform(left) ^ bit