不使用任何库，用C++写出AES加密算法

AES（Advanced Encryption Standard）是一种对称加密算法，它使用相同的密钥用于加密和解密数据。下面是一个简单的C++实现AES加密算法的示例代码。

#include <iostream>
#include <cstring>

// AES加密函数
void aes_encrypt(unsigned char* message, unsigned char* key, int message_size, int key_size)
{
    // 通过密钥计算出轮密钥
    unsigned char round_key[176];
    key_expansion(key, round_key, key_size);

    // 将明文按照每个块128位进行分组，每个块内部进行AES加密
    for (int i = 0; i < message_size; i += 16)
    {
        unsigned char block[16];
        memcpy(block, message + i, 16);
        aes_encrypt_block(block, round_key);
        memcpy(message + i, block, 16);
    }
}

// AES加密块函数
void aes_encrypt_block(unsigned char* block, unsigned char* round_key)
{
    // 轮密钥加
    add_round_key(block, round_key, 0);

    // 9轮迭代
    for (int round = 1; round <= 9; round++)
    {
        sub_bytes(block);
        shift_rows(block);
        mix_columns(block);
        add_round_key(block, round_key, round * 16);
    }

    // 最后一轮
    sub_bytes(block);
    shift_rows(block);
    add_round_key(block, round_key, 160);
}

// 密钥扩展函数
void key_expansion(unsigned char* key, unsigned char* round_key, int key_size)
{
    // 初始轮密钥即为密钥
    memcpy(round_key, key, key_size);

    // 轮密钥扩展
    for (int i = key_size; i < 176; i += 4)
    {
        unsigned char temp[4];
        memcpy(temp, round_key + i - 4, 4);
        
        if (i % key_size == 0)
        {
            // 循环左移一位
            unsigned char t = temp[0];
            temp[0] = temp[1];
            temp[1] = temp[2];
            temp[2] = temp[3];
            temp[3] = t;

            // 字节代换
            temp[0] = s_box[temp[0]];
            temp[1] = s_box[temp[1]];
            temp[2] = s_box[temp[2]];
            temp[3] = s_box[temp[3]];

            // 异或上轮常数
            temp[0] ^= r_con[i / key_size];
        }
        else if (key_size > 24 && i % key_size == 16)
        {
            // 字节代换
            temp[0] = s_box[temp[0]];
            temp[1] = s_box[temp[1]];
            temp[2] = s_box[temp[2]];
            temp[3] = s_box[temp[3]];
        }

        // 异或上前4个字节
        temp[0] ^= round_key[i - key_size];
        temp[1] ^= round_key[i - key_size + 1];
        temp[2] ^= round_key[i - key_size + 2];
        temp[3] ^= round_key[i - key_size + 3];

        // 将扩展后的密钥放入轮密钥中
        memcpy(round_key + i, temp, 4);
    }
}

// 轮密钥加函数
void add_round_key(unsigned char* block, unsigned char* round_key, int offset)
{
    for (int i = 0; i < 16; i++)
    {
        block[i] ^= round_key[i + offset];
    }
}

// 字节代换函数
void sub_bytes(unsigned char* block)
{
    for (int i = 0; i < 16; i++)
    {
        block[i] = s_box[block[i]];
    }
}

// 行移位函数
void shift_rows(unsigned char* block)
{
    unsigned char temp[16];
    memcpy(temp, block, 16);

    // 第1行不变
    block[1] = temp[5];
    block[2] = temp[10];
    block[3] = temp[15];

    // 第2行循环左移1位
    block[5] = temp[9];
    block[6] = temp[14];
    block[7] = temp[3];
    block[9] = temp[13];
    block[10] = temp[2];
    block[11] = temp[7];

    // 第3行循环左移2位
    block[15] = temp[6];
    block[14] = temp[1];
    block[13] = temp[12];
    block[12] = temp[8];
    block[11] = temp[4];
    block[10] = temp[0];
}

// 列混淆函数
void mix_columns(unsigned char* block)
{
    for (int i = 0; i < 4; i++)
    {
        unsigned char a[4], b[4];
        memcpy(a, block + i * 4, 4);
        memcpy(b, block + i * 4, 4);

        // 列混淆矩阵
        block[i * 4] = gf_mul(0x02, a[0]) ^ gf_mul(0x03, a[1]) ^ gf_mul(0x01, a[2]) ^ gf_mul(0x01, a[3]);
        block[i * 4 + 1] = gf_mul(0x01, b[0]) ^ gf_mul(0x02, b[1]) ^ gf_mul(0x03, b[2]) ^ gf_mul(0x01, b[3]);
        block[i * 4 + 2] = gf_mul(0x01, a[0]) ^ gf_mul(0x01, a[1]) ^ gf_mul(0x02, a[2]) ^ gf_mul(0x03, a[3]);
        block[i * 4 + 3] = gf_mul(0x03, b[0]) ^ gf_mul(0x01, b[1]) ^ gf_mul(0x01, b[2]) ^ gf_mul(0x02, b[3]);
    }
}

// 有限域乘法函数
unsigned char gf_mul(unsigned char a, unsigned char b)
{
    unsigned char p = 0;
    for (int i = 0; i < 8; i++)
    {
        if (b & 1)
        {
            p ^= a;
        }
        bool hi_bit_set = a & 0x80;
        a <<= 1;
        if (hi_bit_set)
        {
            a ^= 0x1b;
        }
        b >>= 1;
    }
    return p;
}

// S盒
const unsigned char s_box[256] = {
    0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
    0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
    0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
    0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
    0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
    0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
    0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
    0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
    0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
    0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
    0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
    0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
    0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
    0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
    0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
    0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16
};

// 轮常数
const unsigned char r_con[10] = {
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
};

int main()
{
    // 明文和密钥
    unsigned char message[] = "hello world";
    unsigned char key[] = "secret key";

    // 加密
    aes_encrypt(message, key, strlen((char*)message), strlen((char*)key));

    // 输出密文
    std::cout << "Ciphertext: ";
    for (int i = 0; i < strlen((char*)message); i++)
    {
        printf("%02x ", message[i]);
    }
    std::cout << std::endl;

    return 0;
}