C语言实现AES、DES加密算法：原理与代码示例

本文将介绍两种常用的对称加密算法：AES和DES，并提供C语言实现的代码示例。

1. AES加密算法

1.1 原理

AES（高级加密标准）是一种分组密码算法，它将明文数据分成128位（16字节）的块进行加密。AES算法使用密钥进行加密和解密，密钥长度可以是128位、192位或256位。

AES算法包含以下几个步骤：

字节替换（SubBytes）： 使用S盒将每个字节替换成另一个字节，进行非线性变换。
行移位（ShiftRows）： 对状态矩阵进行行移位操作，打乱字节顺序。
列混淆（MixColumns）： 对状态矩阵进行列混淆操作，进一步提高安全性。
轮密钥加（AddRoundKey）： 将轮密钥与状态矩阵进行异或运算，将密钥信息融入到数据中。

1.2 C语言实现

#include <stdio.h>
#include <stdint.h>

typedef uint8_t state_t[4][4];

static const uint8_t sbox[16][16] = {
  {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}
};

static const uint8_t rsbox[16][16] = {
  {0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb},
  {0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb},
  {0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e},
  {0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25},
  {0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92},
  {0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84},
  {0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06},
  {0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b},
  {0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73},
  {0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e},
  {0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b},
  {0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4},
  {0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f},
  {0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef},
  {0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61},
  {0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d}
};

static const uint8_t Rcon[11] = {
  0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
};

// 字节替换
void SubBytes(state_t* state) {
  int i, j;
  for (i = 0; i < 4; i++) {
    for (j = 0; j < 4; j++) {
      (*state)[i][j] = sbox[((*state)[i][j] & 0xf0) >> 4][(*state)[i][j] & 0x0f];
    }
  }
}

// 行移位
void ShiftRows(state_t* state) {
  uint8_t tmp;

  // row 1
  tmp = (*state)[1][0];
  (*state)[1][0] = (*state)[1][1];
  (*state)[1][1] = (*state)[1][2];
  (*state)[1][2] = (*state)[1][3];
  (*state)[1][3] = tmp;

  // row 2
  tmp = (*state)[2][0];
  (*state)[2][0] = (*state)[2][2];
  (*state)[2][2] = tmp;
  tmp = (*state)[2][1];
  (*state)[2][1] = (*state)[2][3];
  (*state)[2][3] = tmp;

  // row 3
  tmp = (*state)[3][3];
  (*state)[3][3] = (*state)[3][2];
  (*state)[3][2] = (*state)[3][1];
  (*state)[3][1] = (*state)[3][0];
  (*state)[3][0] = tmp;
}

// 列混淆
void MixColumns(state_t* state) {
  int i;
  uint8_t Tmp, Tm, t;
  for (i = 0; i < 4; i++) {
    t = (*state)[i][0];
    Tmp = (*state)[i][0] ^ (*state)[i][1] ^ (*state)[i][2] ^ (*state)[i][3];
    Tm = (*state)[i][0] ^ (*state)[i][1];
    Tm = xtime(Tm);
    (*state)[i][0] ^= Tm ^ Tmp;
    Tm = (*state)[i][1] ^ (*state)[i][2];
    Tm = xtime(Tm);
    (*state)[i][1] ^= Tm ^ Tmp;
    Tm = (*state)[i][2] ^ (*state)[i][3];
    Tm = xtime(Tm);
    (*state)[i][2] ^= Tm ^ Tmp;
    Tm = (*state)[i][3] ^ t;
    Tm = xtime(Tm);
    (*state)[i][3] ^= Tm ^ Tmp;
  }
}

// 轮密钥加
void AddRoundKey(state_t* state, const uint8_t* roundKey) {
  int i, j;
  for (i = 0; i < 4; i++) {
    for (j = 0; j < 4; j++) {
      (*state)[j][i] ^= roundKey[i * 4 + j];
    }
  }
}

// 密钥扩展
void KeyExpansion(const uint8_t* key, uint8_t* roundKey) {
  int i, j, k;
  uint8_t tempa[4];

  for (i = 0; i < 4; i++) {
    roundKey[(i * 4) + 0] = key[(i * 4) + 0];
    roundKey[(i * 4) + 1] = key[(i * 4) + 1];
    roundKey[(i * 4) + 2] = key[(i * 4) + 2];
    roundKey[(i * 4) + 3] = key[(i * 4) + 3];
  }

  for (i = 4; i < 44; ++i) {
    for (j = 0; j < 4; ++j) {
      tempa[j] = roundKey[(i - 1) * 4 + j];
    }
    if (i % 4 == 0) {
      uint8_t temp = tempa[0];
      tempa[0] = tempa[1];
      tempa[1] = tempa[2];
      tempa[2] = tempa[3];
      tempa[3] = temp;
      for (j = 0; j < 4; ++j) {
        tempa[j] = sbox[tempa[j] & 0x0f][tempa[j] >> 4];
      }
      tempa[0] ^= Rcon[i / 4];
    }
    for (j = 0; j < 4; ++j) {
      roundKey[i * 4 + j] = roundKey[(i - 4) * 4 + j] ^ tempa[j];
    }
  }
}

// AES加密
void AES_Encrypt(const uint8_t* message, const uint8_t* key, uint8_t* ciphertext) {
  int i, j, round = 0;
  state_t state;
  uint8_t roundKey[240];

  KeyExpansion(key, roundKey);

  for (i = 0; i < 4; ++i) {
    for (j = 0; j < 4; ++j) {
      state[j][i] = message[i * 4 + j];
    }
  }

  AddRoundKey(&state, roundKey);

  for (round = 1; round < 10; ++round) {
    SubBytes(&state);
    ShiftRows(&state);
    MixColumns(&state);
    AddRoundKey(&state, roundKey + (round * 4 * 4));
  }

  SubBytes(&state);
  ShiftRows(&state);
  AddRoundKey(&state, roundKey + (round * 4 * 4));

  for (i = 0; i < 4; ++i) {
    for (j = 0; j < 4; ++j) {
      ciphertext[i * 4 + j] = state[j][i];
    }
  }
}

// AES解密
void AES_Decrypt(const uint8_t* ciphertext, const uint8_t* key, uint8_t* message) {
  int i, j, round = 0;
  state_t state;
  uint8_t roundKey[240];

  KeyExpansion(key, roundKey);

  for (i = 0; i < 4; ++i) {
    for (j = 0; j < 4; ++j) {
      state[j][i] = ciphertext[i * 4 + j];
    }
  }

  AddRoundKey(&state, roundKey + (10 * 4 * 4));

  for (round = 9; round > 0; --round) {
    InvShiftRows(&state);
    InvSubBytes(&state);
    AddRoundKey(&state, roundKey + (round * 4 * 4));
    InvMixColumns(&state);
  }

  InvShiftRows(&state);
  InvSubBytes(&state);
  AddRoundKey(&state, roundKey);

  for (i = 0; i < 4; ++i) {
    for (j = 0; j < 4; ++j) {
      message[i * 4 + j] = state[j][i];
    }
  }
}

// ... (其他辅助函数：xtime, InvShiftRows, InvSubBytes, InvMixColumns)

int main() {
  // 密钥
  uint8_t key[16] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};

  // 明文
  uint8_t message[16] = {'T', 'h', 'i', 's', ' ', 'i', 's', ' ', 'a', ' ', 't', 'e', 's', 't', ' ', '!'};

  // 密文
  uint8_t ciphertext[16];

  // 加密
  AES_Encrypt(message, key, ciphertext);

  // 解密
  uint8_t decrypted[16];
  AES_Decrypt(ciphertext, key, decrypted);

  // 打印结果
  printf("密文: ");
  for (int i = 0; i < 16; i++) {
    printf("%02x ", ciphertext[i]);
  }
  printf("\n");
  printf("解密后明文: ");
  for (int i = 0; i < 16; i++) {
    printf("%c", decrypted[i]);
  }
  printf("\n");

  return 0;
}

2. DES加密算法

2.1 原理

DES（数据加密标准）是一种分组密码算法，它将明文数据分成64位（8字节）的块进行加密。DES算法使用56位的密钥进行加密和解密。

DES算法包含以下几个步骤：

初始置换（IP）： 对64位明文进行初始置换。
16轮Feistel函数： 循环进行16轮Feistel函数运算，每轮使用不同的子密钥。
逆初始置换（IP-1）： 对最终结果进行逆初始置换，得到密文。

2.2 C语言实现

#include <stdio.h>
#include <stdint.h>

// DES密钥
typedef struct {
  uint64_t key; // 64位密钥
} DES_Key;

// DES算法常量
static const uint64_t IP[8] = {0x40100400, 0x80200800, 0x10401000, 0x20802000, 0x04000401, 0x08000802, 0x10001004, 0x20002008};
static const uint64_t IP_1[8] = {0x00000001, 0x00000002, 0x00000004, 0x00000008, 0x00000010, 0x00000020, 0x00000040, 0x00000080};
static const uint64_t PC1[8] = {0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x56000000, 0xa0000000, 0x08000000, 0x00000000};
static const uint64_t PC2[8] = {0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x52000000, 0xa2000000, 0x02000000, 0x00000000};

// 生成子密钥
void DES_KeyExpansion(DES_Key* key, uint64_t* subKeys) {
  // ... (密钥扩展过程)
}

// Feistel函数
uint64_t DES_Feistel(uint64_t left, uint64_t right, uint64_t subKey) {
  // ... (Feistel函数实现)
}

// DES加密
void DES_Encrypt(uint64_t message, DES_Key* key, uint64_t* ciphertext) {
  // ... (DES加密实现)
}

// DES解密
void DES_Decrypt(uint64_t ciphertext, DES_Key* key, uint64_t* message) {
  // ... (DES解密实现)
}

// ... (其他辅助函数)

int main() {
  // 密钥
  DES_Key key;
  key.key = 0x0123456789ABCDEF; // 示例密钥

  // 明文
  uint64_t message = 0x123456789ABCDEF0; // 示例明文

  // 密文
  uint64_t ciphertext;

  // 加密
  DES_Encrypt(message, &key, &ciphertext);

  // 解密
  uint64_t decrypted;
  DES_Decrypt(ciphertext, &key, &decrypted);

  // 打印结果
  printf("密文: %llx\n", ciphertext);
  printf("解密后明文: %llx\n", decrypted);

  return 0;
}

注意： 由于DES算法的密钥长度较短，安全性较低，建议使用AES算法进行加密。

总结

本文介绍了AES和DES两种常见加密算法的原理和C语言实现方法。通过本文的学习，您能够更加深入地理解加密算法的实现机制，并能够自己动手编写简单的加密解密程序。

建议： 在实际应用中，建议使用安全可靠的加密库，例如OpenSSL，来进行加密和解密操作，以确保数据安全。