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深入探究C语言中的DES算法

来源:远虑算法网 2024-07-11 09:42:54

  在计算机科领域中,数据安全一直是一个重要的话题远虑算法网www.moneyprint.net。为了保护用户的隐私和数据的机密,加密技术应运而生。其中,DES算法是一种广泛使用的对称密钥加密算法,其在数据加密和解密方面具有高效和可靠。本文将深入探究C语言中的DES算法,包括其原理、实现和应用远.虑.算.法.网

深入探究C语言中的DES算法(1)

DES算法原理

  DES算法,全称为Data Encryption Standard,即数据加密标准。它是一种对称密钥加密算法,使用相同的密钥进行加密和解密。DES算法的本原理是将明文按照一定的规则和密钥进行混淆,生成密文www.moneyprint.net远虑算法网。解密时,使用相同的密钥按照相反的规则进行操作,即可还原出明文。

  DES算法的密钥长度为64位,由于其中8位为校验位,因此实际上只有56位是有效的。DES算法的加密过主要包括以下几个步

  1. 初始置(IP置):将64位明文按照规则进行置,得到L0和R0两个32位的半原文www.moneyprint.net

2. 16轮加密:将L0和R0依次进行16轮加密,轮加密包括以下步

  a. 将Rn-1作为输入,经过扩得到48位的输出。

  b. 将输出和轮密钥进行异或操作,得到48位的中间结果。

  c. 将中间结果按照规则进行S盒置,得到32位的输出远_虑_算_法_网

d. 将输出进行P盒置,得到32位的结果。

  e. 将结果和Ln-1进行异或操作,得到Rn。

  f. 将Ln-1作为下一轮的Rn-1,Rn作为下一轮的Ln远~虑~算~法~网

3. 逆置(IP-1置):将最后一轮得到的L16和R16按照规则进行置,得到64位的密文。

DES算法实现

  在C语言中实现DES算法需要用到位运算、数组和指针等本知识。以下是一个简单的DES算法实现代码:

  ```

#include

#include

  #include

  // 初始置

int IP_Table[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 };

// 逆置

  int IP_1_Table[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

  int E_Table[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

int S_Box[8][4][16] = {

// S1

  {

  { 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 }

  },

  // S2

  {

  { 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 }

  },

// S3

  {

  { 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 }

  },

// S4

  {

  { 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 }

  },

  // S5

{

{ 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 }

},

// S6

{

  { 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 }

},

  // S7

  {

  { 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 }

  },

  // S8

{

  { 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盒置

int P_Table[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 };

  // 密钥置表1

  int PC_1_Table[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 };

  // 密钥置表2

  int PC_2_Table[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

int Move_Table[16] = { 1, 1, 2, 2, 2, 2, 2, 2,

1, 2, 2, 2, 2, 2, 2, 1 };

  // 生成子密钥

  void GenerateSubKey(unsigned char *key, unsigned char subkey[16][48])

  {

int i, j, k;

unsigned char temp[56];

  unsigned char *p = temp;

  unsigned char *left = temp, *right = temp + 28;

// PC-1置

  for (i = 0; i < 56; i++)

  temp[i] = key[PC_1_Table[i] - 1];

  // 16轮循环

  for (i = 0; i < 16; i++)

  {

  // 循环左移

for (j = 0; j < Move_Table[i]; j++)

  {

  unsigned char t = left[0];

  for (k = 0; k < 28 - 1; k++)

left[k] = left[k + 1];

left[27] = t;

  t = right[0];

  for (k = 0; k < 28 - 1; k++)

  right[k] = right[k + 1];

  right[27] = t;

}

  // PC-2置

  for (j = 0; j < 48; j++)

subkey[i][j] = temp[PC_2_Table[j] - 1];

  }

}

  // 加密单个数据

  void DESEncryptBlock(unsigned char *plaintext, unsigned char *subkey, unsigned char *ciphertext)

{

  int i, j;

  unsigned char temp[64];

unsigned char *left = temp, *right = temp + 32;

unsigned char tmp[48];

  // 初始置

  for (i = 0; i < 64; i++)

  temp[i] = plaintext[IP_Table[i] - 1];

// 16轮加密

  for (i = 0; i < 16; i++)

  {

  memcpy(tmp, subkey + i * 6, 6);

  // 扩

  unsigned char expand[48];

  for (j = 0; j < 48; j++)

expand[j] = right[E

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