RC4加密算法，MCU中使用

 1 /******************** (C) COPYRIGHT 2012 WildFire Team **************************
10 **********************************************************************************/
11 #include "stm32f10x.h"
12 
13 void swap_byte(unsigned char *a, unsigned char *b);
14 /*rc4.c */
15 typedef struct rc4_key
16 {      
17      unsigned char state[256];       
18      unsigned char x;        
19      unsigned char y;
20 } rc4_key;
21 
22 void prepare_key(rc4_key *key, unsigned char *key_data_ptr, int key_data_len)
28 {
29   unsigned char index1;
31     unsigned char index2;
32     unsigned char *state;
33     short counter;     
34     state = &key->state[0];         
35     for(counter = 0; counter < 256; counter++)              
36     state[counter] = counter;               
37     key->x = 0;     
38     key->y = 0;     
39     index1 = 0;     
40     index2 = 0;             
41     for(counter = 0; counter < 256; counter++)      
42     {               
43         index2 = (key_data_ptr[index1] + state[counter] +index2) % 256;                
44         swap_byte(&state[counter], &state[index2]);            
45         index1 = (index1 + 1) % key_data_len;  
46     }       
47 }
48     
49 void rc4(rc4_key *key,unsigned char *buffer_ptr, int buffer_len )
50 { 
51     unsigned char x;
52     unsigned char y;
53     unsigned char* state;
54     unsigned char xorIndex;
55     short counter;                  
57     x = key->x;     
58     y = key->y;        
60     state = &key->state[0];         
61     for(counter = 0; counter < buffer_len; counter ++)      
62     {               
63          x = (x + 1) % 256;                      
64          y = (state[x] + y) % 256;               
65          swap_byte(&state[x], &state[y]);                        
66                   
67          xorIndex = (state[x] + state[y]) % 256;                 
68                   
69          buffer_ptr[counter] ^= state[xorIndex];         
70     }               
71     key->x = x;     
72     key->y = y;
73 }
74     
75 void swap_byte(unsigned char *a, unsigned char *b)
76 {
77     unsigned char swapByte; 
78        
79     swapByte = *a; 
80     *a = *b;      
81     *b = swapByte;
82 }
83 
84 unsigned char keys[9] = {8,0x01,0x23,0x45,0x67,0x89,0xab,0xcd,0xef};
85 
86 
87 int main()
88 {
89     rc4_key s;
90     unsigned char buffer[10] = {0,1,2,3,4,5,6,7,8,9};
91     //数据加密
92     prepare_key(&s, keys, 10);    //加密初始化
93     rc4(&s,buffer,10);            //将buffer加密，加密成功的数据放在s.state中
94     //数据解密
95        prepare_key(&s, keys, 10);    //解密初始化
96     rc4(&s,buffer,10);            //将s.state中的数据解密，解密后的数据放在buffer中
97 
98 }