RC4加密算法，MCU中使用

/******************** (C) COPYRIGHT 2012 WildFire Team **************************
**********************************************************************************/
#include "stm32f10x.h"

void swap_byte(unsigned char *a, unsigned char *b);
/*rc4.c */
typedef struct rc4_key
{      
     unsigned char state[256];       
     unsigned char x;        
     unsigned char y;
} rc4_key;

void prepare_key(rc4_key *key, unsigned char *key_data_ptr, int key_data_len)
{
  unsigned char index1;
    unsigned char index2;
    unsigned char *state;
    short counter;     
    state = &key->state[0];         
    for(counter = 0; counter < 256; counter++)              
    state[counter] = counter;               
    key->x = 0;     
    key->y = 0;     
    index1 = 0;     
    index2 = 0;             
    for(counter = 0; counter < 256; counter++)      
    {               
        index2 = (key_data_ptr[index1] + state[counter] +index2) % 256;                
        swap_byte(&state[counter], &state[index2]);            
        index1 = (index1 + 1) % key_data_len;  
    }       
}
    
void rc4(rc4_key *key,unsigned char *buffer_ptr, int buffer_len )
{ 
    unsigned char x;
    unsigned char y;
    unsigned char* state;
    unsigned char xorIndex;
    short counter;                  
    x = key->x;     
    y = key->y;        
    state = &key->state[0];         
    for(counter = 0; counter < buffer_len; counter ++)      
    {               
         x = (x + 1) % 256;                      
         y = (state[x] + y) % 256;               
         swap_byte(&state[x], &state[y]);                        
                  
         xorIndex = (state[x] + state[y]) % 256;                 
                  
         buffer_ptr[counter] ^= state[xorIndex];         
    }               
    key->x = x;     
    key->y = y;
}
    
void swap_byte(unsigned char *a, unsigned char *b)
{
    unsigned char swapByte; 
       
    swapByte = *a; 
    *a = *b;      
    *b = swapByte;
}

unsigned char keys[9] = {8,0x01,0x23,0x45,0x67,0x89,0xab,0xcd,0xef};


int main()
{
    rc4_key s;
    unsigned char buffer[10] = {0,1,2,3,4,5,6,7,8,9};
    //数据加密
    prepare_key(&s, keys, 10);    //加密初始化
    rc4(&s,buffer,10);            //将buffer加密，加密成功的数据放在s.state中
    //数据解密
       prepare_key(&s, keys, 10);    //解密初始化
    rc4(&s,buffer,10);            //将s.state中的数据解密，解密后的数据放在buffer中

}