RC4加解密源码

本文介绍RC4加解密源码。

RC4（来自Rivest Cipher 4的缩写）是一种流加密算法，密钥长度可变。它加解密使用相同的密钥，因此也属于对称加密算法。RC4具有加解密速度快，算法简单等优点，在算力不高场合（MCU）也可以使用。

1.源码

1)头文件

头文件（rc4.h）主要包括RC4相关数据结构定义及外部函数声明。头文件定义如下。

#ifndef __RC4_H
#define __RC4_H


#ifdef __cplusplus
 extern "C" {
#endif 


typedef struct _RC4_INFO
{
    uint8_t s[256];
    uint8_t t[256];
}RC4_INFO;     

 
extern void rc4_init(RC4_INFO *RC4Info, const uint8_t *key, uint32_t len);
extern void rc4_crypt(RC4_INFO *RC4Info, const uint8_t *input, uint8_t *output, uint32_t len);    
     

#ifdef __cplusplus
}
#endif



#endif

注意：

a)加密过程，需要先调用rc4_init()函数，再调用rc4_crypt()函数，同样，解密过程，也需要先调用rc4_init()函数，再调用rc4_crypt()函数。加解密使用的是同一个密钥。

b)密钥长度可变，一般为8-256 bits，常用128 bits。

2)源文件

源文件（rc4. c）主要包括RC4相关外部函数定义。源文件定义如下。

#include "rc4.h"


static void swap(uint8_t *p1, uint8_t *p2);


void rc4_init(RC4_INFO *RC4Info, const uint8_t *key, uint32_t len)
{
    uint32_t i = 0;
    uint32_t j = 0;

    if ((RC4Info == NULL) || (key == NULL) || (len == 0))
    {
        return ;
    }

    //Initial values of both vectors
    for (i = 0; i < 256; i++)
    {
        RC4Info->s[i] = (uint8_t)i;
        RC4Info->t[i] = key[i % len];
    }

    //Initial permutation
    for (i = 0; i < 256; i++)
    {
        j = (j + RC4Info->s[i] + RC4Info->t[i]) % 256;
        swap(&RC4Info->s[i], &RC4Info->s[j]);
    }
}


void rc4_crypt(RC4_INFO *RC4Info, const uint8_t *input, uint8_t *output, uint32_t len)
{
    uint32_t i = 0;
    uint8_t t1 = 0;
    uint8_t t2 = 0;
    uint8_t val = 0;
    uint8_t out = 0;

    if ((RC4Info == NULL) || (input == NULL) || (output == NULL) || (len == 0))
    {
        return ;
    }

    //process one byte at a time
    for (i = 0; i < len; i++)
    {
        t1 = (t1 + 1) % 256;
        t2 = (t2 + RC4Info->s[t1]) % 256;
        swap(&RC4Info->s[t1], &RC4Info->s[t2]);
        val = (RC4Info->s[t1] + RC4Info->s[t2]) % 256;
        out = *input++ ^ RC4Info->s[val];
        *output++ = out;
    }
}


static void swap(uint8_t *p1, uint8_t *p2)
{
    uint8_t t = 0;

    if ((p1 == NULL) || (p2 == NULL))
    {
        return ;
    }

    t = *p1;
    *p1 = *p2;
    *p2 = t;
}

2.测试

这里主要测试加解密过程。

int main()
{
    RC4_INFO RC4Info;
    uint8_t key[] = {0x03, 0x01, 0x02, 0x03, 0x04, 0x08, 0x09, 0x1a};
    uint8_t data[] = {0x03, 0x04, 0x08, 0x09, 0xa5, 0x5a, 0x33, 0x22, 0x88};
    uint8_t encrypt[256] = {0};
    uint8_t decrypt[256] = {0};
    uint32_t i = 0;

    printf("raw data:\r\n");
    for (i = 0; i < sizeof(data) / sizeof(data[0]); i++)
    {
        printf("0x%02x ", data[i]);
    }
    printf("\r\n");

    //encrypt
    rc4_init(&RC4Info, key, sizeof(key) / sizeof(key[0]));
    rc4_crypt(&RC4Info, data, encrypt,  sizeof(data) / sizeof(data[0]));

    printf("encrypted data:\r\n");
    for (i = 0; i < sizeof(data) / sizeof(data[0]); i++)
    {
        printf("0x%02x ", encrypt[i]);
    }
    printf("\r\n");

    //decrypt
    rc4_init(&RC4Info, key, sizeof(key) / sizeof(key[0]));
    rc4_crypt(&RC4Info, encrypt, decrypt,  sizeof(data) / sizeof(data[0]));

    printf("decrypted data:\r\n");
    for (i = 0; i <  sizeof(data) / sizeof(data[0]); i++)
    {
        printf("0x%02x ", decrypt[i]);
    }
    printf("\r\n");

    return 0;
}

输出结果：

总结，本文介绍了RC4加解密源码。